[cpp]: 好玩的“宏定义(macro)”

[cpp]:  好玩的“宏定义(macro)”

 

 

 

 

一、有趣的“宏定义”

 

　　1、思想/原理：用【宏macro】，定义【伪指令directive】。

 

　　2、命令格式：　　#define 　　[directive_name]　　[function or ...]

 

　　3、应用实例：

// directive entry
#define __main_begin    int main(int argc, char * argv[], char *envp[]){     // entry first part
#define __main_end      ; return 0; }   // entry second part

 

 

 

 

二、源程序

#include <iostream>


// directive counter
int icount = 0;


// directive entry
#define __main_begin        int main(int argc, char * argv[], char *envp[]){     // entry first part
#define __main_end      ; return 0; }   // entry second part


// initialize value of 'icount'; or reset value of 'icount';
#define __big_begin     big_begin();
#define __big_end       big_end();


// directives to be ran
#define __cmd       big();


// function big
void big()
{
    icount++;
    std::cout << "\t[os] big(" << icount << ")" << std::endl;
}


// initial directive counter
void big_begin()
{
    icount = 0;
    std::cout << "[os] big_begin::set_icount := " <<  icount << std::endl;
}


// resetting directive counter
void big_end()
{
    icount = 0;
    std::cout << "[os] big_end::set_icount := " <<  icount << std::endl;
}


// old entry of the program
/*
int main()
{
    __cmd
    __cmd

}
*/


__main_begin

    __big_begin
    
        __cmd
        __cmd
        __cmd
        
    __big_end
    
__main_end

 

 

 

 

三、运行结果

g++ -std=c++20 -O2 -Wall -pedantic -pthread main.cpp && ./a.out


[os] big_begin::set_icount := 0
    [os] big(1)
    [os] big(2)
    [os] big(3)
[os] big_end::set_icount := 0

 

 

 

 

四、参考资料

 

　　1、无