为什么不能打印出宏创建的结构的所有成员名称？

Question

I'm a bit of a noob when it comes to using macros, but I am running into a problem that I can't explain.

I have used macros to generate the BlockA struct like this:

#define TO_STRUCT(structname, type, member, size) type member size;
#define MEMBER_COUNT(structname, type, member, size) +1
#define MEMBER_NAME(structname, type, member, size)  #member,

#define BLOCK_STRUCT_MEMBERS(p)\
    p(BlockA, RegTypeA, regA, [5])\
    p(BlockA, RegTypeB, regB, )\

 struct BlockA {
    BLOCK_STRUCT_MEMBERS(TO_STRUCT)
    int addr;
    BlockA(int address);
};

And then, I have printed out the count of how many members were put into the struct using the macros:

std::cout << BLOCK_STRUCT_MEMBERS(MEMBER_COUNT);

This prints out the correct response: 2, and if I did the same with the second member commented out when I define it in BLOCK_STRUCT_MEMBERS, it prints 1, which makes sense. So that seems to be working. But if I try to print the names of the members using almost exactly the same method, like this, it only prints the name of the first member:

std::cout << BLOCK_STRUCT_MEMBERS(MEMBER_NAME)

It also complains that it expected an expression when I try to put a semicolon after it, like I did when I printed the count. Why is this happening?

Answer 1

I think it's the comma after "#member" in your "MEMBER_NAME" macro. If I delete it it works fine for me.