C++ Macros: manipulating a parameter (specific example)

问题

I need to replace

GET("any_name")

with

String str_any_name = getFunction("any_name");

The hard part is how to trim off the quote marks. Possible? Any ideas?

回答1:

How about:

#define UNSAFE_GET(X) String str_##X = getFunction(#X);

Or, to safe guard against nested macro issues:

#define STRINGIFY2(x) #x
#define STRINGIFY(x) STRINGIFY2(x)
#define PASTE2(a, b) a##b
#define PASTE(a, b) PASTE2(a, b)

#define SAFE_GET(X) String PASTE(str_, X) = getFunction(STRINGIFY(X));

Usage:

SAFE_GET(foo)

And this is what is compiled:

String str_foo = getFunction("foo");

Key points:

Use ## to combine macro parameters into a single token (token => variable name, etc)
And # to stringify a macro parameter (very useful when doing "reflection" in C/C++)
Use a prefix for your macros, since they are all in the same "namespace" and you don't want collisions with any other code. (I chose MLV based on your user name)
The wrapper macros help if you nest macros, i.e. call MLV_GET from another macro with other merged/stringized parameters (as per the comment below, thanks!).

回答2:

One approach is not to quote the name when you call the macro:

#include <stdio.h>

#define GET( name ) \
    int int##name = getFunction( #name );   \


int getFunction( char * name ) {
    printf( "name is %s\n", name );
    return 42;
}

int main() {
    GET( foobar );
}

回答3:

In answer to your question, no, you can't "strip off" the quotes in C++. But as other answers demonstrate, you can "add them on." Since you will always be working with a string literal anyway (right?), you should be able to switch to the new method.

来源：https://stackoverflow.com/questions/806543/c-macros-manipulating-a-parameter-specific-example

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c++

c-preprocessor