C++ 将数字格式化为特定的 QString 格式
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Format a Number to a specific QString format
提问by ImGreg
I have a question about formatting a decimal number to a certain QString format. Basically, I have an input box in my program that can take any values. I want it to translate the value in this box to the format "+05.30" (based on the value). The value will be limited to +/-99.99.
我有一个关于将十进制数格式化为某种 QString 格式的问题。基本上，我的程序中有一个可以接受任何值的输入框。我希望它将此框中的值转换为格式“+05.30”（基于值）。该值将限制为 +/-99.99。
Some examples include:
一些例子包括：
.2 --> +00.02
.2 --> +00.02
-1.5 --> -01.50
-1.5 --> -01.50
9.9 --> +09.90
9.9 --> +09.90
I'm thinking of using a converter like this, but it will have some obvious issues (no leading 0, no leading + sign).
我正在考虑使用这样的转换器，但它会有一些明显的问题（没有前导 0，没有前导 + 符号）。
QString temp = QString::number(ui.m_txtPreX1->text().toDouble(), 'f', 2);
This question had some similarities, but doesn't tie together both front and back end padding.
这个问题有一些相似之处，但并没有将前端和后端填充联系在一起。
Convert an int to a QString with zero padding (leading zeroes)
Any ideas of how to approach this problem? Your help is appreciated! Thanks!
关于如何解决这个问题的任何想法？感谢您的帮助！谢谢！
回答by
I don't think you can do that with any QString method alone (either numberor arg). Of course you could add zeros and signs manually, but I would use the good old sprintf:
我认为您不能单独使用任何 QString 方法（number或arg）来做到这一点。当然，您可以手动添加零和符号，但我会使用旧的 sprintf：
double value = 1.5;
QString text;
text.sprintf("%+06.2f", value);
Edit:Simplified the code according to alexisdm's comment.
编辑：根据 alexisdm 的评论简化了代码。
回答by alexisdm
You just have to add the sign manually:
您只需要手动添加符号：
QString("%1%2").arg(x < 0 ? '-' : '+').arg(qFabs(x),5,'f',2,'0');
Edit: The worst thing is that there is actually an internal function, QLocalePrivate:doubleToStringthat supports the forced sign and the padding at both end as the same time but it is only used with these options in QString::sprintf, and not:
编辑：最糟糕的是，实际上有一个内部函数，QLocalePrivate:doubleToString它同时支持强制符号和两端的填充，但它仅与 中的这些选项一起使用QString::sprintf，而不是：
QTextStreamand its<<operator, which can force the sign to show, but not the width orQString::arg, which can force the width but not the sign.
QTextStream及其<<运算符，可以强制显示符号，但不能强制显示宽度或QString::arg，这可以强制宽度但不能强制符号。
But for QTextStreamthat might be a bug.
但这QTextStream可能是一个错误。
