I would like to make a function that can take a variable number of parameters at once to do something like this:
void function(char *args[]){ ... }
int main(){
function("a","b","c");
}
1 Answer
You are looking for Variadic functions.
Check this example:
#include <stdio.h>
#include <stdarg.h>
double average(int num, ...) {
va_list valist;
double sum = 0.0;
int i;
/* initialize valist for num number of arguments */
va_start(valist, num);
/* access all the arguments assigned to valist */
for (i = 0; i < num; i++) {
sum += va_arg(valist, int);
}
/* clean memory reserved for valist */
va_end(valist);
return sum/num;
}
int main(void) {
printf("Average of 2, 3, 4, 5 = %f\n", average(4, 2, 3, 4, 5));
printf("Average of 5, 10, 15 = %f\n", average(3, 5, 10, 15));
}
Output:
Average of 2, 3, 4, 5 = 3.500000
Average of 5, 10, 15 = 10.000000
Read more in Variadic Functions in C and the Reference.
Tip: Think twice before using Variadic functions. As @user694733 commented, they have no compile time type safety or protection against invalid number of arguments. They can usually be avoided with better program design.
4 Comments
user694733
This answer is correct, but I would like to give standard warning: Do not use variadic functions unless absolutely necessary! They have no compile time type safety or protection against invalid number of arguments. They can usually be avoided with better program design.
gsamaras
@user694733 good advice, thank you! I've updated my answer including a reference too. ;)
Steve Summit
@user694733 Me, I'd say your comment is the logical equivalent of Do not use a chainsaw unless absolutely necessary! I mean, yes, chainsaws are dangerous, and yet, they exist.
user694733
@SteveSummit More like: regular functions are standard chainsaws, and variadic function is chainsaw with slightly sharper teeth, but it's always on and emergency brake has been removed. In my experience, variadic functions seem like good idea at first, but end up being replaced with little less convenient but safer alternatives sooner or later. Only exception is perhaps printf-like logging functions, but even those are often used with special compiler pragmas to enable extra argument validation.
functionto know that there are three arguments this time.