Is it possible to un-const typeof in gcc pure C?

Question

I have a macro that uses GCC\'s typeof to create a variable of the same type of a macro argument. The problem is: if that argument has const type, the variable crea

Answer 1

You could use a C11 _Generic selection to map from const to non-const type:

#define DECR_(t, x) ({ t y = (x); --y; y; })
#define DECR(x) _Generic((x),                     \
    int: DECR_(int, (x)),                         \
    const int: DECR_(int, (x)),                   \
    long: DECR_(long, (x)),                       \
    const long: DECR_(long, (x)),                 \
    unsigned int: DECR_(unsigned int, (x)),       \
    const unsigned int: DECR_(unsigned int, (x)), \
    long long: DECR_(long long, (x)),             \
    const long long: DECR_(long long, (x)))

Although it involves a LOT of typing, even if you only need to cover integral types. C11 is also far from being widely available these days. Live example at Coliru.