使用'cin'读取'unsigned int' [英] Reading 'unsigned int' using 'cin'

问题描述

我想使用 cin 读取 unsigned int ，如下所示：

  #include< limits.h> 
 #include< iostream> 
 
 using namespace std; 
 
 int main（int argc，char * argv []）
 {
 unsigned int number; 
 
 // UINT_MAX = 4294967295 
 cout< 请输入介于0和<< UINT_MAX<< ：<< endl 
 
 cin>>数; 
 
 //检查数字是否是有效的无符号整数
 if（（number< 0）||（（unsigned int）number> UINT_MAX））
 {
 cout<< 无效号码。 << endl 
 return -1; 
} 
 return 0; 
} 
  

但是，每当输入大于无符号整数 UINT_MAX ），程序显示 3435973836 。如何检查用户提供的输入是否落在 0 到 UINT_MAX ？

解决方案

两件事：

• 检查无符号整数是< 0或> UINT_MAX是无意义的，因为它永远不能达到该值！




• 我可以想到的唯一解决方案是捕捉在字符串中输入，然后使用老式的strtoul（），在溢出时设置errno。

<

  #include< stdlib.h> 
 
 unsigned long number; 
 std :: string numbuf; 
 cin>> numbuf; 
 number = strtoul（numbuf.c_str（），0，10）; 
 if（ULONG_MAX == number&& ERANGE == errno）
 {
 std :: cerr< 数字太大了！ << std :: endl; 
} 
  

注意：strtoul返回unsigned long;没有函数strtou（），返回一个unsigned int。

I am trying to read an unsigned int using cin as follows:

#include <limits.h>
#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
    unsigned int number;

    // UINT_MAX = 4294967295
    cout << "Please enter a number between 0 and " << UINT_MAX << ":" << endl;

    cin >> number;

    // Check if the number is a valid unsigned integer
    if ((number < 0) || ((unsigned int)number > UINT_MAX))
    {
        cout << "Invalid number." << endl;
        return -1;
    }
    return 0;
}

However, whenever I enter a value greater than the upper limit of unsigned integer (UINT_MAX), the program displays 3435973836. How do I check if the input given by user falls between 0 to UINT_MAX?

解决方案

Two things:

• Checking if an unsigned integer is < 0 or > UINT_MAX is pointless, since it can never reach that value! Your compiler probably already complains with a warning like "comparison is always false due to limited range of type".

• The only solution I can think of is catching the input in a string, then use old-fashioned strtoul() which sets errno in case of overflow.

I.e.:

#include <stdlib.h>

unsigned long number;
std::string numbuf;
cin >> numbuf;
number = strtoul(numbuf.c_str(), 0, 10);
if (ULONG_MAX == number && ERANGE == errno)
{
    std::cerr << "Number too big!" << std::endl;
}

Note: strtoul returns an unsigned long; there's no function strtou(), returning an unsigned int.

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