va_start
Defined in header <stdarg.h>
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The va_start
macro enables access to the variable arguments following the named argument parmN
.
va_start
should be invoked with an instance to a valid va_list
object ap
before any calls to va_arg
.
If parmN
is declared with register
storage class specifier, with an array type, with a function type, or with a type not compatible with the type that results from default argument promotions, the behavior is undefined.
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(int count, ...)
{
int result = 0;
va_list args;
va_start(args, count);
for (int i = 0; i < count; ++i) {
result += va_arg(args, int);
}
va_end(args);
return result;
}
int main(void)
{
printf("%d\n", add_nums(4, 25, 25, 50, 50));
}
Possible output:
150
References
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) |
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