1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>buffer</title> 5<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../reference.html" title="Reference"> 9<link rel="prev" href="bind_executor/overload2.html" title="bind_executor (2 of 2 overloads)"> 10<link rel="next" href="buffer/overload1.html" title="buffer (1 of 32 overloads)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> 15<td align="center"><a href="../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="bind_executor/overload2.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="buffer/overload1.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.reference.buffer"></a><a class="link" href="buffer.html" title="buffer">buffer</a> 28</h3></div></div></div> 29<p> 30 <a class="indexterm" name="boost_asio.indexterm.buffer"></a> 31The <code class="computeroutput">boost::asio::buffer</code> function 32 is used to create a buffer object to represent raw memory, an array of POD 33 elements, a vector of POD elements, or a std::string. 34 </p> 35<p> 36 Create a new modifiable buffer from an existing buffer. 37 </p> 38<pre class="programlisting">mutable_buffer <a class="link" href="buffer/overload1.html" title="buffer (1 of 32 overloads)">buffer</a>( 39 const mutable_buffer & b); 40 <span class="emphasis"><em>» <a class="link" href="buffer/overload1.html" title="buffer (1 of 32 overloads)">more...</a></em></span> 41 42mutable_buffer <a class="link" href="buffer/overload2.html" title="buffer (2 of 32 overloads)">buffer</a>( 43 const mutable_buffer & b, 44 std::size_t max_size_in_bytes); 45 <span class="emphasis"><em>» <a class="link" href="buffer/overload2.html" title="buffer (2 of 32 overloads)">more...</a></em></span> 46</pre> 47<p> 48 Create a new non-modifiable buffer from an existing buffer. 49 </p> 50<pre class="programlisting">const_buffer <a class="link" href="buffer/overload3.html" title="buffer (3 of 32 overloads)">buffer</a>( 51 const const_buffer & b); 52 <span class="emphasis"><em>» <a class="link" href="buffer/overload3.html" title="buffer (3 of 32 overloads)">more...</a></em></span> 53 54const_buffer <a class="link" href="buffer/overload4.html" title="buffer (4 of 32 overloads)">buffer</a>( 55 const const_buffer & b, 56 std::size_t max_size_in_bytes); 57 <span class="emphasis"><em>» <a class="link" href="buffer/overload4.html" title="buffer (4 of 32 overloads)">more...</a></em></span> 58</pre> 59<p> 60 Create a new modifiable buffer that represents the given memory range. 61 </p> 62<pre class="programlisting">mutable_buffer <a class="link" href="buffer/overload5.html" title="buffer (5 of 32 overloads)">buffer</a>( 63 void * data, 64 std::size_t size_in_bytes); 65 <span class="emphasis"><em>» <a class="link" href="buffer/overload5.html" title="buffer (5 of 32 overloads)">more...</a></em></span> 66</pre> 67<p> 68 Create a new non-modifiable buffer that represents the given memory range. 69 </p> 70<pre class="programlisting">const_buffer <a class="link" href="buffer/overload6.html" title="buffer (6 of 32 overloads)">buffer</a>( 71 const void * data, 72 std::size_t size_in_bytes); 73 <span class="emphasis"><em>» <a class="link" href="buffer/overload6.html" title="buffer (6 of 32 overloads)">more...</a></em></span> 74</pre> 75<p> 76 Create a new modifiable buffer that represents the given POD array. 77 </p> 78<pre class="programlisting">template< 79 typename PodType, 80 std::size_t N> 81mutable_buffer <a class="link" href="buffer/overload7.html" title="buffer (7 of 32 overloads)">buffer</a>( 82 PodType (&data)[N]); 83 <span class="emphasis"><em>» <a class="link" href="buffer/overload7.html" title="buffer (7 of 32 overloads)">more...</a></em></span> 84 85template< 86 typename PodType, 87 std::size_t N> 88mutable_buffer <a class="link" href="buffer/overload8.html" title="buffer (8 of 32 overloads)">buffer</a>( 89 PodType (&data)[N], 90 std::size_t max_size_in_bytes); 91 <span class="emphasis"><em>» <a class="link" href="buffer/overload8.html" title="buffer (8 of 32 overloads)">more...</a></em></span> 92</pre> 93<p> 94 Create a new non-modifiable buffer that represents the given POD array. 95 </p> 96<pre class="programlisting">template< 97 typename PodType, 98 std::size_t N> 99const_buffer <a class="link" href="buffer/overload9.html" title="buffer (9 of 32 overloads)">buffer</a>( 100 const PodType (&data)[N]); 101 <span class="emphasis"><em>» <a class="link" href="buffer/overload9.html" title="buffer (9 of 32 overloads)">more...</a></em></span> 102 103template< 104 typename PodType, 105 std::size_t N> 106const_buffer <a class="link" href="buffer/overload10.html" title="buffer (10 of 32 overloads)">buffer</a>( 107 const PodType (&data)[N], 108 std::size_t max_size_in_bytes); 109 <span class="emphasis"><em>» <a class="link" href="buffer/overload10.html" title="buffer (10 of 32 overloads)">more...</a></em></span> 110</pre> 111<p> 112 Create a new modifiable buffer that represents the given POD array. 113 </p> 114<pre class="programlisting">template< 115 typename PodType, 116 std::size_t N> 117mutable_buffer <a class="link" href="buffer/overload11.html" title="buffer (11 of 32 overloads)">buffer</a>( 118 boost::array< PodType, N > & data); 119 <span class="emphasis"><em>» <a class="link" href="buffer/overload11.html" title="buffer (11 of 32 overloads)">more...</a></em></span> 120 121template< 122 typename PodType, 123 std::size_t N> 124mutable_buffer <a class="link" href="buffer/overload12.html" title="buffer (12 of 32 overloads)">buffer</a>( 125 boost::array< PodType, N > & data, 126 std::size_t max_size_in_bytes); 127 <span class="emphasis"><em>» <a class="link" href="buffer/overload12.html" title="buffer (12 of 32 overloads)">more...</a></em></span> 128</pre> 129<p> 130 Create a new non-modifiable buffer that represents the given POD array. 131 </p> 132<pre class="programlisting">template< 133 typename PodType, 134 std::size_t N> 135const_buffer <a class="link" href="buffer/overload13.html" title="buffer (13 of 32 overloads)">buffer</a>( 136 boost::array< const PodType, N > & data); 137 <span class="emphasis"><em>» <a class="link" href="buffer/overload13.html" title="buffer (13 of 32 overloads)">more...</a></em></span> 138 139template< 140 typename PodType, 141 std::size_t N> 142const_buffer <a class="link" href="buffer/overload14.html" title="buffer (14 of 32 overloads)">buffer</a>( 143 boost::array< const PodType, N > & data, 144 std::size_t max_size_in_bytes); 145 <span class="emphasis"><em>» <a class="link" href="buffer/overload14.html" title="buffer (14 of 32 overloads)">more...</a></em></span> 146 147template< 148 typename PodType, 149 std::size_t N> 150const_buffer <a class="link" href="buffer/overload15.html" title="buffer (15 of 32 overloads)">buffer</a>( 151 const boost::array< PodType, N > & data); 152 <span class="emphasis"><em>» <a class="link" href="buffer/overload15.html" title="buffer (15 of 32 overloads)">more...</a></em></span> 153 154template< 155 typename PodType, 156 std::size_t N> 157const_buffer <a class="link" href="buffer/overload16.html" title="buffer (16 of 32 overloads)">buffer</a>( 158 const boost::array< PodType, N > & data, 159 std::size_t max_size_in_bytes); 160 <span class="emphasis"><em>» <a class="link" href="buffer/overload16.html" title="buffer (16 of 32 overloads)">more...</a></em></span> 161</pre> 162<p> 163 Create a new modifiable buffer that represents the given POD array. 164 </p> 165<pre class="programlisting">template< 166 typename PodType, 167 std::size_t N> 168mutable_buffer <a class="link" href="buffer/overload17.html" title="buffer (17 of 32 overloads)">buffer</a>( 169 std::array< PodType, N > & data); 170 <span class="emphasis"><em>» <a class="link" href="buffer/overload17.html" title="buffer (17 of 32 overloads)">more...</a></em></span> 171 172template< 173 typename PodType, 174 std::size_t N> 175mutable_buffer <a class="link" href="buffer/overload18.html" title="buffer (18 of 32 overloads)">buffer</a>( 176 std::array< PodType, N > & data, 177 std::size_t max_size_in_bytes); 178 <span class="emphasis"><em>» <a class="link" href="buffer/overload18.html" title="buffer (18 of 32 overloads)">more...</a></em></span> 179</pre> 180<p> 181 Create a new non-modifiable buffer that represents the given POD array. 182 </p> 183<pre class="programlisting">template< 184 typename PodType, 185 std::size_t N> 186const_buffer <a class="link" href="buffer/overload19.html" title="buffer (19 of 32 overloads)">buffer</a>( 187 std::array< const PodType, N > & data); 188 <span class="emphasis"><em>» <a class="link" href="buffer/overload19.html" title="buffer (19 of 32 overloads)">more...</a></em></span> 189 190template< 191 typename PodType, 192 std::size_t N> 193const_buffer <a class="link" href="buffer/overload20.html" title="buffer (20 of 32 overloads)">buffer</a>( 194 std::array< const PodType, N > & data, 195 std::size_t max_size_in_bytes); 196 <span class="emphasis"><em>» <a class="link" href="buffer/overload20.html" title="buffer (20 of 32 overloads)">more...</a></em></span> 197 198template< 199 typename PodType, 200 std::size_t N> 201const_buffer <a class="link" href="buffer/overload21.html" title="buffer (21 of 32 overloads)">buffer</a>( 202 const std::array< PodType, N > & data); 203 <span class="emphasis"><em>» <a class="link" href="buffer/overload21.html" title="buffer (21 of 32 overloads)">more...</a></em></span> 204 205template< 206 typename PodType, 207 std::size_t N> 208const_buffer <a class="link" href="buffer/overload22.html" title="buffer (22 of 32 overloads)">buffer</a>( 209 const std::array< PodType, N > & data, 210 std::size_t max_size_in_bytes); 211 <span class="emphasis"><em>» <a class="link" href="buffer/overload22.html" title="buffer (22 of 32 overloads)">more...</a></em></span> 212</pre> 213<p> 214 Create a new modifiable buffer that represents the given POD vector. 215 </p> 216<pre class="programlisting">template< 217 typename PodType, 218 typename Allocator> 219mutable_buffer <a class="link" href="buffer/overload23.html" title="buffer (23 of 32 overloads)">buffer</a>( 220 std::vector< PodType, Allocator > & data); 221 <span class="emphasis"><em>» <a class="link" href="buffer/overload23.html" title="buffer (23 of 32 overloads)">more...</a></em></span> 222 223template< 224 typename PodType, 225 typename Allocator> 226mutable_buffer <a class="link" href="buffer/overload24.html" title="buffer (24 of 32 overloads)">buffer</a>( 227 std::vector< PodType, Allocator > & data, 228 std::size_t max_size_in_bytes); 229 <span class="emphasis"><em>» <a class="link" href="buffer/overload24.html" title="buffer (24 of 32 overloads)">more...</a></em></span> 230</pre> 231<p> 232 Create a new non-modifiable buffer that represents the given POD vector. 233 </p> 234<pre class="programlisting">template< 235 typename PodType, 236 typename Allocator> 237const_buffer <a class="link" href="buffer/overload25.html" title="buffer (25 of 32 overloads)">buffer</a>( 238 const std::vector< PodType, Allocator > & data); 239 <span class="emphasis"><em>» <a class="link" href="buffer/overload25.html" title="buffer (25 of 32 overloads)">more...</a></em></span> 240 241template< 242 typename PodType, 243 typename Allocator> 244const_buffer <a class="link" href="buffer/overload26.html" title="buffer (26 of 32 overloads)">buffer</a>( 245 const std::vector< PodType, Allocator > & data, 246 std::size_t max_size_in_bytes); 247 <span class="emphasis"><em>» <a class="link" href="buffer/overload26.html" title="buffer (26 of 32 overloads)">more...</a></em></span> 248</pre> 249<p> 250 Create a new modifiable buffer that represents the given string. 251 </p> 252<pre class="programlisting">template< 253 typename Elem, 254 typename Traits, 255 typename Allocator> 256mutable_buffer <a class="link" href="buffer/overload27.html" title="buffer (27 of 32 overloads)">buffer</a>( 257 std::basic_string< Elem, Traits, Allocator > & data); 258 <span class="emphasis"><em>» <a class="link" href="buffer/overload27.html" title="buffer (27 of 32 overloads)">more...</a></em></span> 259 260template< 261 typename Elem, 262 typename Traits, 263 typename Allocator> 264mutable_buffer <a class="link" href="buffer/overload28.html" title="buffer (28 of 32 overloads)">buffer</a>( 265 std::basic_string< Elem, Traits, Allocator > & data, 266 std::size_t max_size_in_bytes); 267 <span class="emphasis"><em>» <a class="link" href="buffer/overload28.html" title="buffer (28 of 32 overloads)">more...</a></em></span> 268</pre> 269<p> 270 Create a new non-modifiable buffer that represents the given string. 271 </p> 272<pre class="programlisting">template< 273 typename Elem, 274 typename Traits, 275 typename Allocator> 276const_buffer <a class="link" href="buffer/overload29.html" title="buffer (29 of 32 overloads)">buffer</a>( 277 const std::basic_string< Elem, Traits, Allocator > & data); 278 <span class="emphasis"><em>» <a class="link" href="buffer/overload29.html" title="buffer (29 of 32 overloads)">more...</a></em></span> 279 280template< 281 typename Elem, 282 typename Traits, 283 typename Allocator> 284const_buffer <a class="link" href="buffer/overload30.html" title="buffer (30 of 32 overloads)">buffer</a>( 285 const std::basic_string< Elem, Traits, Allocator > & data, 286 std::size_t max_size_in_bytes); 287 <span class="emphasis"><em>» <a class="link" href="buffer/overload30.html" title="buffer (30 of 32 overloads)">more...</a></em></span> 288</pre> 289<p> 290 Create a new modifiable buffer that represents the given string_view. 291 </p> 292<pre class="programlisting">template< 293 typename Elem, 294 typename Traits> 295const_buffer <a class="link" href="buffer/overload31.html" title="buffer (31 of 32 overloads)">buffer</a>( 296 basic_string_view< Elem, Traits > data); 297 <span class="emphasis"><em>» <a class="link" href="buffer/overload31.html" title="buffer (31 of 32 overloads)">more...</a></em></span> 298</pre> 299<p> 300 Create a new non-modifiable buffer that represents the given string. 301 </p> 302<pre class="programlisting">template< 303 typename Elem, 304 typename Traits> 305const_buffer <a class="link" href="buffer/overload32.html" title="buffer (32 of 32 overloads)">buffer</a>( 306 basic_string_view< Elem, Traits > data, 307 std::size_t max_size_in_bytes); 308 <span class="emphasis"><em>» <a class="link" href="buffer/overload32.html" title="buffer (32 of 32 overloads)">more...</a></em></span> 309</pre> 310<p> 311 A buffer object represents a contiguous region of memory as a 2-tuple consisting 312 of a pointer and size in bytes. A tuple of the form <code class="computeroutput">{void*, size_t}</code> 313 specifies a mutable (modifiable) region of memory. Similarly, a tuple of 314 the form <code class="computeroutput">{const void*, size_t}</code> specifies a const (non-modifiable) 315 region of memory. These two forms correspond to the classes <a class="link" href="mutable_buffer.html" title="mutable_buffer"><code class="computeroutput">mutable_buffer</code></a> 316 and <a class="link" href="const_buffer.html" title="const_buffer"><code class="computeroutput">const_buffer</code></a>, 317 respectively. To mirror C++'s conversion rules, a <a class="link" href="mutable_buffer.html" title="mutable_buffer"><code class="computeroutput">mutable_buffer</code></a> 318 is implicitly convertible to a <a class="link" href="const_buffer.html" title="const_buffer"><code class="computeroutput">const_buffer</code></a>, 319 and the opposite conversion is not permitted. 320 </p> 321<p> 322 The simplest use case involves reading or writing a single buffer of a specified 323 size: 324 </p> 325<pre class="programlisting">sock.send(boost::asio::buffer(data, size)); 326</pre> 327<p> 328 In the above example, the return value of <code class="computeroutput">boost::asio::buffer</code> 329 meets the requirements of the ConstBufferSequence concept so that it may 330 be directly passed to the socket's write function. A buffer created for modifiable 331 memory also meets the requirements of the MutableBufferSequence concept. 332 </p> 333<p> 334 An individual buffer may be created from a builtin array, std::vector, std::array 335 or boost::array of POD elements. This helps prevent buffer overruns by automatically 336 determining the size of the buffer: 337 </p> 338<pre class="programlisting">char d1[128]; 339size_t bytes_transferred = sock.receive(boost::asio::buffer(d1)); 340 341std::vector<char> d2(128); 342bytes_transferred = sock.receive(boost::asio::buffer(d2)); 343 344std::array<char, 128> d3; 345bytes_transferred = sock.receive(boost::asio::buffer(d3)); 346 347boost::array<char, 128> d4; 348bytes_transferred = sock.receive(boost::asio::buffer(d4)); 349</pre> 350<p> 351 In all three cases above, the buffers created are exactly 128 bytes long. 352 Note that a vector is <span class="emphasis"><em>never</em></span> automatically resized when 353 creating or using a buffer. The buffer size is determined using the vector's 354 <code class="computeroutput">size()</code> member function, and not its capacity. 355 </p> 356<h5> 357<a name="boost_asio.reference.buffer.h0"></a> 358 <span class="phrase"><a name="boost_asio.reference.buffer.accessing_buffer_contents"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.accessing_buffer_contents">Accessing 359 Buffer Contents</a> 360 </h5> 361<p> 362 The contents of a buffer may be accessed using the <code class="computeroutput">data()</code> and 363 <code class="computeroutput">size()</code> member functions: 364 </p> 365<pre class="programlisting">boost::asio::mutable_buffer b1 = ...; 366std::size_t s1 = b1.size(); 367unsigned char* p1 = static_cast<unsigned char*>(b1.data()); 368 369boost::asio::const_buffer b2 = ...; 370std::size_t s2 = b2.size(); 371const void* p2 = b2.data(); 372</pre> 373<p> 374 The <code class="computeroutput">data()</code> member function permits violations of type safety, 375 so uses of it in application code should be carefully considered. 376 </p> 377<p> 378 For convenience, a <a class="link" href="buffer_size.html" title="buffer_size"><code class="computeroutput">buffer_size</code></a> 379 function is provided that works with both buffers and buffer sequences (that 380 is, types meeting the ConstBufferSequence or MutableBufferSequence type requirements). 381 In this case, the function returns the total size of all buffers in the sequence. 382 </p> 383<h5> 384<a name="boost_asio.reference.buffer.h1"></a> 385 <span class="phrase"><a name="boost_asio.reference.buffer.buffer_copying"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.buffer_copying">Buffer 386 Copying</a> 387 </h5> 388<p> 389 The <a class="link" href="buffer_copy.html" title="buffer_copy"><code class="computeroutput">buffer_copy</code></a> 390 function may be used to copy raw bytes between individual buffers and buffer 391 sequences. 392 </p> 393<p> 394 In particular, when used with the <a class="link" href="buffer_size.html" title="buffer_size"><code class="computeroutput">buffer_size</code></a> 395 function, the <a class="link" href="buffer_copy.html" title="buffer_copy"><code class="computeroutput">buffer_copy</code></a> 396 function can be used to linearise a sequence of buffers. For example: 397 </p> 398<pre class="programlisting">vector<const_buffer> buffers = ...; 399 400vector<unsigned char> data(boost::asio::buffer_size(buffers)); 401boost::asio::buffer_copy(boost::asio::buffer(data), buffers); 402</pre> 403<p> 404 Note that <a class="link" href="buffer_copy.html" title="buffer_copy"><code class="computeroutput">buffer_copy</code></a> 405 is implemented in terms of <code class="computeroutput">memcpy</code>, and consequently it cannot 406 be used to copy between overlapping memory regions. 407 </p> 408<h5> 409<a name="boost_asio.reference.buffer.h2"></a> 410 <span class="phrase"><a name="boost_asio.reference.buffer.buffer_invalidation"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.buffer_invalidation">Buffer 411 Invalidation</a> 412 </h5> 413<p> 414 A buffer object does not have any ownership of the memory it refers to. It 415 is the responsibility of the application to ensure the memory region remains 416 valid until it is no longer required for an I/O operation. When the memory 417 is no longer available, the buffer is said to have been invalidated. 418 </p> 419<p> 420 For the <code class="computeroutput">boost::asio::buffer</code> overloads that accept an argument 421 of type std::vector, the buffer objects returned are invalidated by any vector 422 operation that also invalidates all references, pointers and iterators referring 423 to the elements in the sequence (C++ Std, 23.2.4) 424 </p> 425<p> 426 For the <code class="computeroutput">boost::asio::buffer</code> overloads that accept an argument 427 of type std::basic_string, the buffer objects returned are invalidated according 428 to the rules defined for invalidation of references, pointers and iterators 429 referring to elements of the sequence (C++ Std, 21.3). 430 </p> 431<h5> 432<a name="boost_asio.reference.buffer.h3"></a> 433 <span class="phrase"><a name="boost_asio.reference.buffer.buffer_arithmetic"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.buffer_arithmetic">Buffer 434 Arithmetic</a> 435 </h5> 436<p> 437 Buffer objects may be manipulated using simple arithmetic in a safe way which 438 helps prevent buffer overruns. Consider an array initialised as follows: 439 </p> 440<pre class="programlisting">boost::array<char, 6> a = { 'a', 'b', 'c', 'd', 'e' }; 441</pre> 442<p> 443 A buffer object <code class="computeroutput">b1</code> created using: 444 </p> 445<pre class="programlisting">b1 = boost::asio::buffer(a); 446</pre> 447<p> 448 represents the entire array, <code class="computeroutput">{ 'a', 'b', 'c', 'd', 'e' }</code>. An 449 optional second argument to the <code class="computeroutput">boost::asio::buffer</code> function 450 may be used to limit the size, in bytes, of the buffer: 451 </p> 452<pre class="programlisting">b2 = boost::asio::buffer(a, 3); 453</pre> 454<p> 455 such that <code class="computeroutput">b2</code> represents the data <code class="computeroutput">{ 'a', 'b', 'c' }</code>. 456 Even if the size argument exceeds the actual size of the array, the size 457 of the buffer object created will be limited to the array size. 458 </p> 459<p> 460 An offset may be applied to an existing buffer to create a new one: 461 </p> 462<pre class="programlisting">b3 = b1 + 2; 463</pre> 464<p> 465 where <code class="computeroutput">b3</code> will set to represent <code class="computeroutput">{ 'c', 'd', 'e' }</code>. 466 If the offset exceeds the size of the existing buffer, the newly created 467 buffer will be empty. 468 </p> 469<p> 470 Both an offset and size may be specified to create a buffer that corresponds 471 to a specific range of bytes within an existing buffer: 472 </p> 473<pre class="programlisting">b4 = boost::asio::buffer(b1 + 1, 3); 474</pre> 475<p> 476 so that <code class="computeroutput">b4</code> will refer to the bytes <code class="computeroutput">{ 'b', 'c', 'd' }</code>. 477 </p> 478<h5> 479<a name="boost_asio.reference.buffer.h4"></a> 480 <span class="phrase"><a name="boost_asio.reference.buffer.buffers_and_scatter_gather_i_o"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.buffers_and_scatter_gather_i_o">Buffers 481 and Scatter-Gather I/O</a> 482 </h5> 483<p> 484 To read or write using multiple buffers (i.e. scatter-gather I/O), multiple 485 buffer objects may be assigned into a container that supports the MutableBufferSequence 486 (for read) or ConstBufferSequence (for write) concepts: 487 </p> 488<pre class="programlisting">char d1[128]; 489std::vector<char> d2(128); 490boost::array<char, 128> d3; 491 492boost::array<mutable_buffer, 3> bufs1 = { 493 boost::asio::buffer(d1), 494 boost::asio::buffer(d2), 495 boost::asio::buffer(d3) }; 496bytes_transferred = sock.receive(bufs1); 497 498std::vector<const_buffer> bufs2; 499bufs2.push_back(boost::asio::buffer(d1)); 500bufs2.push_back(boost::asio::buffer(d2)); 501bufs2.push_back(boost::asio::buffer(d3)); 502bytes_transferred = sock.send(bufs2); 503</pre> 504<h5> 505<a name="boost_asio.reference.buffer.h5"></a> 506 <span class="phrase"><a name="boost_asio.reference.buffer.requirements"></a></span><a class="link" href="buffer.html#boost_asio.reference.buffer.requirements">Requirements</a> 507 </h5> 508<p> 509 <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/buffer.hpp</code> 510 </p> 511<p> 512 <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code> 513 </p> 514</div> 515<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 516<td align="left"></td> 517<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 518 Kohlhoff<p> 519 Distributed under the Boost Software License, Version 1.0. (See accompanying 520 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>) 521 </p> 522</div></td> 523</tr></table> 524<hr> 525<div class="spirit-nav"> 526<a accesskey="p" href="bind_executor/overload2.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="buffer/overload1.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 527</div> 528</body> 529</html> 530
