在整数加法中测试溢出 [英] Test for overflow in integer addition

问题描述

可能重复：

在C / C ++中检测整数溢出的最佳方法

我试图实现简单的程序，测试是否在整数加法期间发生溢出：

  #include< climits> 
 #include< iostream> 
 #include< string> 
 
 using namespace std; 
 
 string overflow（long a，long b）{
 return（（a + b）> UINT_MAX）？true：false 
} 
 
 int main（）{
 long a，b; 
 cout<< enter a and b：; 
 cin>> a>> b; 
 string m = overflow（a，b）; 
 cout<< m; 
 
 return 0; 
} 
  

UINT_MAX = 65535 所以我输入了65535和20，但它写为false为什么？

解决方案 ，此表达式永远不能评估为 true ：

 （a + b）> UINT_MAX 
  

它不能成为 true 是因为 UINT_MAX 是max，所以任何结果（a + b）都不能大于 UINT_MAX ，因为这将是一个矛盾。

您尝试使用更大的数据类型 long 来解决这个问题，但这实际上不能保证大于C ++中的 int 。您可能希望尝试 long long （虽然此类型在标准C ++中不存在）。

说，Java，C ++实际上没有指定每个数据类型必须是多大，所以声明 UINT_MAX = 65535 不是通用的。这只适用于无符号整数以16位保存的处理器。对于32位， UINT_MAX 是 4294967295 。

相关问题

• 在C / C ++中检测整数溢出的最佳方法

另请参阅

• Wikipedia / Limits.h


• cplusplus.com/reference/library/climits

Possible Duplicate:
Best way to detect integer overflow in C/C++

i have tried to implement simple program which tests if overflow occurs during integer addition:

#include <climits>
#include <iostream>
#include <string>

using namespace std;

string overflow(long a,long b){
    return ((a+b)>UINT_MAX)?"true":"false";
}

int main(){
    long a, b;
    cout << "enter a and b: ";
    cin >> a >> b;
    string m = overflow(a,b);
    cout << m;

    return 0;
}

UINT_MAX=65535 so i have entered 65535 and 20 but it wrote false why?

解决方案

Given unsigned int a, b, this expression can never evaluate to true:

(a+b) > UINT_MAX

The reason why it can't ever be true is because UINT_MAX is the max, so whatever result (a+b) is can never be greater than UINT_MAX, because that would be a contradiction.

You tried to use a bigger data type long to get around this, but this is actually not guaranteed to be bigger than int in C++. You may want to try long long instead (although this type does not exist in standard C++).

Unlike, say, Java, C++ does not actually specify how large each data type must be, so the claim that UINT_MAX=65535 is not universally true. It's only true for processors where an unsigned integer is held in 16 bits. For 32 bits, UINT_MAX is 4294967295.

Related questions

• Best way to detect integer overflow in C/C++

See also

• Wikipedia/Limits.h
• cplusplus.com/reference/library/climits

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