如果 std::string 确实是整数，如何检查它?

2022-01-13 00:00:00 string integer type-conversion typechecking c++

以下代码将 std::string 转换为 int，问题在于它无法区分真正的整数或随机字符串.有没有系统的方法来处理这样的问题?

The following code converts an std::string to int and the problem lies with the fact that it cannot discern from a true integer or just a random string. Is there a systematic method for dealing with such a problem?

#include <cstring>
#include <iostream>
#include <sstream>

int main()
{
    std::string str =  "H";

    int int_value;
    std::istringstream ss(str);
    ss >> int_value;

    std::cout<<int_value<<std::endl;

    return 0;
}

编辑:这是我喜欢的解决方案，因为它非常简约和优雅！它不适用于负数，但无论如何我只需要正数.

EDIT: This is the solution that I liked because it is very minimal and elegant! It doesn't work for negative numbers but I only needed positive ones anyways.

#include <cstring>
#include <iostream>
#include <sstream>

int main()
{
    std::string str =  "2147483647";

    int int_value;
    std::istringstream ss(str);

    if (ss >> int_value)
        std::cout << "Hooray!" << std::endl;

    std::cout<<int_value<<std::endl;


    str =  "-2147483648";
    std::istringstream negative_ss(str);

    if (ss >> int_value)
        std::cout << "Hooray!" << std::endl;

    std::cout<<int_value<<std::endl;

    return 0;
}

推荐答案

WhozCraig 的方法要好得多，我想使用 C++ FAQ 使用如下:

WhozCraig's approach is much nicer and I wanted to expand on it using the approach that the C++ FAQ uses which is as follows:

#include <iostream>
#include <sstream>
#include <string>
#include <stdexcept>

class BadConversion : public std::runtime_error {
public:
  BadConversion(std::string const& s)
    : std::runtime_error(s)
    { }
};



inline int convertToInt(std::string const& s,
                              bool failIfLeftoverChars = true)
{
  std::istringstream i(s);
  int x;
  char c;
  if (!(i >> x) || (failIfLeftoverChars && i.get(c)))
    throw BadConversion("convertToInt("" + s + "")");
  return x;
}


int main()
{
    std::cout << convertToInt( "100" ) << std::endl ;
    std::cout << convertToInt( "-100" ) << std::endl ;
    std::cout << convertToInt( "  -100" ) << std::endl ;
    std::cout << convertToInt( "  -100  ", false ) << std::endl ;

    // The next two will fail
    std::cout << convertToInt( "  -100  ", true ) << std::endl ;
    std::cout << convertToInt( "H" ) << std::endl ;
}

这很健壮，并且会知道转换是否失败，您还可以选择对剩余字符进行失败.

This is robust and will know if the conversion fails, you also can optionally choose to fail on left over characters.

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