C ++:将double/float转换为字符串，保留科学计数法和精度 [英] C++: Converting a double/float to string, preserve scientific notation and precision

问题描述

我正在尝试将双精度/浮点数转换为字符串.其中一些数字包含科学符号"e"，我想在转换后保留它.我搜索了google和stackoverflow，但没有找到与我的用例匹配的答案.

I'm trying to convert double/float numbers to string. Some of these numbers contain scientific notation "e", and I want to preserve it after the conversion. I searched through google and stackoverflow and didn't find a matching answer to my use case.

以下是一些示例和预期的输出:

Here are some examples and expected output:

input: 1.7976931348623157e+308
output: "1.7976931348623157e+308"

这是一个完整的 main.cc 文件，可以编译:

Here is a full main.cc file that can be compiled:

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

template <typename T>
std::string ToString(T value) {
  std::stringstream out;
  out << std::fixed;
  out << value;
  return out.str();
}

int main () {
    double mydouble = 1.7976931348623157e+308;
    std::cout << ToString(mydouble) << std::endl;
}

-更新11:17 AM -----

--- Update 11:17AM -----

运行上面的独立代码后，不再有奇怪的字符，但是输出为长字符串格式的浮点数:

There is no more weird characters after running my standalone code above, but the output is a long string-formatted float:

179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.000000

不是预期的"1.7976931348623157e + 308".

Not the expected "1.7976931348623157e+308".

--------过时的----------------

-------- Outdated ----------------

但是输出是一个奇怪的字符串:

But the output is a weird string:

"179769313486231610000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000ÍÍÍÍÍÍÍÍýýýý««««««««««««««««îþîþîþîþ"

推荐答案

两件事:

如果要使用科学记数法，则不需要的不是固定值.相反.

Fixed isn't what you want if you want scientific notation. It's the opposite.

我编译时

#include <iostream>
#include <sstream>

template <typename T>
inline std::string ToString(T value) {
    std::stringstream out;
    out << std::fixed;  
    out << value;
    return out.str();
}
int main()  
{
    double mydouble = 1.7976931348623157e+308; 
    std::cout << ToString(mydouble) << std::endl; 
}

我知道

179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.000000

这是正确的，这意味着您的C ++编译器或标准库中存在错误.

which is right, which means there's a bug in your C++ compiler or standard library.

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