005 ++i和i++原理

 

/*
目录:
   一 代码测试
   二 汇编原理
   三 仿写函数
*/

 

一 代码测试

int main()
{

    int i = 3;
    int k = 0;
    int m = 0;

    k = ++i;
    printf("k = %d i = %d\n", k, i);

    m = i++;
    printf("m = %d i = %d", m, i);

    return 0;
}

/*
// result
k = 4 i = 4
m = 4 i = 5
*/

 

二 汇编原理

    k = ++i;
00044E63  mov         eax,dword ptr [i]  
00044E66  add         eax,1  
00044E69  mov         dword ptr [i],eax  
00044E6C  mov         ecx,dword ptr [i]  
00044E6F  mov         dword ptr [k],ecx  

    m = i++;
00044E87  mov         eax,dword ptr [i]  
00044E8A  mov         dword ptr [m],eax  
00044E8D  mov         ecx,dword ptr [i]  
00044E90  add         ecx,1  
00044E93  mov         dword ptr [i],ecx  

 

三 仿写函数

#include "stdafx.h"


int FirstPlus(int *pInt)
{
    *pInt = *pInt + 1;
    return *pInt;
}

int AfterPlus(int *pInt)
{
    int nReturn = 0;

    nReturn = *pInt;
    *pInt = *pInt + 1;

    return nReturn;
}


int main()
{
    int i = 3;
    int k = 0;
    int m = 0;

    printf("k = %d i = %d\n", k, i);
    k = FirstPlus(&i);
    printf("k = %d i = %d\n\n", k, i);

    printf("m = %d i = %d\n", m, i);
    m = AfterPlus(&i);
    printf("m = %d i = %d", m, i);

    return 0;
}

/*
// result
k = 0 i = 3
k = 4 i = 4

m = 0 i = 4
m = 4 i = 5
*/