C++ 与 std::stringstream 等效的 %02d？
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Equivalent of %02d with std::stringstream?
提问by Andreas Brinck
I want to output an integer to a std::stringstreamwith the equivalent format of printf's %02d. Is there an easier way to achieve this than:
我想以'sstd::stringstream的等效格式将整数输出到 a 。有没有比以下更简单的方法来实现这一目标：printf%02d
std::stringstream stream;
stream.setfill('0');
stream.setw(2);
stream << value;
Is it possible to stream some sort of format flags to the stringstream, something like (pseudocode):
是否可以将某种格式标志流式传输到stringstream，例如（伪代码）：
stream << flags("%02d") << value;
回答by CB Bailey
You can use the standard manipulators from <iomanip>but there isn't a neat one that does both filland widthat once:
您可以使用标准的机械手从<iomanip>但没有一个整洁的一个，做两个fill和width一次：
stream << std::setfill('0') << std::setw(2) << value;
It wouldn't be hard to write your own object that when inserted into the stream performed both functions:
编写自己的对象并不难，当插入到流中时，它会执行两个功能：
stream << myfillandw( '0', 2 ) << value;
E.g.
例如
struct myfillandw
{
myfillandw( char f, int w )
: fill(f), width(w) {}
char fill;
int width;
};
std::ostream& operator<<( std::ostream& o, const myfillandw& a )
{
o.fill( a.fill );
o.width( a.width );
return o;
}
回答by hpsMouse
You can use
您可以使用
stream<<setfill('0')<<setw(2)<<value;
回答by Marcelo Cantos
You can't do that much better in standard C++. Alternatively, you can use Boost.Format:
在标准 C++ 中你不能做得更好。或者，您可以使用 Boost.Format：
stream << boost::format("%|02|")%value;
回答by vitaut
Is it possible to stream some sort of format flags to the
stringstream?
是否可以将某种格式标志流式传输到
stringstream?
Unfortunately the standard library doesn't support passing format specifiers as a string, but you can do this with the fmt library:
不幸的是，标准库不支持将格式说明符作为字符串传递，但您可以使用fmt 库来做到这一点：
std::string result = fmt::format("{:02}", value); // Python syntax
or
或者
std::string result = fmt::sprintf("%02d", value); // printf syntax
You don't even need to construct std::stringstream. The formatfunction will return a string directly.
你甚至不需要构造std::stringstream. 该format函数将直接返回一个字符串。
Disclaimer: I'm the author of the fmt library.
免责声明：我是fmt 库的作者。
