c++ - boost::lexical_cast ("-138.8468953457983248") 抛出异常

Question

我正在尝试将此数字转换为整数。但是我抛出了一个 bad_cast 异常。我不确定发生了什么。

Answer 1

那是因为值(value)

-138.8468953457983248

不是整数。

您需要将其转换为浮点值。

    int a = static_cast<double>("-138.21341535");
                 //     ^^^^^^   Cast to double
 // ^^^  You can assign double to an int

词法转换将尝试使用字符串中的所有字符。如果还有剩余，那就是糟糕的 Actor 阵容。当您尝试将以上内容转换为整数时，它显示为“-138”，但在生成异常的转换缓冲区中留下了“.21341535”。

#include <boost/lexical_cast.hpp>

int main()
{
    std::cout << "Try\n";
    try
    {
        std::cout << boost::lexical_cast<int>("-138.8468953457983248") << "\n";
    }
    catch(boost::bad_lexical_cast const& e)
    {
        std::cout << "Error: " << e.what() << "\n";
    }
    std::cout << "Done\n";
    std::cout << "Try\n";
    try
    {
        std::cout << boost::lexical_cast<double>("-138.8468953457983248") << "\n";
    }
    catch(boost::bad_lexical_cast const& e)
    {
        std::cout << "Error: " << e.what() << "\n";
    }
    std::cout << "Done\n";
}

这个:

> g++ lc.cpp
> ./a.out 
Try
Error: bad lexical cast: source type value could not be interpreted as target
Done
Try
-138.847
Done