C <stdarg.h> - va_start
The C <stdarg.h> va_start macro enables access to the additional arguments following the named argument parm_n.
va_start should be invoked first with the list of variable arguments as a va_list before any calls to va_arg. After the call, it carries the information needed to retrieve the additional arguments using va_arg. A function that invokes va_start, shall also invoke va_end before it returns.
Syntax
void va_start( va_list ap, parm_n );
Parameters
ap |
Specify an instance of the va_list type. |
parm_n |
Specify the named parameter preceding the first variable parameter. The arguments extracted by subsequent calls to va_arg are those after parm_n.
If this parameter is declared with register storage class, with function or array type, or with a type that is not compatible with the type that results after application of the default argument promotions, the behavior is undefined. |
Return Value
None.
Example:
The example below shows the usage of va_start macro function.
#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 () {
printf("Sum is: %d\n", add_nums (2, 10, 20));
printf("Sum is: %d\n", add_nums (3, 10, 20, 30));
printf("Sum is: %d\n", add_nums (4, 10, 20, 30, 40));
return 0;
}
The output of the above code will be:
Sum is: 30 Sum is: 60 Sum is: 100
❮ C <stdarg.h> Library
