Question

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What does ## mean for the C(C++) preprocessor?

#define SIMPLE16_DESC_FUNC1(num1, log1) \
    bool                            \
    Simple16::try##num1##_##log1##bit(uint32_t *n, uint32_t len)    \
    {                                       \
            uint32_t        i;              \
            uint32_t        min;            \
\
            min = (len < num1)? len : num1; \
\
            for (i = 0; i < min; i++) {     \
                    if (int_utils::get_msb(n[i]) > log1 - 1)        \
                            return false;   \
            }               \
\
                return true;    \
        }

I found this code in someone’s code, it seems “##” operator plays an important role in the function name. Anyone tells me what its usage?

Answer 1

It’s the token pasting operator. It concatenates two tokens where one is an argument to the macro.