Retrieve path of symbolic link

I want to store the path of the file the symbolic link is pointing to into bufff. This works with my current implementation using readlink but it grabs extra data I don’t need because my bufsize is arbitrarily valued. I’m not sure how to size it according to the path of what the symbolic link points to because all I have is the path to the symbolic link. This is stored in path which is a char array. How do I know to size bufff with the size of the direct path string of the link if all I have is the path to the symbolic link?

char bufff[100];
size_t bufsize = 100;
readlink(path,bufff,bufsize);

Answer

The readlink() function returns the number of bytes copied to your buffer, without the final . This means that if you call readlink() with a buffer of 100 bytes and readlink() returns 100, you need more space (even if the path was exactly 100 bytes, you would still need at least 1 byte to add a null character at the end).

The solution is to increase your buffer in a loop:

size_t bufsize = 255; /* Initial buffer size */
ssize_t result;
char* buf = malloc(bufsize); /* Initial buffer allocation */
while ((result = readlink(path, buf, bufsize)) >= bufsize) {
    /* We double the buffer size, so next call should succeed ! */
    bufsize *= 2;
    buf = realloc(buf, bufsize);
}
buf[result] = '';

WARNING: This is just an example, we don’t check if readlink returns -1 in case of errors. Same for malloc and realloc. You should check errors in real-world.