Integer not comparing equal to its value

Question

I've got a piece of code I am trying to debug, which is producing bizarre results. An integer, which very clearly contains the value six, compares false to the literal 6.
In my code, this code:

int allGreen = 0;
int index = 0;
while (ch->fb[index]->selection_color() == FL_GREEN) 
{
    ++allGreen;
    ++index;
}
std::cout << allGreen << std::endl;
std::cout << std::boolalpha << (allGreen == 6) << std::endl;

Produces the output:

6
false

I am compiling with g++ 4.8.2 on Ubuntu.

How can this possibly happen?

Edit: Removing all green from the condition doesn't help. Edit 2: index and allGreen are equal, as expected. Neither is equal to 6, despite both being 6.

Answer 1

What is the size of ch->fb array? If it is 6 or less, it could be compiler optimizing undefined behavior here.

When seeing some simple loop like

while ( a[i] ) i++;

Compiler can make an assumption that i never goes outside of a array, otherwise program invokes undefined behavior. That is i lies between 0 and size of a - 1.

Later, if compiler sees something like i == 8, there 8 is larger than size of a - 1, it replaces this condition with false.

Just to be sure, you can look at assembly code.