Question

I had tried to do it myself but failed (I am tempted to do it again for learning but just need it for an example program). Essentially I wish to represent a binary number but padded of course to the nearest byte with 0‘s so I found a function on another question here:

char * string_pad(char * string, size_t padlen, char * pad) {
    size_t lenstring = strlen(string);
    size_t lenpad = strlen(pad);

    char * padded = (char*)malloc(lenstring + lenpad + 1);
    strncpy(padded, string, lenstring); /* copy without '\0' */
    padded += lenstring; /* prepare for first append of pad */
    for(padlen += 1; padlen > 0; padlen--, padded += lenpad)
        strncpy(padded, pad, lenpad);
    *padded = '\0';
    return padded;
}

I am calling it like this:

printf("Test: %s\n", string_pad(dec2bin(~myInt), 32, "0"));

Unfortunately it prints “Test: ” but nothing else. My dec2bin returns a simple char pointer by the way if you need to know.

What seems to be causing it to do nothing?

Why does this function accept char* pad and not char pad so I can do just pad it with ‘0’, will “0” work too or does it add a null terminator screwing it up or something?

EDIT: Or can somebody provide a simple example (or what I need to do what) to pad left for this? This snippet does not appear to be all that good..

I was thinking of creating a chararray initialized to zero, then copying the binary after that, but how to make it work escaped me..

Answer 1

“padded” points to the end of the string when you are returning it.