整数相乘容易出错实例

 

///



/* 1、测试 两个 int32 整数相乘，结果放保存在uint64整数，测试输出结果是否正确
 * 2、
 * 3、
 *
 * date: 2018-05-25
 */

#include <iostream>
#include <fstream>
#include <vector>
#include <stdio.h>
#include<stdlib.h>
#include<string>

using uint32 = unsigned int;
using uint64 = unsigned long long int;
using uint8 = unsigned char;


const uint64 K_512 = 512 * 1024;
const uint64 K_1024 = 1024 * 1024;

uint64 MAX_MEM = 3 * 1024 * K_1024;

//uint64 MAX_MEM = 3;

/// first argv: original string
int main(int argc, char** argv)
{

    uint64 value_64 = 0;

    uint32 v1 = 1024 * 1024 * 1024;
    uint32 v2 = 5;
    value_64 = v1 * v2;

    std::cout << "32位整数 * 32位整数 ：\n" ;
    std::cout << " v1 * v2 = " << v1 * v2 << std::endl;
    std::cout << "value_64 = " << value_64 << std::endl;
    std::cout << std::endl;

    uint32 v3 = 1024 * 1024 * 1024;
    uint64 v4 = 5;
    value_64 = v3 * v4;

    std::cout << "32位整数 * 64位整数 ： \n" ;
    std::cout << " v3 * v4 = " << v3 * v4 << std::endl;
    std::cout << "value_64 = " << value_64 << std::endl;
    std::cout << std::endl;

    uint64 v5 = 1024 * 1024 * 1024;
    uint32 v6 = 5;
    value_64 = v5 * v6;

    std::cout << "64位整数 * 32位整数 ： \n" ;
    std::cout << " v5 * v6 = " << v5 * v6 << std::endl;
    std::cout << "value_64 = " << value_64 << std::endl;


}

    结果：

      32位整数 * 32位整数 ：
      v1 * v2 = 1073741824
      value_64 = 1073741824

      32位整数 * 64位整数 ：
       v3 * v4 = 5368709120
      value_64 = 5368709120

      64位整数 * 32位整数 ：
       v5 * v6 = 5368709120
      value_64 = 5368709120