PSET6 - Why is my filename string getting weird characters after two refreshes?

Question

This is my code to extract the filename requested from the server from the request message:

char* buffer2 = strchr(buffer1, '/');
char* buffer3 = strchr(buffer2, ' ');

char* buffer4 = malloc(strlen(buffer2) - strlen(buffer3));
if (!buffer4)
{
    error(500);
    return false;
}
strncpy(buffer4, buffer2, (strlen(buffer2) - strlen(buffer3)));

Later on, buffer4 is copied to abs_path.

This code works perfectly the first or second time the image is requested, but after that buffer4 becomes things like " /cat.jpgjpg�]r" instead of just "/cat.jpg".

I always free buffer4 later after copying it to abs_path. Any suggestions on why this is happening? many thanks in advance

Answer 1

While this may not be the only problem, the math is "backwards". Remember, buffer3 is greater than buffer2 (found later in the string). So, buffer2 - buffer3 would not be the result you are after. Also, make sure to allocate enough memory for the null terminator. The reason it works sometimes: memory is fickle. :)