Use of # # in C + + (GO)

Transferred from: http://blog.sina.com.cn/s/blog_4cf015f201009o1d.html

The first case is a stringizing Operator (#), called a string.

#define Stringer (x) printf (#x "\ n") int main () {     stringer (in quotes in the printf function call\n);     Stringer ("in quotes when printed to the screen" \ n);     Stringer ("this: \" Prints an escaped double quote "); }

Such a definition will be converted to the following code when it is processed:

int main () {     printf ("in quotes in the printf function call\n" \ n ");     printf ("\" in quotes-printed to the screen\ "\ n" "\ n");     printf ("\" this: \\\ "prints an escaped double quote\" "\ n"); }

The results of the program run as follows:

In quotes in the printf function call ' in quotes when printed to the screen ' this: \ ' Prints an escaped double quotation m Ark

The second situation as charizing Operator (#@), is called the word Fu Hua.

Example:

#define MAKECHAR (x) #@x

Causes the statement

A = Makechar (b);

This statement will be extended to

A = ' B '; Note that single quote characters cannot be used with such a character.

The third situation as token-pasting Opertor (# #), called the connector, is probably the meaning.

Example: #define PASTER (N) printf ("token" #n "=%d", token# #n) int token9 = 9;

If a number is called as a parameter to this macro,

Paster (9);

The macro is expanded to

printf ("token" "9" "=%d", token9);

Then it becomes the statement: printf ("Token9 =%d", token9);

Use of # # in C + + (GO)