inline specifier
Declares an inline function.
Contents |
[edit] Syntax
inline function_declaration | (1) | ||||||||
class { function_definition };
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(2) | ||||||||
constexpr function_declaration | (3) | (since C++11) | |||||||
[edit] Description
An inline function is a function with the following properties:
The intent of the inline
keyword is to serve as an indicator to the optimizer that inline substitution of the function is preferred over function call, that is, instead of executing the call CPU instruction to transfer control to the function body, a copy of the function body is executed without generating the call. This avoids extra overhead created by the function call (copying the arguments and retrieving the result) but it may result in a larger executable as the code for the function has to be repeated multiple times.
Since this meaning of the keyword inline is non-binding, compilers are free to use inline substitution for any function that's not marked inline, and are free to generate function calls to any function marked inline. Those choices do not change the rules regarding multiple definitions and shared statics listed above.
[edit] Notes
If an inline function is defined differently in different translation units, the behavior is undefined.
The inline specifier cannot be used with a function declaration at block scope (inside another function)
The inline specifier cannot re-declare a function that was already defined in the translation unit as non-inline.
The implicitly-generated member functions and any member function declared as deleted are inline just like any other function defined inside a class definition.
If an inline function is declared in different translation units, the accumulated sets of default arguments must be the same at the end of each translation unit.
[edit] Example
// header file #ifndef EXAMPLE_H #define EXAMPLE_H // function included in multiple source files must be inline inline int sum(int a, int b) { return a + b; } #endif // source file #2 #include "example.h" int a() { return sum(1, 2); } // source file #1 #include "example.h" int b() { return sum(3, 4); }