strcmp says seemingly identical string are not equal

Question

I am using strcmp to compare two strings. lhs is coming from a filestream via fgets. rhs is being created generated by a for loop to be a sequence of n-1 whitespaces.

---

Example

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

int main() {
  size_t n = 10;
  char rhs[n];

  memset(rhs, ' ', n - 1); // Fill with spaces using memset()
  rhs[n-1] = 0; // Add NUL terminator

  printf("len=%zu\n", strlen(rhs));

  char lhs[n];

  FILE* file = fopen("test", "r");
  fgets(lhs, sizeof(lhs), file);
  printf("read=%s\n", lhs);

  return 0;
}

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When using gdb, I will find that I have two strings that appear identical (I used gdb's print for this):

lhs = " "

rhs = " "

Yet, strcmp(lhs, rhs) != 0. This should return a 0 indicating that the strings are identical, but instead I get some other non-zero value.

Why aren't these strings considered equal?

Answer 1

Cleaned up this code to create a complete, minimal example looks like this:

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

int main() {
  size_t n = 10;
  char rhs[n];

  memset(rhs, ' ', n - 1); // Fill with spaces using memset()
  rhs[n-1] = 0; // Add NUL terminator

  printf("len=%zu\n", strlen(rhs));

  char lhs[n];

  FILE* file = fopen("test", "r");
  fgets(lhs, sizeof(lhs), file);
  printf("read=%s\n", lhs);

  return 0;
}

Where here it's important to not assign from fgets, that's a warning if you have -Wall turned on.