Format
#include <stdarg.h> var_type va_arg(va_list arg_ptr, var_type); void va_end(va_list arg_ptr); void va_start(va_list arg_ptr, variable_name);
Language Level: ANSI
Threadsafe: Yes.
Description
The va_arg(), va_end(), and va_start() functions access the arguments to a function when it takes a fixed number of required arguments and a variable number of optional arguments. You declare required arguments as ordinary parameters to the function and access the arguments through the parameter names.
va_start() initializes the arg_ptr pointer for subsequent calls to va_arg() and va_end().
The argument variable_name is the identifier of the rightmost named parameter in the parameter list (preceding , ...). Use va_start() before va_arg(). Corresponding va_start() and va_end() macros must be in the same function.
The va_arg() function retrieves a value of the given var_type from the location given by arg_ptr, and increases arg_ptr to point to the next argument in the list. The va_arg() function can retrieve arguments from the list any number of times within the function. The var_type argument must be one of int, long, decimal, double, struct, union, or pointer, or a typedef of one of these types.
The va_end() function is needed to indicate the end of parameter scanning.
Return Value
The va_arg() function returns the current argument. The va_end and va_start() functions do not return a value.
Example that uses va_arg() - va_end() - va_start()
This example passes a variable number of arguments to a function, stores each argument in an array, and prints each argument.
#include <stdio.h> #include <stdarg.h> int vout(int max, ...); int main(void) { vout(3, "Sat", "Sun", "Mon"); printf("\n"); vout(5, "Mon", "Tues", "Wed", "Thurs", "Fri"); } int vout(int max, ...) { va_list arg_ptr; int args = 0; char *days[7]; va_start(arg_ptr, max); while(args < max) { days[args] = va_arg(arg_ptr, char *); printf("Day: %s \n", days[args++]); } va_end(arg_ptr); } /****************** Output should be similar to: **************** Day: Sat Day: Sun Day: Mon Day: Mon Day: Tues Day: Wed Day: Thurs Day: Fri */
Related Information
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