Can a C macro contain temporary variables?

Question

I have a function that I need to macro\'ize. The function contains temp variables and I can\'t remember if there are any rules about use of temporary variables in macro subs

Answer 1

This is mostly OK, except that macros are usually enclosed with do { ... } while(0) (take a look at this question for explanations):

#define ALLOC_FOO(f, size) \
    do { \
        long      i1, i2;\
        double   *data[7];\
        /* do something */ \
    } while(0)

Also, as far as your original fooAlloc function returns long you have to change your macro to store the result somehow else. Or, if you use GCC, you can try compound statement extension:

#define ALLOC_FOO(f, size) \
    ({ \
        long      i1, i2;\
        double   *data[7];\
        /* do something */ \
        result; \
    })

Finally you should care of possible side effects of expanding macro argument. The usual pattern is defining a temporary variable for each argument inside a block and using them instead:

#define ALLOC_FOO(f, size) \
    ({ \
        typeof(f) _f = (f);\
        typeof(size) _size = (size);\
        long      i1, i2;\
        double   *data[7];\
        /* do something */ \
        result; \
    })