Trim

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

char * trim(const char *str)
{
  if(str == NULL)
    return NULL;

  // Trim leading space
  while(isspace(*str)) str++;

  if(*str == 0)  // If string is "empty" - contains only whitespaces -- return null
  {
    return NULL;
  }

  // Trim trailing space
  const char * end = str + strlen(str) - 1; // go to end of string
  while(end > str && isspace(*end)) end--; // go to first nonspace char
  end;

  // Set output size to minimum of trimmed string length and buffer size minus 1
  size_t out_size = (end - str) + 1; // Do not forget to 0
  char *out = malloc(out_size * sizeof(char));

  // Copy trimmed string and add null terminator
  memcpy(out, str, out_size);
  out[out_size] = 0;

  return out;
}


int main(void)
{
    const char * str = "   \t\t   AHOJ SVET \t\t     ";
    printf("String without trim: \"%s\"\n", str);
    char *trimmed = trim(str);
    printf("Trimmed string: \"%s\"\n", trimmed);
    free(trimmed);

    return 0;
}