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) |
| ap | - | an instance of the va_list type |
| parmN | - | the named parameter preceding the first variable parameter |
(none).
#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
| 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 |
|
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