Can we pass variable number of arguments to a function in c?
5 Answers
Here is an example:
#include <stdlib.h>
#include <stdarg.h>
#include <stdio.h>
int maxof(int, ...) ;
void f(void);
int main(void){
f();
exit(EXIT SUCCESS);
}
int maxof(int n_args, ...){
register int i;
int max, a;
va_list ap;
va_start(ap, n_args);
max = va_arg(ap, int);
for(i = 2; i <= n_args; i++) {
if((a = va_arg(ap, int)) > max)
max = a;
}
va_end(ap);
return max;
}
void f(void) {
int i = 5;
int j[256];
j[42] = 24;
printf("%d\n", maxof(3, i, j[42], 0));
}
2 Comments
haroldcampbell
I don't get the use of the
register here?
Peter
The use of
register is evidence that the code sample is quite old. Use of register is a hint to the compiler to place the variable into a machine register, as a performance optimisation. The majority of C compilers over the last 30 years have ignored that hint, since they can do a better job of register allocation than most programmers can. Nowadays, register has few effects other than forbidding calculation of the address of a variable.If it is a function that accepts a variable number of arguments, yes.
Comments
Yes, if the function accepts variable arguments. If you need to make your own variable-argument function, there are macros that begin with va_ which give you access to the arguments.
Comments
make sure that the variable argument list should always be at the end of the argument list
example: void func(float a, int b, ...) is correct
but void func(float a, ..., int b) is not valid
1 Comment
Jonathan Leffler
Yes, but this is more of a comment than an answer. Certainly, you've explained one aspect, but it is a very minor aspect of the answer.
"You should consider that using variadic functions (C-style) is a dangerous flaw," says Stephane Rolland. You can find his helpful post here.
1 Comment
Alok Save
I believe the advice is for writing your own custom variadic functions in C++ and not for the ones provided by the standard library. Just, imagine life without
printf!
printf?