A simple way to customize macros in C + + _c language

You can use a macro to define a function that has no return value. For example:

Copy Code code as follows:

#define PRINTMAX (A, b) \ do \ {\ int x = A, y = b; \ printf ("Max:%d\n", x > y x:y); \} while (0)// ... Printmax (3, 4);

Such "functions" are essentially different from functions in real sense, because a macro is a compile-time behavior that replaces text only before it is compiled. In the Python source code, you can often see a macro definition similar to the following:

 #define FOO (x) \ Do {\  ... \} while (0) 

Why use the syntax such as do {...} while (0) without directly using {}? By defining the above macro, we can use code like this in the Code: Foo (3); Note the semicolon at the end, which looks like a function, and implements it to represent a statement.  If you use {} instead of Do {...} while (0), it is obviously a grammatical error to use a semicolon.

When working with macros, there are a few things to pay special attention to:

Pay special attention to spaces. The following two macros are the same:

 #define FOO (x) (x << 2) #define BOO (x) (x << 2)//Note the spaces preceding the brackets 

Using a macro to alias a type is a big difference from a typedef. For example:

Copy Code code as follows:

#define INT int * int p1, p2; P1 is a pointer, p2 is an int variable typedef int * INT; INT P1, p2; P1, p2 are pointers//---------------------------------------------------#define LONG long unsigned long v1; V1 is an unsigned long variable typedef long long; unsigned LONG v1; Wrong Oh ~ ~ ~