Generating functions with macros in C++

问题:

I have the following macro that is intended to generate functions in the current scope or namespace:

#define MAKE_FUNC(FNAME) \
template <typename T> \
T ##FNAME## (const T& t) \
{\
   return t; \
}

MAKE_FUNC(foo)
MAKE_FUNC(boo)

int main()
{
   foo(1);
   boo(2);
}

The following is the error message when compiling the above code:

prog.cpp:8:1: error: pasting "Tfoo" and "(" does not give a valid preprocessing token
prog.cpp:9:1: error: pasting "Tboo" and "(" does not give a valid preprocessing token
prog.cpp:8: error: ISO C++ forbids declaration of ‘Tfoo’ with no type
prog.cpp:9: error: ISO C++ forbids declaration of ‘Tboo’ with no type
prog.cpp: In function ‘int main()’:
prog.cpp:13: error: ‘foo’ was not declared in this scope
prog.cpp:14: error: ‘boo’ was not declared in this scope

http://ideone.com/paiu1

It seems like the concatenation has fail, is there anyway around this problem?

回答1:

You want

T FNAME (const T& t) \

## concatenates, you don't want to concatenate.