C Pre-processor

1. #define

Using parameters in define

Note: The preprocessor does not perform calculations, only string substitution

Output

Here's the x+2, replaced and changed to X+2*X+2=14

Here the 100/square (2) is replaced and then becomes 100/2*2=100

++x*++x here the compiler multiplies x by two times

2. #运算符和 # #运算符

From the previous example, you can see that the macro in double quotes is not working, but how to include the macro parameter (#) in the string, this process is called string;

and # like, # #运算符可以用于类函数宏的替换部分

E.

Res:

3. Variable Macros: ... And _ _va_args_ _

Res:

3. #undef

Function: Cancels the definition of a given # define

#define LIMIT 400

#undef LIMIT

4. Conditional compilation

#ifdef/#ifndef #else (On Demand) #endif (must exist)

1#include <stdio.h>2 #defineJust_checking3 #defineLIMIT 44 5 intMain ()6 {7    inti;8    intTotal ;9 Ten    for(intI=1; i<=limit;i++) One   { Atotal+=2*i*i+1; - #ifdef just_checking -printf"i=%d,running total =%d \ n", total); the    #endif -    } -printf"Grand total =%d \ n", total); -    return 0; +}

5. #line and #error

#line 1000/* Current line number is 1000*/

#line "COOL.C"

6. #pragma--compiling instructions

C Pre-processor