c preprocessor - What's the meaning of ## in the define code in C++ -

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• how concatenate twice c preprocessor , expand macro in “arg ## _ ## macro”? 2 answers

#define declare_delete_ptr(type) \ void deleteptr_##type(string &operand) \ {\ }\ 

what's meaning of ## in macro definition in c++?

what's difference followed code?

#define make_strings(var) #var 

it 1 #, former 2 #

it concatenates value pass through parameter type...

declare_delete_ptr(gremlin) 

would expand to:

void deleteptr_gremlin(string &operand) { }