在 C++ 中使用 boost::lexical_cast 将双精度转换为字符串？
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Convert double to string using boost::lexical_cast in C++?
提问by perusopersonale
I' d like to use lexical_castto convert a float to a string. Usually it works fine, but I have some problems with numbers without decimal. How can I fix number of decimal shown in the string?
我想用来lexical_cast将浮点数转换为字符串。通常它工作正常，但我对没有小数的数字有一些问题。如何修复字符串中显示的小数位数？
Example:
例子：
double n=5;
string number;
number = boost::lexical_cast<string>(n);
Result number is 5, I need number 5.00.
结果编号是5，我需要编号5.00。
回答by Mic
From the documentation for boost lexical_cast:
来自boost lexical_cast的文档：
For more involved conversions, such as where precision or formatting need tighter control than is offered by the default behavior of lexical_cast, the conventional stringstream approach is recommended. Where the conversions are numeric to numeric, numeric_cast may offer more reasonable behavior than lexical_cast.
对于更复杂的转换，例如精度或格式需要比 lexical_cast 的默认行为提供的更严格的控制，建议使用传统的 stringstream 方法。在数字到数字的转换中，numeric_cast 可能提供比 lexical_cast 更合理的行为。
Example:
例子：
#include <sstream>
#include <iomanip>
int main() {
std::ostringstream ss;
double x = 5;
ss << std::fixed << std::setprecision(2);
ss << x;
std::string s = ss.str();
return 0;
}
回答by Etienne Monette
Have a look at boost::format library. It merges the usability of printf with type safety of streams. For speed, I do not know, but I doubt it really matters nowadays.
看看 boost::format 库。它结合了 printf 的可用性和流的类型安全性。至于速度，我不知道，但我怀疑现在它真的很重要。
#include <boost/format.hpp>
#include <iostream>
int main()
{
double x = 5.0;
std::cout << boost::str(boost::format("%.2f") % x) << '\n';
}
回答by D.Shawley
If you need complex formatting, use std::ostringstreaminstead. boost::lexical_castis meant for "simple formatting".
如果您需要复杂的格式，请std::ostringstream改用。 boost::lexical_cast用于“简单格式化”。
std::string
get_formatted_value(double d) {
std::ostringstream oss;
oss.setprecision(3);
oss.setf(std::ostringstream::showpoint);
oss << d;
return oss.str();
}
回答by hidayat
you can also use sprintf, which is faster then ostringstream
您还可以使用 sprintf，它比 ostringstream 更快
#include <cstdio>
#include <string>
using namespace std;
int main()
{
double n = 5.0;
char str_tmp[50];
sprintf(str_tmp, "%.2f", n);
string number(str_tmp);
}
