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1.. title:: clang-tidy - misc-definitions-in-headers
2
3misc-definitions-in-headers
4===========================
5
6Finds non-extern non-inline function and variable definitions in header files,
7which can lead to potential ODR violations in case these headers are included
8from multiple translation units.
9
10.. code-block:: c++
11
12   // Foo.h
13   int a = 1; // Warning: variable definition.
14   extern int d; // OK: extern variable.
15
16   namespace N {
17     int e = 2; // Warning: variable definition.
18   }
19
20   // Warning: variable definition.
21   const char* str = "foo";
22
23   // OK: internal linkage variable definitions are ignored for now.
24   // Although these might also cause ODR violations, we can be less certain and
25   // should try to keep the false-positive rate down.
26   static int b = 1;
27   const int c = 1;
28   const char* const str2 = "foo";
29   constexpr int k = 1;
30
31   // Warning: function definition.
32   int g() {
33     return 1;
34   }
35
36   // OK: inline function definition is allowed to be defined multiple times.
37   inline int e() {
38     return 1;
39   }
40
41   class A {
42   public:
43     int f1() { return 1; } // OK: implicitly inline member function definition is allowed.
44     int f2();
45
46     static int d;
47   };
48
49   // Warning: not an inline member function definition.
50   int A::f2() { return 1; }
51
52   // OK: class static data member declaration is allowed.
53   int A::d = 1;
54
55   // OK: function template is allowed.
56   template<typename T>
57   T f3() {
58     T a = 1;
59     return a;
60   }
61
62   // Warning: full specialization of a function template is not allowed.
63   template <>
64   int f3() {
65     int a = 1;
66     return a;
67   }
68
69   template <typename T>
70   struct B {
71     void f1();
72   };
73
74   // OK: member function definition of a class template is allowed.
75   template <typename T>
76   void B<T>::f1() {}
77
78   class CE {
79     constexpr static int i = 5; // OK: inline variable definition.
80   };
81
82   inline int i = 5; // OK: inline variable definition.
83
84   constexpr int f10() { return 0; } // OK: constexpr function implies inline.
85
86   // OK: C++14 variable templates are inline.
87   template <class T>
88   constexpr T pi = T(3.1415926L);
89
90Options
91-------
92
93.. option:: HeaderFileExtensions
94
95   A comma-separated list of filename extensions of header files (the filename
96   extensions should not include "." prefix). Default is "h,hh,hpp,hxx".
97   For header files without an extension, use an empty string (if there are no
98   other desired extensions) or leave an empty element in the list. e.g.,
99   "h,hh,hpp,hxx," (note the trailing comma).
100
101.. option:: UseHeaderFileExtension
102
103   When `true`, the check will use the file extension to distinguish header
104   files. Default is `true`.
105