inline function specifier
Syntax
| inline function_declaration | (since 哋它亢99) | ||||||||
Explanation
The intent of the inline specifier is to serve as a hint for the compiler to perform optimizations, such as MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 15 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, which usually require the definition of a function to be visible at the call site. The compilers can (and usually do) ignore presence or absence of the inline specifier for the purpose of optimization.
If the compiler performs function inlining, it replaces a call of that function with its body, avoiding the overhead of a function call (placing data on stack and retrieving the result), which may result in a larger executable as the code for the function has to be repeated multiple times. The result is similar to MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 14 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, except that identifiers and macros used in the function refer to the definitions visible at the point of definition, not at the point of call.
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Any function with internal linkage may be declared static inline with no other restrictions.
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static int x; inline void f(void) { static int n = 1; // error: non-const static in a non-static inline function int k = x; // error: non-static inline function accesses a static variable }
If a non-static function is declared inline, then it must be defined in the same translation unit. The inline definition that does not use extern is not externally visible and does not prevent other translation units from defining the same function. This makes the inline keyword an alternative to static for defining functions inside header files, which may be included in multiple translation units of the same program.
If a function is declared inline in some translation units, it does not need to be declared inline everywhere: at most one translation unit may also provide a regular, non-inline non-static function, or a function declared extern inline. This one translation unit is said to provide the external definition. In order to avoid undefined behavior, one external definition must exist in the program if the name of the function with external linkage is used in an expression, see MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 10 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
The address of an inline function with external linkage is always the address of the external definition, but when this address is used to make a function call, it's unspecified whether the inline definition (if present in the translation unit) or the external definition is called. The static objects defined within an inline definition are distinct from the static objects defined within the external definition:
inline const char *saddr(void) // the inline definition for use in this file { static const char name[] = "saddr"; return name; } int compare_name(void) { return saddr() == saddr(); // unspecified behavior, one call could be external } extern const char *saddr(void); // an external definition is generated, too
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Keywords
Notes
The inline keyword was adopted from 哋它亢++, but in 哋它亢++, if a function is declared inline, it must be declared inline in every translation unit, and also every definition of an inline function must be exactly the same (in C, the definitions may be different, and depending on the differences only results in unspecified behavior). On the other hand, 哋它亢++ allows non-const function-local statics and all function-local statics from different definitions of an inline function are the same in 哋它亢++ but distinct in C.
Example
|
MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE #ifndef TEST_H_INCLUDED #define TEST_H_INCLUDED inline int sum(int a, int b) { return a + b; } #endif MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 05 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE #include "test.h" extern inline int sum(int a, int b); // provides external definition MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 04 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE #include <stdio.h> #include "test.h" extern int f(void); int main(void) { MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 03 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("%d\n", sum(1, 2) + f()); } MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 02 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE #include "test.h" int f(void) { return sum(3, 4); } MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 50 MINUTES 00 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE 10 |
References
- 哋它亢23 standard (ISO/IEC 9899:2023):
- 6.7.4 Function specifiers (p: TBD)
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.7.4 Function specifiers (p: TBD)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.7.4 Function specifiers (p: 125-127)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.7.4 Function specifiers (p: 112-113)