Splitting a string to remove everything after a delimiter

Question

I am trying to parse the phone number out of a sip uri, or if the string is just a number, returning that. Basically, I want to chop off the @ and anything after it if it exists.
I wrote a small function using strtok() but the function always returns NULL.
Can anyone tell me what I'm doing wrong here?

char* GetPhoneNumber(const char* sCallee) {
    char* buf = (char*)malloc(strlen(sCallee) + 1);
    strcpy(buf, sCallee);
    char *p = strtok (buf, "@");
    char *q = strtok (p, ":");
    if (buf) {
        free(buf);
    }
    return q;
}

int main() {
    const char* raw_uri = "2109999999@10.0.0.1";
    char* number = GetPhoneNumber(raw_uri);
    if (number == NULL) {
        printf("I am screwed! %s comes out null!", raw_uri);
    }
    char* second = GetPhoneNumber("2109999999");
    if (second == NULL) {
        printf("This does not work either.");
    }
}

Pablo · Accepted Answer

edit

This

If it's returning NULL because the while loops ends when q is NULL. So I assume that the q = strtok (NULL, ":"); also returns NULL and that's why it leaves the loop.

makes no sense anymore, since you've edited your question and removed the code in question.

end edit

Regardless, you are using it wrong, though.

strtok returns a pointer to the original string plus an offset that marks the beginning of the next token. The pointer is at an offset of buf. So when you do free(buf), you are making the pointers returned by strtok also invalid.

You should also check first if malloc returns NULL and then try to parse it. Checking of malloc returning NULL after the parsing is wrong. Also you would need to make a copy of the value you are returning.

char* GetPhoneNumber(const char* sCallee) {
    char* buf = malloc(strlen(sCallee) + 1);
    if(buf == NULL)
        return NULL;

    strcpy(buf, sCallee);

    char *p = strtok (buf, "@");
    if(p == NULL)
    {
        // no token found
        free(buf);
        return NULL;
    }

    char *q = strtok (p, ":"); // makes no sense after your edit
                               // I don't see any colons in your input
                               // but I leave this to show you how
                               // it would be done if colons were present

    if(q == NULL)
    {
        // no token found
        free(buf);
        return NULL;
    }

    char *copy = malloc(strlen(q) + 1);
    if(copy == NULL)
    {
        free(buf);
        return NULL;
    }

    strcpy(copy, q);
    free(buf);

    return copy;
}

Also when you call this function, you have to remember to free the pointer returned by GetPhoneNumber.

edit2

To be honest, I don't see why you even use strtok if the number comes before @. You can use strchr instead:

char* GetPhoneNumber(const char* sCallee) {

    if(sCallee == NULL)
        return NULL;

    char *p = strchr(sCallee, '@');

    if(p == NULL)
        return NULL; // wrong format

    char *q = calloc(1, p - sCallee + 1);

    if(q == NULL)
        return NULL;

    strncpy(q, sCallee, p - sCallee);

    // q already \0-terminated because of calloc

    return q;
}

Splitting a string to remove everything after a delimiter

Answers (2)

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