string code

/*-----------main.c-----------*/
#include <stdio.h>
#include "text.h"
#include "mem.h"

int main (int argc, char** argv){
    char* string = NULL;

    string = mem_alloc (BUFFER * sizeof (char));
    fgets (string, BUFFER, stdin);
    if (string [strlen (string) - 1] == '\n')
      string [strlen (string) - 1] = '\0';
    printf ("The string is: %s\n", string);
    string = invert_string (string);
    printf ("The inverted string is: %s\n", string);
    free (string);
    return 0;
}

/*-----------text.c-----------*/
#include <stdio.h>
#include "text.h"
#include "mem.h"

/*****Invert String*****/
char* invert_string (char* string){
  char *tmp_str = NULL;
  short int len = 0, i = 0;

  len = strlen (string);
  tmp_str = mem_alloc (BUFFER * sizeof (char));

  for (i = len; i >= 0; i--)
    tmp_str [len - i] = string [i - 1];

  tmp_str [len + 1] = '\0';
  string = tmp_str;
  //free (tmp_str);
  return tmp_str;
}

/*-----------text.h-----------*/
#pragma once

#include <string.h>

#define BUFFER 256

char* invert_string (char* string);

/*-----------mem.c-----------*/
#include "mem.h"

/*****Memory Control*****/
int mem_error = MEM_ERROR_OK;

void* mem_alloc (const size_t size){
    void* result;
    if ((result = malloc(size)) == NULL){
        mem_error = MEM_ERROR_NO_MEMORY;
    }
    return result;
}

int mem_get_error(void){
    return mem_error;
}

int mem_clear_error(void){
    return mem_error = MEM_ERROR_OK;
}

/*-----------mem.h-----------*/
#pragma once

#include <stdlib.h>

#define MEM_ERROR_OK             0
#define MEM_ERROR_NO_MEMORY     -1

void* mem_alloc(const size_t size);

int   mem_get_error(void);
int   mem_clear_error(void);