va_start
From cppreference.com
Defined in header <stdarg.h>
|
||
void va_start( va_list ap, parmN ); |
(until C23) | |
void va_start( va_list ap, ... ); |
(since C23) | |
The va_start
macro enables access to the variable arguments following the named argument parmN
(until C23).
va_start
shall be invoked with an instance to a valid va_list object ap
before any calls to va_arg.
If |
(until C23) |
Only the first argument passed to |
(since C23) |
Contents |
[edit] Parameters
ap | - | an instance of the va_list type |
parmN | - | the named parameter preceding the first variable parameter |
[edit] Expanded value
(none)
[edit] Example
Run this code
#include <stdio.h> #include <stdarg.h> int add_nums_C99(int count, ...) { int result = 0; va_list args; va_start(args, count); // count can be omitted since C23 for (int i = 0; i < count; ++i) { result += va_arg(args, int); } va_end(args); return result; } #if __STDC_VERSION__ > 201710L // Same as above, valid since C23 int add_nums_C23(...) { int result = 0; va_list args; va_start(args); int count = va_arg(args, int); for (int i = 0; i < count; ++i) { result += va_arg(args, int); } va_end(args); return result; } #endif int main(void) { printf("%d\n", add_nums_C99(4, 25, 25, 50, 50)); #if __STDC_VERSION__ > 201710L printf("%d\n", add_nums_C23(4, 25, 25, 50, 50)); #endif }
Possible output:
150 150
[edit] References
- C17 standard (ISO/IEC 9899:2018):
- 7.16.1.4 The va_start macro (p: 198-199)
- C11 standard (ISO/IEC 9899:2011):
- 7.16.1.4 The va_start macro (p: 271-272)
- C99 standard (ISO/IEC 9899:1999):
- 7.15.1.4 The va_start macro (p: 251-252)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.8.1.1 The va_start macro
[edit] See also
accesses the next variadic function argument (function macro) | |
(C99) |
makes a copy of the variadic function arguments (function macro) |
ends traversal of the variadic function arguments (function macro) | |
holds the information needed by va_start, va_arg, va_end, and va_copy (typedef) | |
C++ documentation for va_start
|