英文:
How could I extend a format-spec for existing type (eg float) in C++?
问题
我想扩展浮点类型的格式选项，最好保留一些现有选项。例如，我想添加一个新的“type”指示符，用于带单位的测量，以便像这样编写：std::format({:.5mm}, 0.05f)，并且以precision=5打印我的数据，但也要乘以1000并以'mm'为前缀。这种操作是否可能？
英文:
I want to extend formatting options for floating-point type, preferably preserving some of the existing options. For instance, I want to add a new type specifier for the measurements with units to write like this std::format({:.5mm}, 0.05f) and get my data printed with precision=5, but also multiplied by 1000 and prefixed with 'mm'. Is that even possible?
答案1
得分: 5
基本类型如 float 的格式规范是内置的，无法扩展。
可以 将它们封装在用户定义的类型中，并对其应用任意格式。 如示例中所示，std::format("{:.5mm}", MyUnit(0.05f))，其中 MyUnit 是您的类型，具有自己的格式规范。
英文:
The formatting specification for basic types like float are built into the system; you cannot extend them.
You can wrap them in a user-defined type which you can apply whatever formatting to you like. As exemplified in the comments, std::format("{:.5mm}", MyUnit(0.05f)), where MyUnit is your type which has its own formatting specification.
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