trim the blank in the head or in the tail

trim.c

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

//erase the blank int the tail 
char *rtrim(char *str)
{
    if(NULL == str || *str == '\0')
    {
        return str;
    }
    int len = strlen(str);
    char *p = str + len - 1;
    while( p >= str && isspace(*p))
    {
        *p = '\0';
        --p;
     }
     
     return str;
 }
 
 //erase the blank in the head
 char *ltrim(char *str)
 {
    if( NULL == str || *str == '\0')
    {
        return str;
    }
    
    int len = 0;
    char *p = str;
    while(*p != '\0' && isspace(*p))
    {
      ++p;
      ++len;
     }
     
     memmove(str,p, strlen(str) - len + 1);
     
     return str;
}

char* trim(char *str)
{
   str = rtrim(str);
   str = ltrim(str);
   
   return str;
   }
   
 void demo()
 {
      char str[] = "  ab  c ";
      printf("before trim:%s\n", str);
      
      char *p = trim(str);
      printf("after trim:%s\n", p);
 }
 
 int main(int argc, char **argv)
 {
    demo();
    
    return 0;
  }