va_start
|
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) |
Parameters
| ap | - | an instance of the va_list type |
| parmN | - | the named parameter preceding the first variable parameter |
Expanded value
(none)
Example
#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
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
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
|
|