1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Error Handling</title> 5<link rel="stylesheet" href="../math.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Math Toolkit 2.12.0"> 8<link rel="up" href="../overview.html" title="Chapter 1. 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For example if <a class="link" href="sf_gamma/tgamma.html" title="Gamma">tgamma</a> 70 is evaluated at exactly -2, the function approaches different limiting 71 values depending upon whether you approach from just above or just below 72 -2. Hence the function has no well defined value at this point and a 73 Pole Error will be raised. 74 </p></dd> 75<dt><span class="term">Overflow Error</span></dt> 76<dd><p> 77 Occurs when the result is either infinite, or too large to represent 78 in the numeric type being returned by the function. 79 </p></dd> 80<dt><span class="term">Underflow Error</span></dt> 81<dd><p> 82 Occurs when the result is not zero, but is too small to be represented 83 by any other value in the type being returned by the function. 84 </p></dd> 85<dt><span class="term">Denormalisation Error</span></dt> 86<dd><p> 87 Occurs when the returned result would be a denormalised value. 88 </p></dd> 89<dt><span class="term">Rounding Error</span></dt> 90<dd><p> 91 Occurs when the argument to one of the rounding functions <a class="link" href="rounding/trunc.html" title="Truncation Functions">trunc</a>, 92 <a class="link" href="rounding/round.html" title="Rounding Functions">round</a> and <a class="link" href="rounding/modf.html" title="Integer and Fractional Part Splitting (modf)">modf</a> 93 can not be represented as an integer type, is outside the range of the 94 result type. 95 </p></dd> 96<dt><span class="term">Evaluation Error</span></dt> 97<dd><p> 98 Occurs if no method of evaluation is known, or when an internal error 99 occurred that prevented the result from being evaluated: this should 100 never occur, but if it does, then it's likely to be due to an iterative 101 method not converging fast enough. 102 </p></dd> 103<dt><span class="term">Indeterminate Result Error</span></dt> 104<dd><p> 105 Occurs when the result of a function is not defined for the values that 106 were passed to it. 107 </p></dd> 108</dl> 109</div> 110<p> 111 The action undertaken by each error condition is determined by the current 112 <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> in effect. This can be changed program-wide 113 by setting some configuration macros, or at namespace scope, or at the call 114 site (by specifying a specific policy in the function call). 115 </p> 116<p> 117 The available actions are: 118 </p> 119<div class="variablelist"> 120<p class="title"><b></b></p> 121<dl class="variablelist"> 122<dt><span class="term">throw_on_error</span></dt> 123<dd><p> 124 Throws the exception most appropriate to the error condition. 125 </p></dd> 126<dt><span class="term">errno_on_error</span></dt> 127<dd><p> 128 Sets ::errno to an appropriate value, and then returns the most appropriate 129 result 130 </p></dd> 131<dt><span class="term">ignore_error</span></dt> 132<dd><p> 133 Ignores the error and simply the returns the most appropriate result. 134 </p></dd> 135<dt><span class="term">user_error</span></dt> 136<dd><p> 137 Calls a <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">user-supplied 138 error handler</a>. 139 </p></dd> 140</dl> 141</div> 142<p> 143 The following tables show all the permutations of errors and actions, with 144 the <span class="bold"><strong>default action for each error shown in bold</strong></span>: 145 </p> 146<div class="table"> 147<a name="math_toolkit.error_handling.possible_actions_for_domain_erro"></a><p class="title"><b>Table 1.1. Possible Actions for Domain Errors</b></p> 148<div class="table-contents"><table class="table" summary="Possible Actions for Domain Errors"> 149<colgroup> 150<col> 151<col> 152</colgroup> 153<thead><tr> 154<th> 155 <p> 156 Action 157 </p> 158 </th> 159<th> 160 <p> 161 Behaviour 162 </p> 163 </th> 164</tr></thead> 165<tbody> 166<tr> 167<td> 168 <p> 169 throw_on_error 170 </p> 171 </td> 172<td> 173 <p> 174 <span class="bold"><strong>Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">domain_error</span></code></strong></span> 175 </p> 176 </td> 177</tr> 178<tr> 179<td> 180 <p> 181 errno_on_error 182 </p> 183 </td> 184<td> 185 <p> 186 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 187 to <code class="computeroutput"><span class="identifier">EDOM</span></code> and returns 188 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">()</span></code> 189 </p> 190 </td> 191</tr> 192<tr> 193<td> 194 <p> 195 ignore_error 196 </p> 197 </td> 198<td> 199 <p> 200 Returns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">()</span></code> 201 </p> 202 </td> 203</tr> 204<tr> 205<td> 206 <p> 207 user_error 208 </p> 209 </td> 210<td> 211 <p> 212 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_domain_error</span></code>: 213 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 214 must be defined by the user</a>. 215 </p> 216 </td> 217</tr> 218</tbody> 219</table></div> 220</div> 221<br class="table-break"><div class="table"> 222<a name="math_toolkit.error_handling.possible_actions_for_pole_errors"></a><p class="title"><b>Table 1.2. Possible Actions for Pole Errors</b></p> 223<div class="table-contents"><table class="table" summary="Possible Actions for Pole Errors"> 224<colgroup> 225<col> 226<col> 227</colgroup> 228<thead><tr> 229<th> 230 <p> 231 Action 232 </p> 233 </th> 234<th> 235 <p> 236 Behaviour 237 </p> 238 </th> 239</tr></thead> 240<tbody> 241<tr> 242<td> 243 <p> 244 throw_on_error 245 </p> 246 </td> 247<td> 248 <p> 249 <span class="bold"><strong>Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">domain_error</span></code></strong></span> 250 </p> 251 </td> 252</tr> 253<tr> 254<td> 255 <p> 256 errno_on_error 257 </p> 258 </td> 259<td> 260 <p> 261 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 262 to <code class="computeroutput"><span class="identifier">EDOM</span></code> and returns 263 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">()</span></code> 264 </p> 265 </td> 266</tr> 267<tr> 268<td> 269 <p> 270 ignore_error 271 </p> 272 </td> 273<td> 274 <p> 275 Returns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">()</span></code> 276 </p> 277 </td> 278</tr> 279<tr> 280<td> 281 <p> 282 user_error 283 </p> 284 </td> 285<td> 286 <p> 287 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_pole_error</span></code>: 288 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 289 must be defined by the user</a>. 290 </p> 291 </td> 292</tr> 293</tbody> 294</table></div> 295</div> 296<br class="table-break"><div class="table"> 297<a name="math_toolkit.error_handling.possible_actions_for_overflow_er"></a><p class="title"><b>Table 1.3. Possible Actions for Overflow Errors</b></p> 298<div class="table-contents"><table class="table" summary="Possible Actions for Overflow Errors"> 299<colgroup> 300<col> 301<col> 302</colgroup> 303<thead><tr> 304<th> 305 <p> 306 Action 307 </p> 308 </th> 309<th> 310 <p> 311 Behaviour 312 </p> 313 </th> 314</tr></thead> 315<tbody> 316<tr> 317<td> 318 <p> 319 throw_on_error 320 </p> 321 </td> 322<td> 323 <p> 324 <span class="bold"><strong>Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">overflow_error</span></code></strong></span> 325 </p> 326 </td> 327</tr> 328<tr> 329<td> 330 <p> 331 errno_on_error 332 </p> 333 </td> 334<td> 335 <p> 336 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 337 to <code class="computeroutput"><span class="identifier">ERANGE</span></code> and returns 338 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">infinity</span><span class="special">()</span></code> 339 </p> 340 </td> 341</tr> 342<tr> 343<td> 344 <p> 345 ignore_error 346 </p> 347 </td> 348<td> 349 <p> 350 Returns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">infinity</span><span class="special">()</span></code> 351 </p> 352 </td> 353</tr> 354<tr> 355<td> 356 <p> 357 user_error 358 </p> 359 </td> 360<td> 361 <p> 362 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_overflow_error</span></code>: 363 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 364 must be defined by the user</a>. 365 </p> 366 </td> 367</tr> 368</tbody> 369</table></div> 370</div> 371<br class="table-break"><div class="table"> 372<a name="math_toolkit.error_handling.possible_actions_for_underflow_e"></a><p class="title"><b>Table 1.4. Possible Actions for Underflow Errors</b></p> 373<div class="table-contents"><table class="table" summary="Possible Actions for Underflow Errors"> 374<colgroup> 375<col> 376<col> 377</colgroup> 378<thead><tr> 379<th> 380 <p> 381 Action 382 </p> 383 </th> 384<th> 385 <p> 386 Behaviour 387 </p> 388 </th> 389</tr></thead> 390<tbody> 391<tr> 392<td> 393 <p> 394 throw_on_error 395 </p> 396 </td> 397<td> 398 <p> 399 Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underflow_error</span></code> 400 </p> 401 </td> 402</tr> 403<tr> 404<td> 405 <p> 406 errno_on_error 407 </p> 408 </td> 409<td> 410 <p> 411 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 412 to <code class="computeroutput"><span class="identifier">ERANGE</span></code> and returns 413 0. 414 </p> 415 </td> 416</tr> 417<tr> 418<td> 419 <p> 420 ignore_error 421 </p> 422 </td> 423<td> 424 <p> 425 <span class="bold"><strong>Returns 0</strong></span> 426 </p> 427 </td> 428</tr> 429<tr> 430<td> 431 <p> 432 user_error 433 </p> 434 </td> 435<td> 436 <p> 437 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_underflow_error</span></code>: 438 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 439 must be defined by the user</a>. 440 </p> 441 </td> 442</tr> 443</tbody> 444</table></div> 445</div> 446<br class="table-break"><div class="table"> 447<a name="math_toolkit.error_handling.possible_actions_for_denorm_erro"></a><p class="title"><b>Table 1.5. Possible Actions for Denorm Errors</b></p> 448<div class="table-contents"><table class="table" summary="Possible Actions for Denorm Errors"> 449<colgroup> 450<col> 451<col> 452</colgroup> 453<thead><tr> 454<th> 455 <p> 456 Action 457 </p> 458 </th> 459<th> 460 <p> 461 Behaviour 462 </p> 463 </th> 464</tr></thead> 465<tbody> 466<tr> 467<td> 468 <p> 469 throw_on_error 470 </p> 471 </td> 472<td> 473 <p> 474 Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underflow_error</span></code> 475 </p> 476 </td> 477</tr> 478<tr> 479<td> 480 <p> 481 errno_on_error 482 </p> 483 </td> 484<td> 485 <p> 486 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 487 to <code class="computeroutput"><span class="identifier">ERANGE</span></code> and returns 488 the denormalised value. 489 </p> 490 </td> 491</tr> 492<tr> 493<td> 494 <p> 495 ignore_error 496 </p> 497 </td> 498<td> 499 <p> 500 <span class="bold"><strong>Returns the denormalised value.</strong></span> 501 </p> 502 </td> 503</tr> 504<tr> 505<td> 506 <p> 507 user_error 508 </p> 509 </td> 510<td> 511 <p> 512 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_denorm_error</span></code>: 513 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 514 must be defined by the user</a>. 515 </p> 516 </td> 517</tr> 518</tbody> 519</table></div> 520</div> 521<br class="table-break"><div class="table"> 522<a name="math_toolkit.error_handling.possible_actions_for_rounding_er"></a><p class="title"><b>Table 1.6. Possible Actions for Rounding Errors</b></p> 523<div class="table-contents"><table class="table" summary="Possible Actions for Rounding Errors"> 524<colgroup> 525<col> 526<col> 527</colgroup> 528<thead><tr> 529<th> 530 <p> 531 Action 532 </p> 533 </th> 534<th> 535 <p> 536 Behaviour 537 </p> 538 </th> 539</tr></thead> 540<tbody> 541<tr> 542<td> 543 <p> 544 throw_on_error 545 </p> 546 </td> 547<td> 548 <p> 549 Throws <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">rounding_error</span></code> 550 </p> 551 </td> 552</tr> 553<tr> 554<td> 555 <p> 556 errno_on_error 557 </p> 558 </td> 559<td> 560 <p> 561 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 562 to <code class="computeroutput"><span class="identifier">ERANGE</span></code> and returns 563 the largest representable value of the target integer type (or the 564 most negative value if the argument to the function was less than 565 zero). 566 </p> 567 </td> 568</tr> 569<tr> 570<td> 571 <p> 572 ignore_error 573 </p> 574 </td> 575<td> 576 <p> 577 <span class="bold"><strong>Returns the largest representable value of 578 the target integer type (or the most negative value if the argument 579 to the function was less than zero).</strong></span> 580 </p> 581 </td> 582</tr> 583<tr> 584<td> 585 <p> 586 user_error 587 </p> 588 </td> 589<td> 590 <p> 591 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_rounding_error</span></code>: 592 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 593 must be defined by the user</a>. 594 </p> 595 </td> 596</tr> 597</tbody> 598</table></div> 599</div> 600<br class="table-break"><div class="table"> 601<a name="math_toolkit.error_handling.possible_actions_for_internal_ev"></a><p class="title"><b>Table 1.7. Possible Actions for Internal Evaluation Errors</b></p> 602<div class="table-contents"><table class="table" summary="Possible Actions for Internal Evaluation Errors"> 603<colgroup> 604<col> 605<col> 606</colgroup> 607<thead><tr> 608<th> 609 <p> 610 Action 611 </p> 612 </th> 613<th> 614 <p> 615 Behaviour 616 </p> 617 </th> 618</tr></thead> 619<tbody> 620<tr> 621<td> 622 <p> 623 throw_on_error 624 </p> 625 </td> 626<td> 627 <p> 628 <span class="bold"><strong>Throws <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">evaluation_error</span></code></strong></span> 629 </p> 630 </td> 631</tr> 632<tr> 633<td> 634 <p> 635 errno_on_error 636 </p> 637 </td> 638<td> 639 <p> 640 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 641 to <code class="computeroutput"><span class="identifier">EDOM</span></code> and returns 642 the closest approximation found. 643 </p> 644 </td> 645</tr> 646<tr> 647<td> 648 <p> 649 ignore_error 650 </p> 651 </td> 652<td> 653 <p> 654 Returns the closest approximation found. 655 </p> 656 </td> 657</tr> 658<tr> 659<td> 660 <p> 661 user_error 662 </p> 663 </td> 664<td> 665 <p> 666 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_evaluation_error</span></code>: 667 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 668 must be defined by the user</a>. 669 </p> 670 </td> 671</tr> 672</tbody> 673</table></div> 674</div> 675<br class="table-break"><div class="table"> 676<a name="math_toolkit.error_handling.possible_actions_for_indetermina"></a><p class="title"><b>Table 1.8. Possible Actions for Indeterminate Result Errors</b></p> 677<div class="table-contents"><table class="table" summary="Possible Actions for Indeterminate Result Errors"> 678<colgroup> 679<col> 680<col> 681</colgroup> 682<thead><tr> 683<th> 684 <p> 685 Action 686 </p> 687 </th> 688<th> 689 <p> 690 Behaviour 691 </p> 692 </th> 693</tr></thead> 694<tbody> 695<tr> 696<td> 697 <p> 698 throw_on_error 699 </p> 700 </td> 701<td> 702 <p> 703 Throws <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">domain_error</span></code> 704 </p> 705 </td> 706</tr> 707<tr> 708<td> 709 <p> 710 errno_on_error 711 </p> 712 </td> 713<td> 714 <p> 715 Sets <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> 716 to <code class="computeroutput"><span class="identifier">EDOM</span></code> and returns 717 the same value as <code class="computeroutput"><span class="identifier">ignore_error</span></code>. 718 </p> 719 </td> 720</tr> 721<tr> 722<td> 723 <p> 724 ignore_error 725 </p> 726 </td> 727<td> 728 <p> 729 <span class="bold"><strong>Returns a default result that depends on the 730 function where the error occurred.</strong></span> 731 </p> 732 </td> 733</tr> 734<tr> 735<td> 736 <p> 737 user_error 738 </p> 739 </td> 740<td> 741 <p> 742 Returns the result of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">user_indeterminate_result_error</span></code>: 743 <a class="link" href="pol_tutorial/user_def_err_pol.html" title="Calling User Defined Error Handlers">this function 744 must be defined by the user</a>. 745 </p> 746 </td> 747</tr> 748</tbody> 749</table></div> 750</div> 751<br class="table-break"><p> 752 All these error conditions are in namespace boost::math::policies, made available, 753 for example, a by namespace declaration using <code class="computeroutput"><span class="keyword">namespace</span> 754 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">;</span></code> or individual using declarations <code class="computeroutput"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">overflow_error</span><span class="special">;</span></code>. 755 </p> 756<h4> 757<a name="math_toolkit.error_handling.h1"></a> 758 <span class="phrase"><a name="math_toolkit.error_handling.rationale"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.rationale">Rationale</a> 759 </h4> 760<p> 761 The flexibility of the current implementation should be reasonably obvious: 762 the default behaviours were chosen based on feedback during the formal review 763 of this library. It was felt that: 764 </p> 765<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 766<li class="listitem"> 767 Genuine errors should be flagged with exceptions rather than following 768 C-compatible behaviour and setting <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code>. 769 </li> 770<li class="listitem"> 771 Numeric underflow and denormalised results were not considered to be fatal 772 errors in most cases, so it was felt that these should be ignored. 773 </li> 774<li class="listitem"> 775 If there is more than one error, only the first detected will be reported 776 in the throw message. 777 </li> 778</ul></div> 779<h4> 780<a name="math_toolkit.error_handling.h2"></a> 781 <span class="phrase"><a name="math_toolkit.error_handling.finding_more_information"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.finding_more_information">Finding 782 More Information</a> 783 </h4> 784<p> 785 There are some pre-processor macro defines that can be used to <a class="link" href="pol_ref/policy_defaults.html" title="Using Macros to Change the Policy Defaults">change 786 the policy defaults</a>. See also the <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">policy section</a>. 787 </p> 788<p> 789 An example is at the Policy tutorial in <a class="link" href="pol_tutorial/changing_policy_defaults.html" title="Changing the Policy Defaults">Changing 790 the Policy Defaults</a>. 791 </p> 792<p> 793 Full source code of this typical example of passing a 'bad' argument (negative 794 degrees of freedom) to Student's t distribution is <a class="link" href="stat_tut/weg/error_eg.html" title="Error Handling Example">in 795 the error handling example</a>. 796 </p> 797<p> 798 The various kind of errors are described in more detail below. 799 </p> 800<h4> 801<a name="math_toolkit.error_handling.h3"></a> 802 <span class="phrase"><a name="math_toolkit.error_handling.domain_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.domain_error">Domain 803 Errors</a> 804 </h4> 805<p> 806 When a special function is passed an argument that is outside the range of 807 values for which that function is defined, then the function returns the result 808 of: 809 </p> 810<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_domain_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <span class="identifier">Val</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 811</pre> 812<p> 813 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating-point 814 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 815 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 816 is an error message describing the problem, Val is the value that was out of 817 range, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> is the current policy in use 818 for the function that was called. 819 </p> 820<p> 821 The default policy behaviour of this function is to throw a std::domain_error 822 C++ exception. But if the <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> is to ignore 823 the error, or set global <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code>, 824 then a NaN will be returned. 825 </p> 826<p> 827 This behaviour is chosen to assist compatibility with the behaviour of <span class="emphasis"><em>ISO/IEC 828 9899:1999 Programming languages - C</em></span> and with the <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf" target="_top">Draft 829 Technical Report on C++ Library Extensions, 2005-06-24, section 5.2.1, paragraph 830 6</a>: 831 </p> 832<div class="blockquote"><blockquote class="blockquote"><p> 833 <span class="emphasis"><em>"Each of the functions declared above shall return a NaN (Not 834 a Number) if any argument value is a NaN, but it shall not report a domain 835 error. Otherwise, each of the functions declared above shall report a domain 836 error for just those argument values for which:<br> the function description's 837 Returns clause explicitly specifies a domain, and those arguments fall outside 838 the specified domain; or <br> the corresponding mathematical function value 839 has a non-zero imaginary component; or <br> the corresponding mathematical 840 function is not mathematically defined. <br> Note 2: A mathematical function 841 is mathematically defined for a given set of argument values if it is explicitly 842 defined for that set of argument values or if its limiting value exists and 843 does not depend on the direction of approach."</em></span> 844 </p></blockquote></div> 845<p> 846 Note that in order to support information-rich error messages when throwing 847 exceptions, <code class="computeroutput"><span class="identifier">Message</span></code> must contain 848 a <a href="../../../../format/index.html" target="_top">Boost.Format</a> recognised format 849 specifier: the argument <code class="computeroutput"><span class="identifier">Val</span></code> 850 is inserted into the error message according to the specifier used. 851 </p> 852<p> 853 For example if <code class="computeroutput"><span class="identifier">Message</span></code> contains 854 a "%1%" then it is replaced by the value of <code class="computeroutput"><span class="identifier">Val</span></code> 855 to the full precision of T, where as "%.3g" would contain the value 856 of <code class="computeroutput"><span class="identifier">Val</span></code> to 3 digits. See the 857 <a href="../../../../format/index.html" target="_top">Boost.Format</a> documentation 858 for more details. 859 </p> 860<h4> 861<a name="math_toolkit.error_handling.h4"></a> 862 <span class="phrase"><a name="math_toolkit.error_handling.pole_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.pole_error">Evaluation 863 at a pole</a> 864 </h4> 865<p> 866 When a special function is passed an argument that is at a pole without a well 867 defined residual value, then the function returns the result of: 868 </p> 869<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_pole_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <span class="identifier">Val</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 870</pre> 871<p> 872 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating point 873 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 874 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 875 is an error message describing the problem, <code class="computeroutput"><span class="identifier">Val</span></code> 876 is the value of the argument that is at a pole, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> 877 is the current policy in use for the function that was called. 878 </p> 879<p> 880 The default behaviour of this function is to throw a std::domain_error exception. 881 But <a class="link" href="pol_ref/error_handling_policies.html" title="Error Handling Policies">error handling 882 policies</a> can be used to change this, for example to <code class="computeroutput"><span class="identifier">ignore_error</span></code> 883 and return NaN. 884 </p> 885<p> 886 Note that in order to support information-rich error messages when throwing 887 exceptions, <code class="computeroutput"><span class="identifier">Message</span></code> must contain 888 a <a href="../../../../format/index.html" target="_top">Boost.Format</a> recognised format 889 specifier: the argument <code class="computeroutput"><span class="identifier">val</span></code> 890 is inserted into the error message according to the specifier used. 891 </p> 892<p> 893 For example if <code class="computeroutput"><span class="identifier">Message</span></code> contains 894 a "%1%" then it is replaced by the value of <code class="computeroutput"><span class="identifier">val</span></code> 895 to the full precision of T, where as "%.3g" would contain the value 896 of <code class="computeroutput"><span class="identifier">val</span></code> to 3 digits. See the 897 <a href="../../../../format/index.html" target="_top">Boost.Format</a> documentation 898 for more details. 899 </p> 900<h4> 901<a name="math_toolkit.error_handling.h5"></a> 902 <span class="phrase"><a name="math_toolkit.error_handling.overflow_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.overflow_error">Numeric 903 Overflow</a> 904 </h4> 905<p> 906 When the result of a special function is too large to fit in the argument floating-point 907 type, then the function returns the result of: 908 </p> 909<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_overflow_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 910</pre> 911<p> 912 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating-point 913 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 914 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 915 is an error message describing the problem, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> 916 is the current policy in use for the function that was called. 917 </p> 918<p> 919 The default policy for this function is that <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">overflow_error</span></code> 920 C++ exception is thrown. But if, for example, an <code class="computeroutput"><span class="identifier">ignore_error</span></code> 921 policy is used, then returns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">infinity</span><span class="special">()</span></code>. 922 In this situation if the type <code class="computeroutput"><span class="identifier">T</span></code> 923 doesn't support infinities, the maximum value for the type is returned. 924 </p> 925<h4> 926<a name="math_toolkit.error_handling.h6"></a> 927 <span class="phrase"><a name="math_toolkit.error_handling.underflow_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.underflow_error">Numeric 928 Underflow</a> 929 </h4> 930<p> 931 If the result of a special function is known to be non-zero, but the calculated 932 result underflows to zero, then the function returns the result of: 933 </p> 934<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_underflow_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 935</pre> 936<p> 937 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating point 938 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 939 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 940 is an error message describing the problem, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> 941 is the current policy in use for the called function. 942 </p> 943<p> 944 The default version of this function returns zero. But with another policy, 945 like <code class="computeroutput"><span class="identifier">throw_on_error</span></code>, throws 946 an <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underflow_error</span></code> C++ exception. 947 </p> 948<h4> 949<a name="math_toolkit.error_handling.h7"></a> 950 <span class="phrase"><a name="math_toolkit.error_handling.denorm_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.denorm_error">Denormalisation 951 Errors</a> 952 </h4> 953<p> 954 If the result of a special function is a denormalised value <span class="emphasis"><em>z</em></span> 955 then the function returns the result of: 956 </p> 957<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_denorm_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 958</pre> 959<p> 960 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating point 961 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 962 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 963 is an error message describing the problem, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> 964 is the current policy in use for the called function. 965 </p> 966<p> 967 The default version of this function returns <span class="emphasis"><em>z</em></span>. But with 968 another policy, like <code class="computeroutput"><span class="identifier">throw_on_error</span></code> 969 throws an <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">underflow_error</span></code> C++ exception. 970 </p> 971<h4> 972<a name="math_toolkit.error_handling.h8"></a> 973 <span class="phrase"><a name="math_toolkit.error_handling.evaluation_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.evaluation_error">Evaluation 974 Errors</a> 975 </h4> 976<p> 977 When a special function calculates a result that is known to be erroneous, 978 or where the result is incalculable then it calls: 979 </p> 980<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_evaluation_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <span class="identifier">Val</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 981</pre> 982<p> 983 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating point 984 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 985 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 986 is an error message describing the problem, <code class="computeroutput"><span class="identifier">Val</span></code> 987 is the erroneous value, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> is the current 988 policy in use for the called function. 989 </p> 990<p> 991 The default behaviour of this function is to throw a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">evaluation_error</span></code>. 992 </p> 993<p> 994 Note that in order to support information rich error messages when throwing 995 exceptions, <code class="computeroutput"><span class="identifier">Message</span></code> must contain 996 a <a href="../../../../format/index.html" target="_top">Boost.Format</a> recognised format 997 specifier: the argument <code class="computeroutput"><span class="identifier">val</span></code> 998 is inserted into the error message according to the specifier used. 999 </p> 1000<p> 1001 For example if <code class="computeroutput"><span class="identifier">Message</span></code> contains 1002 a "%1%" then it is replaced by the value of <code class="computeroutput"><span class="identifier">val</span></code> 1003 to the full precision of T, where as "%.3g" would contain the value 1004 of <code class="computeroutput"><span class="identifier">val</span></code> to 3 digits. See the 1005 <a href="../../../../format/index.html" target="_top">Boost.Format</a> documentation 1006 for more details. 1007 </p> 1008<h4> 1009<a name="math_toolkit.error_handling.h9"></a> 1010 <span class="phrase"><a name="math_toolkit.error_handling.indeterminate_result_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.indeterminate_result_error">Indeterminate 1011 Result Errors</a> 1012 </h4> 1013<p> 1014 When the result of a special function is indeterminate for the value that was 1015 passed to it, then the function returns the result of: 1016 </p> 1017<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_overflow_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <span class="identifier">Val</span><span class="special">,</span> <span class="identifier">Default</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 1018</pre> 1019<p> 1020 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating-point 1021 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 1022 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 1023 is an error message describing the problem, Val is the value for which the 1024 result is indeterminate, Default is an alternative default result that must 1025 be returned for <code class="computeroutput"><span class="identifier">ignore_error</span></code> 1026 and <code class="computeroutput"><span class="identifier">errno_on_erro</span></code> policies, 1027 and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> is the current policy in use for the 1028 function that was called. 1029 </p> 1030<p> 1031 The default policy for this function is <code class="computeroutput"><span class="identifier">ignore_error</span></code>: 1032 note that this error type is reserved for situations where the result is mathematically 1033 undefined or indeterminate, but there is none the less a convention for what 1034 the result should be: for example the C99 standard specifies that the result 1035 of 0<sup>0</sup> is 1, even though the result is actually mathematically indeterminate. 1036 </p> 1037<h4> 1038<a name="math_toolkit.error_handling.h10"></a> 1039 <span class="phrase"><a name="math_toolkit.error_handling.rounding_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.rounding_error">Rounding 1040 Errors</a> 1041 </h4> 1042<p> 1043 When one of the rounding functions <a class="link" href="rounding/round.html" title="Rounding Functions">round</a>, 1044 <a class="link" href="rounding/trunc.html" title="Truncation Functions">trunc</a> or <a class="link" href="rounding/modf.html" title="Integer and Fractional Part Splitting (modf)">modf</a> 1045 is called with an argument that has no integer representation, or is too large 1046 to be represented in the result type then the value returned is the result 1047 of a call to: 1048 </p> 1049<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">raise_rounding_error</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">FunctionName</span><span class="special">,</span> <span class="identifier">Message</span><span class="special">,</span> <span class="identifier">Val</span><span class="special">,</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">);</span> 1050</pre> 1051<p> 1052 Where <code class="computeroutput"><span class="identifier">T</span></code> is the floating point 1053 type passed to the function, <code class="computeroutput"><span class="identifier">FunctionName</span></code> 1054 is the name of the function, <code class="computeroutput"><span class="identifier">Message</span></code> 1055 is an error message describing the problem, <code class="computeroutput"><span class="identifier">Val</span></code> 1056 is the erroneous argument, and <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a> is the 1057 current policy in use for the called function. 1058 </p> 1059<p> 1060 The default behaviour of this function is to throw a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">rounding_error</span></code>. 1061 </p> 1062<p> 1063 Note that in order to support information rich error messages when throwing 1064 exceptions, <code class="computeroutput"><span class="identifier">Message</span></code> must contain 1065 a <a href="../../../../format/index.html" target="_top">Boost.Format</a> recognised format 1066 specifier: the argument <code class="computeroutput"><span class="identifier">val</span></code> 1067 is inserted into the error message according to the specifier used. 1068 </p> 1069<p> 1070 For example if <code class="computeroutput"><span class="identifier">Message</span></code> contains 1071 a "%1%" then it is replaced by the value of <code class="computeroutput"><span class="identifier">val</span></code> 1072 to the full precision of T, where as "%.3g" would contain the value 1073 of <code class="computeroutput"><span class="identifier">val</span></code> to 3 digits. See the 1074 <a href="../../../../format/index.html" target="_top">Boost.Format</a> documentation 1075 for more details. 1076 </p> 1077<h4> 1078<a name="math_toolkit.error_handling.h11"></a> 1079 <span class="phrase"><a name="math_toolkit.error_handling.checked_narrowing_cast"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.checked_narrowing_cast">Errors 1080 from typecasts</a> 1081 </h4> 1082<p> 1083 Many special functions evaluate their results at a higher precision than their 1084 arguments in order to ensure full machine precision in the result: for example, 1085 a function passed a float argument may evaluate its result using double precision 1086 internally. Many of the errors listed above may therefore occur not during 1087 evaluation, but when converting the result to the narrower result type. The 1088 function: 1089 </p> 1090<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <a class="link" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc">Policy</a><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> 1091<span class="identifier">T</span> <span class="identifier">checked_narrowing_cast</span><span class="special">(</span><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">);</span> 1092</pre> 1093<p> 1094 Is used to perform these conversions, and will call the error handlers listed 1095 above on <a class="link" href="error_handling.html#math_toolkit.error_handling.overflow_error">overflow</a>, 1096 <a class="link" href="error_handling.html#math_toolkit.error_handling.underflow_error">underflow</a> 1097 or <a class="link" href="error_handling.html#math_toolkit.error_handling.denorm_error">denormalisation</a>. 1098 </p> 1099</div> 1100<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 1101<td align="left"></td> 1102<td align="right"><div class="copyright-footer">Copyright © 2006-2019 Nikhar 1103 Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, 1104 Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan 1105 Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, 1106 Daryle Walker and Xiaogang Zhang<p> 1107 Distributed under the Boost Software License, Version 1.0. (See accompanying 1108 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 1109 </p> 1110</div></td> 1111</tr></table> 1112<hr> 1113<div class="spirit-nav"> 1114<a accesskey="p" href="result_type.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../overview.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="compilers_overview.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 1115</div> 1116</body> 1117</html> 1118
