C++ 使用 << 和 double 时防止 ostream 中的科学记数法
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Prevent scientific notation in ostream when using << with double
提问by DogDog
I need to prevent my double to print in scientific notation in my file,
我需要防止我的 double 在我的文件中以科学记数法打印，
when I do this
当我这样做时
outfile << X;
回答by davecoulter
To set formatting of floating variables you can use a combination of setprecision(n), showpointand fixed. In order to use parameterized stream manipulators like setprecision(n)you will have to include the iomanip library:
要设置浮动变量的格式，您可以使用setprecision(n),showpoint和的组合fixed。为了使用参数化的流操作器，setprecision(n)你必须包含 iomanip 库：
#include <iomanip>
setprecision(n): will constrain the floating-output to nplaces, and once you set it, it is set until you explicitly unset it for the remainder of the stream output.
setprecision(n): 将浮动输出限制到n位置，一旦你设置它，它就会被设置，直到你为流输出的其余部分明确取消它为止。
fixed: will enforce that all floating-point numbers are output the same way. So if your precision is set to 4 places, 6.2, and 6.20will both be output as:
fixed: 将强制所有浮点数以相同方式输出。因此，如果您的精度设置为 4 位，6.2, 和6.20都将输出为：
6.2000
6.2000
showpoint: will force the decimal portions of a floating-point variable to be displayed, even if it is not explicitly set. For instance, 4will be output as:
showpoint: 将强制显示浮点变量的小数部分，即使它没有明确设置。例如，4将输出为：
4.0
Using them all together:
一起使用它们：
outfile << fixed << showpoint;
outfile << setprecision(4);
outfile << x;
回答by Rozuur
Here's an example of usage http://cplus.about.com/od/learning1/ss/clessontwo_4.htm
这是一个使用示例 http://cplus.about.com/od/learning1/ss/clessontwo_4.htm
as per your question use
根据您的问题使用
std::cout << std::fixed << a << std::endl;
回答by matiu
All the above answers were useful, but none directly answer the question.
以上所有答案都很有用，但没有一个直接回答问题。
outfile.setf(ios_base::fixed);
outfile << x;
I found the answer in @moogs link: http://www.cplusplus.com/reference/iostream/ios_base/fmtflags/
我在@moogs 链接中找到了答案：http://www.cplusplus.com/reference/iostream/ios_base/fmtflags/
Here's a demo program: http://ideone.com/FMxRp1
这是一个演示程序：http: //ideone.com/FMxRp1
