c - Why does my string comparison fail?

Question

Let's say I have the following code and output:

for (j = 0; j <= i; j++) 
    printf("substring %d is %s
", j, sub_str[j]);

Output:

substring 0 is max_n=20
substring 1 is max_m=20

Now I only want to print some substrings. However, if I try to do this conditionally:

for (j=0; j <=i; j++) {
   if (sub_str[j] == "max_n=20") {
      printf("substring %d is %s
", j, sub_str[j]);
   }
}

I get no output at all. What's wrong with my code?

Answer 1

You can't use == to compare strings in C. You must use strcmp.

for (j=0; j<=i; j++) { 
   if (strcmp(sub_str[j], "max_n=20") == 0) { 
      printf("substring %d is %s
", j, sub_str[j]); 
   } 
}