[C Language] How to trim a string

#define LTRIM(s) trim(s,1)
#define RTRIM(s) trim(s,2)
#define TRIM(s) trim(s,0)
/* This function remove all white spaces from the right and left
end of a string
INPUT str : string to analize
INPUT mode: possible value ->
0,3: Remove all white spaces from the right and left end of a string
1  : Remove all white spaces from the left string
2  : Remove all white spaces from the right string
RETURN 0 : for empthy string otherwise 1
*/
char trim(char* str,char mode)
{
   char *s,*p;
   char *sp,*ep;
   if (strlen(str)==0)//empty string
      return 0;
   s= malloc(strlen(str));//reserve area
   s=str;// copy string to new area
   p=s;
   if (!mode)
      mode=3;//complete trim
   if (mode & 1)
   {
      while(isspace(*p))//left trim
         p++;
   }
   sp=p;
   if (mode & 2)
   {
    p=p+strlen(p);
    p--;

    while(isspace(*p))//right trim
       p--;
    p++;
    *p=0;//null char to end string
}

   strcpy(str,sp);//update new string

   free(s);//free memory
return 1;
}
void Testfunction()
{
   char strm[50];
   sprintf(strm,"     Hello World     ");

   printf("Start len:%d string <%s> \n",strlen(strm),strm);

   LTRIM(strm);
   printf("Ltrim len:%d string <%s>\n",strlen(strm),strm);
   RTRIM(strm);
   printf("Rtrim len:%d string <%s> \n",strlen(strm),strm);

   sprintf(strm,"     Hello World     ");
   TRIM(strm);
   printf("TRIM len:%d string <%s> \n",strlen(strm),strm);

   return;

}

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