Pride and revulsion

Here's a bug that bit me recently. I wrote a very small quick and dirty TDD header for C in my CyberDojo. It has a macro called CHECK_EQ which you use as follows:

CHECK_EQ(int, 42, 9*6);

Part of the macro looks like this:

#define CHECK_EQ(type, expected, actual) \
    ... \
    type e = expected; \
    type a = actual; \
    ... \

Can you see the problem? Well, suppose it's used like this:

    int e = 42;
    CHECK_EQ(int, e, 9*6);

Can you see it now? The problem is that this line in the macro

    type e = expected; \

gets expanded into this line:

    type e = e; \

Ooops. I thought about choosing a very cryptic name instead of x. Perhaps incorporating __LINE__ as a suffix. But I felt there had to be a solution that would always work. After some thought I came up with this. Brace yourself...

#define CHECK_EQ(type, expected, actual) \
   ...
   if (#expected[0] != 'x') \
   { \
       type x0 = expected; \
       type x1 = actual; \
       ... \
   } \
   else \
   { \
       type y0 = expected; \
       type y1 = actual; \
       ... \
   } \
   ...

Like Tom Duff, I feel a mixture of pride and revulsion at this discovery.