Why printf prints same string when function called back to back inside same statement

user9lG5 0
Viewed 47

In the below snippet, printf( ) prints same string even though the char array has been memset to 0.

#include <stdio.h>
#include <string.h>

char ip_addr[20];
char *ip_print(char *in)
{
    memset(ip_addr,0,20);
    strcpy(ip_addr,in);
    return ip_addr;
}
int main()
{
    printf("Ip addresses %s - %s",ip_print("226.0.0.1"),ip_print("10.1.1.1"));
    return 0;
}

output- Ip addresses 226.0.0.1 - 226.0.0.1

Expected output- Ip addresses 226.0.0.1 - 10.1.1.1

printf function arrays c
1 Answers

As @Pablo said above ip_print() updates a global variable and returns the (same) address twice. The order of evaluation of arguments, however, is unspecified so the result is undefined behavior (it may print either address twice).

Allan Wind0
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