C++ 四舍五入到小数点后两位
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Rounding to 2 decimal points
提问by averageUsername123
I've used the following to round my values to 2 decimal points:
我使用以下内容将我的值四舍五入到 2 个小数点：
x = floor(num*100+0.5)/100;
and this seems to work fine; except for values like "16.60", which is "16.6".
这似乎工作正常；除了像“16.60”这样的值，即“16.6”。
I want to output this value like "16.60".
我想输出这个值，比如“16.60”。
The way I'm outputting values is the following:
我输出值的方式如下：
cout setw(12) << round(payment);
I've tried the following:
我尝试了以下方法：
cout setw(12) << setprecision(2) << round(payment);
But that gave me answers like
但这给了我答案
1.2e+02
How can I output the values correctly?
如何正确输出值？
回答by billz
This is because std::setprecisiondoesn't set the digits after the decimal point but the significant digits if you don't change the floating point format to use a fixed number of digits after the decimal point. To change the format, you have to put std::fixedinto your output stream:
这是因为std::setprecision如果您不更改浮点格式以使用小数点后的固定位数，则不会设置小数点后的数字而是有效数字。要更改格式，您必须将std::fixed放入输出流中：
double a = 16.6;
std::cout << std::fixed << std::setprecision(2) << a << std::endl;
回答by gerrytan
you can use printf / sprintf or other similar functions. Following code will format floating point value into two digits after decimals. Refer to the printf manual for more formatting info
您可以使用 printf / sprintf 或其他类似功能。以下代码将浮点值格式化为小数点后两位。有关更多格式信息，请参阅 printf 手册
float f = 1.234567
printf("%.2f\n", f);
回答by Drew Dormann
From Trevor Boyd Smith's comment:
来自特雷弗博伊德史密斯的评论：
If you are allergic to printf and friends there is the type safe C++ version in
#include <boost/format.hpp>which you can use to do:
如果您对 printf 和朋友过敏，则
#include <boost/format.hpp>可以使用类型安全的 C++ 版本来执行以下操作：
float f = 1.234567;
cout << boost::format("%.2f") % f << endl;
