Program in C to compare strings. The strings will be equal if there are white spaces in the tail.

strcmpws.c

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

int strcmpws(const char *s1, const char *s2)
{
  char *r1 = strdup(s1);
  char *r2 = strdup(s2);
  int f = 0;
  
  if (r1 != NULL)
  {
    char *fr1 = r1 + strlen(s1) - 1;
    while( (isspace(*fr1) || !isprint(*fr1) || *fr1 == 0) && fr1 >= r1) --fr1;
    *++fr1 = 0;
  }
  
  if (r2 != NULL)
  {
    char *fr2 = r2 + strlen(s2) - 1;
    while( (isspace(*fr2) || !isprint(*fr2) || *fr2 == 0) && fr2 >= r2) --fr2;
    *++fr2 = 0;
  }

  for(int i=0; r1[i]!='\0'; i++)
  {
      if(r1[i] == r2[i]) f = 0; else f = -1;
  }
  //if (strcmp(r1, r2) == 0) f = 0; else f = -1;
  free(r1);
  free(r2);
  
  return f;
}

const char *a = "     this is a string      ";
const char *b = "     this is a string";
 
int main()
{
  printf("'%d'\n'", strcmpws(a,b));

  return 0;
}