I'm trying to modify an array via variable arguments by passing values of va_arg to the array but for some reason it gives weird results, Here is the code:
#include <stdio.h>
#include <stdarg.h>
void get_args(double* args, int argc, ...);
void get_args(double* args, int argc, ...) {
va_list argv;
va_start(argv, argc);
if (argc == 1) {
args[0] = va_arg(argv, double);
}
else if (argc == 4) {
for (int i = 0; i < argc; i++) {
args[i] = va_arg(argv, double);
}
}
va_end(argv);
}
int main(void) {
double args[4] = { 0, 0, 0, 0 };
get_args(args, 4, 0, 1, 2, 3);
for (int i = 0; i < 4; i++) {
printf("args[%d] = %f\n", i, args[i]);
}
return 0;
}
On Visual Studio (MSVC) it gives following:
args[0] = 0.000000
args[1] = 0.000000
args[2] = 0.000000
args[3] = -92559592143668871097826611732759620974286504571030640424648704.000000
On GCC it gives following:
args[0] = 0.000000
args[1] = 0.000000
args[2] = 0.000000
args[3] = 0.000000
Anyone knows what the mistake i done?
The types of the variadic arguments don't match the type given to va_arg.
The arguments you're passing to get_args i.e. 0, 1, 2, 3 are all of type int, but you're using type double when you try to retrieve them with va_arg. This is a type mismatch which triggers undefined behavior.
Either pass arguments that have type double:
get_args(args, 4, 0.0, 1.0, 2.0, 3.0);
Or use int to pull the arguments off:
args[i] = va_arg(argv, int);