C++/C macro definition (define) the Meaning of # # # in macro concatenation __c++

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C++/C macro definition (define) the Meaning of # # #

The # # # in define is commonly used for stitching strings, but in the actual use of the process, there are some subtle differences, we have a few examples to see.

#是字符串化的意思, the # that appears in the macro definition is to turn the arguments that follow in to a string;

eg

#define STRCPY__ (DST, SRC) strcpy (DST, #src)

Strcpy__ (BUFF,ABC) is equivalent to strcpy__ (buff, "abc")

# #是连接符号, connect the parameters together

#define FUN (ARG) my# #arg

Then FUN (ABC)

Equivalent to MYABC

Let's look at a concrete example.

#include <iostream>

using namespace Std;

#define OUTPUT (a) cout<< #A << ":" << (a) <<endl;

int main () {

int a=1,b=2;

OUTPUT (a);

OUTPUT (b);

OUTPUT (A+B);

return 1; }

Get rid of the # number. We got the result and printed the value of the a,b directly, which is in line with the grammatical rules, so the role of # is obvious. #include <iostream>

using namespace Std;

#define OUTPUT (a) cout<<a<< ":" << (a) <<endl;

int main ()

{

int a=1,b=2;

OUTPUT (a);

OUTPUT (b);

OUTPUT (A+B);

return 1;

}