Daily WTF

Whenever I’m writing C code I am amazed that we have to keep track of things like array lengths and string terminators. It’s no wonder poor coders create weird bugs, like this one I found in my work code for storing atom names (like chlorine-1, carbon-2, etc).

char names[MAX_NAMES][6];
int num_names, i;
for(i=0; i < num_names; i++) {
    printf("(%d) %s\n", i, names[i]);
}

This is what I see:

(0)  CL1   CL2   C2 
(1)  CL2   C2 
(2)  C2 
(3)  CD2   N2 
(4)  N2 
...

WTF? Turns out there are exactly three spaces around each of those strings, making the 3-character names overflow. That’s what happens when you use strcpy on strings that are too short to contain the result.