Trim strings in C

trim.c

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

int is_ws(char c) {
  return c == ' ';
}

int trim(const char* src, char** dst) {
  if (strlen(src) == 0)
    return 0;

  size_t src_size = strlen(src);

  int lp /* left padding */ = 0;
  int rp /* right padding */ = 0;
  while (is_ws(src[lp]) && ++lp);;
  while (is_ws(src[src_size-rp-1]) && ++rp);;

  /* optionally reallocate to not waste unused memory */
  /* NOTE: change this to malloc if you don't want to pre-allocate the out buffer */
  if (lp+rp != 0)
    (*dst) = (char*)realloc((*dst), sizeof(char) * src_size-lp-rp);

  int i;
  for (i = lp; i < src_size-rp; ++i)
    (*dst)[i-lp] = src[i];

  (*dst)[src_size-lp-rp] = '\0';
  return lp+rp;
}


int main(int argc, char** argv) {
  if (argc < 2) { printf("usage: trim string\n"); return 1; }
  char *bar = malloc(sizeof(char) * strlen(argv[1]));
  trim(argv[1], &bar);
  printf("Source string:\t'%s'\nTrimmed string:\t'%s'\n", argv[1], bar);
  free(bar);
}