Helping out to fix a C substring generator

substr.c

// The MIT License (MIT)
 
// Copyright (c) 2015 Vanderci Curvelo Jr, Leonardo de Oliveira Lourenço
 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
 
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

/* Original: https://github.com/vandercijr/cplus_strings/blob/master/cplus_strings.c
*/

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

/*
* char *substr(char *str, int start, int length)
* extrai uma substring de uma string
* retorna um ponteiro char para a substring
*
*/
char *substr(char *str, int start, int length)
{
    char *_substr;

    //aloca memoria para a substring (+1 para o \0)
    _substr = (char *) malloc((length + 1) * sizeof(char));

    if(_substr != NULL)
    {
        //copia a substring para a variavel
        strncpy(_substr, str+start, length);
        //finaliza a string com o caracter nulo
        _substr[length] = '\0';
    }

    return _substr;
}

/*
* char **split(char *str, char delimiter)
* transforma uma string em um array baseado em caracteres separadores
* retorna um array char
*
*/
char **split(char *str, char delimiter)
{
    char **tokens;
    char *current;
    char *previous = NULL;
    char separator[2];
    int length;
    int length_substr;
    int separators_found = 0;
    int offset = 0;

    length = (int) strlen(str);

    separator[0] = delimiter;
    separator[1] = '\0';

    //conta as ocorrencias de caracteres separadores
    do
    {
        current = strstr(str+offset, separator);
        if(current != NULL)
        {
            offset = (current - str) + 1;
            separators_found++;
        }
    } while(current != NULL);

    //aloca memoria para a o array de tokens (substrings)
    tokens = (char **) malloc((separators_found+2) * sizeof(char *));

    if(tokens != NULL)
    {
        tokens[separators_found+1] = NULL;
        // tokens[separators_found] = NULL;
        offset = 0;

        for(int i = 0; i < (separators_found+1); ++i)
        {
            //aponta para o caracter encontrado
            current = strstr(str+offset, separator);

            //calcula o tamanho da string que está entre os caracteres de separação
            length_substr = (current != NULL) ? current - ((previous != NULL) ? (previous+1) : str) : (str+length) - (previous-1);

            tokens[i] = substr(str, offset, length_substr);

            offset = (current != NULL) ? (current - str) + 1 : 0;
            previous = current;
        }
    }

    return tokens;
}

void free_tokens(char ***tokens)
{
    for(int i = 0; (*tokens)[i] != NULL; ++i)
    {
        free((*tokens)[i]);
    }

    free(*tokens);
    *tokens = NULL;
}

/*
*
* Teste das funções de string
*
*/
int main(void)
{
    char *msg;
    char **arr;

    msg = "DEVICE 0|W|abcdefghijkl|FFF321";

    arr = split(msg, '|');

    if(arr == NULL)
    {
        printf("Split error!");
        return 1;
    }

    for(int i = 0; arr[i] != NULL; ++i)
    {
        printf("  token: [%s]\n", arr[i]);
    }

    free_tokens(&arr);

    return 0;
}