Problem with char returning strange characters

Question

The intention is to replace all words toda for 0, however after X characters it starts returning strange values as can be observed in the comments.

I think I’m handling the parameters wrong, but at what point? Why?

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

/*
 * @brief
 * PHP's str_replace ported to C
 * @author Silver Moon ([email protected])
 * 
 */

char *str_replace(char *search , char *replace , char *subject)
{
    char  *p = NULL , *old = NULL , *new_subject = NULL ;
    int c = 0 , search_size;

    search_size = strlen(search);

    //Count how many occurences
    for(p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search))
    {
        c++;
    }

    //Final size
    c = ( strlen(replace) - search_size )*c + strlen(subject);

    //New subject with new size
    new_subject = malloc( c );

    //Set it to blank
    strcpy(new_subject , "");

    //The start position
    old = subject;

    for(p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search))
    {
        //move ahead and copy some text from original subject , from a certain position
        strncpy(new_subject + strlen(new_subject) , old , p - old);

        //move ahead and copy the replacement text
        strcpy(new_subject + strlen(new_subject) , replace);

        //The new start position after this search match
        old = p + search_size;
    }

    //Copy the part after the last search match
    strcpy(new_subject + strlen(new_subject) , old);

    return new_subject;
}


char* change(char *original) {
    char end[100];

    strcpy(end, str_replace("toda",        "0", original));

    return end;
}

int main()
{
    char *original[100],
         *final[100];

    printf("digite:");

    fgets(original, sizeof(original), stdin); // obtem valor -> toda toda toda toda toda toda toda toda

    strcpy(final, change(original)); // salva em final o valor alterado
    printf("[%s]", final); // retorna: [0 \336\3770 0 0 0 0 \220\360\277_\377]

    return 0;
}

Answer 1

There was no reason to use pointer there in the declaration of the initial variables. If you were to use pointer you should not use array, then would allocate with malloc() which by the way is used of the function of replace and was wrong for not having his include.

In function change() should wear a malloc() to allocate into heap. See the links below to understand better. But in fact this function is not even necessary, It can to simplify. It might even be useful to abstract the operation, but I see no gain in this case. I think until the variable final is unnecessary, but I haven’t seen if it has any side effects on str_replace() that creates some complication.

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

char *str_replace(char *search , char *replace , char *subject) {
    char  *p = NULL , *old = NULL , *new_subject = NULL ;
    int c = 0 , search_size;
    search_size = strlen(search);
    //Count how many occurences
    for (p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search)) {
        c++;
    }
    //Final size
    c = ( strlen(replace) - search_size )*c + strlen(subject);
    //New subject with new size
    new_subject = malloc( c );
    //Set it to blank
    strcpy(new_subject , "");
    //The start position
    old = subject;
    for (p = strstr(subject , search) ; p != NULL ; p = strstr(p + search_size , search)) {
        //move ahead and copy some text from original subject , from a certain position
        strncpy(new_subject + strlen(new_subject) , old , p - old);
        //move ahead and copy the replacement text
        strcpy(new_subject + strlen(new_subject) , replace);
        //The new start position after this search match
        old = p + search_size;
    }
    //Copy the part after the last search match
    strcpy(new_subject + strlen(new_subject) , old);
    return new_subject;
}

int main() {
    char original[100], final[100];
    printf("digite:");
    fgets(original, sizeof(original), stdin);
    strcpy(final, str_replace("toda", "0", original));
    printf("[%s]", final);
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

If you’re really gonna use change(), which is a waste:

char* change(char *original) {
    char *end = malloc(100);
    strcpy(end, str_replace("toda", "0", original));
    return end;
}

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