C Language: va_start function
(Fetch Argument from Variable Argument List)
In the C Programming Language, the va_start function initializes the variable argument list referred to by ap. The va_start function must be called before using the va_arg function.
Syntax
The syntax for the va_start function in the C Language is:
void va_start(va_list ap, parmN);
Parameters or Arguments
- ap
- A variable argument list.
- parmN
- The name of the last ordinary parameter.
Returns
The va_start function does not return anything.
Required Header
In the C Language, the required header for the va_start function is:
#include <stdarg.h>
Applies To
In the C Language, the va_start function can be used in the following versions:
- ANSI/ISO 9899-1990
va_start Example
/* Example using va_start by TechOnTheNet.com */
#include <stdio.h>
#include <stdarg.h>
int add(int n, ...)
{
/* Define temporary variables */
va_list list;
int total;
/* Initialize total */
total = 0;
/* Set where the variable length part of the argument list ends */
va_start(list, n);
/* Loop through each argument adding the int values */
for (int i=0; i < n; i++)
total = total + va_arg(list, int);
/* Clean up */
va_end(list);
/* Return the calculated total */
return total;
}
int main(int argc, const char * argv[])
{
/* Define temporary variables */
int value1, value2, value3;
int result;
value1 = 3;
value2 = 4;
value3 = 5;
/* Call the add function */
result = add(4, value1, value2, value3);
/* Display the results of the additon */
printf("The sum of %d, %d and %d is %d\n", value1, value2, value3, result);
return 0;
}
When compiled and run, this application will output:
The sum of 3, 4 and 5 is 12
See Also
Other C functions that are noteworthy when dealing with the va_start function:
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