C语言去掉字符串末尾的空白字符

#include 
#include 
#include 

//去除尾部空白字符 包括t n r  

char *rtrim(char *str)
{
    if (str == NULL || *str == '')
        {
              return str;
        }

    int len = strlen(str);
    char *p = str + len - 1;
    while (p >= str  && isspace(*p))
    {
         *p = '';
         --p;
     }
        return str;
 }

int main(){
                char dbsname[] = "abc1 23               ";
                char *c;
                int m ;
                for ( m=0; m<20 ;m++){
                        c=&dbsname[m];
                        printf("%c,%d-------n",*c,*c);
                }
        printf("%s",dbsname);
        char *p = rtrim(dbsname);
        printf("%sn",p);
                for ( m=0; m<20 ;m++){
                        printf("%c,%d-------n",*p,*p);
                        p++;
                }

}