使用 C++ 输出运算符打印前导零？
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Print leading zeros with C++ output operator?
提问by Frank
How can I format my output in C++? In other words, what is the C++ equivalent to the use of printflike this:
如何在 C++ 中格式化我的输出？换句话说，什么是 C++ 等价于使用printf这样的：
printf("%05d", zipCode);
I know I could just use printfin C++, but I would prefer the output operator <<.
我知道我只能printf在 C++ 中使用，但我更喜欢输出操作符<<.
Would you just use the following?
你会用下面的吗？
std::cout << "ZIP code: " << sprintf("%05d", zipCode) << std::endl;
回答by paxdiablo
This will do the trick, at least for non-negative numbers(a)such as the ZIP codes(b)mentioned in your question.
这将起到作用，至少对于非负数(a)，例如您的问题中提到的邮政编码(b)。
#include <iostream>
#include <iomanip>
using namespace std;
cout << setw(5) << setfill('0') << zipCode << endl;
// or use this if you don't like 'using namespace std;'
std::cout << std::setw(5) << std::setfill('0') << zipCode << std::endl;
The most common IO manipulators that control padding are:
控制填充的最常见的 IO 操纵器是：
std::setw(width)sets the width of the field.std::setfill(fillchar)sets the fill character.std::setiosflags(align)sets the alignment, where align is ios::left or ios::right.
std::setw(width)设置字段的宽度。std::setfill(fillchar)设置填充字符。std::setiosflags(align)设置对齐方式，其中 align 为 ios::left 或 ios::right。
And just on your preference for using <<, I'd strongly suggest you look into the fmtlibrary. This has been a great addition to our toolkit for formatting stuff and is much nicer than massively length stream pipelines, allowing you to do things like:
根据您对使用的偏好<<，我强烈建议您查看fmt图书馆。这是我们用于格式化东西的工具包的一个很好的补充，并且比大规模流管道要好得多，允许您执行以下操作：
cout << fmt::format("{:05d}", zipCode);
And it's currently being targeted by LEWG toward C++20 as well, meaning it will hopefully be a base part of the language at that point (or almost certainly later if it doesn't quite sneak in).
并且它目前也被 LEWG 定位为 C++20，这意味着它有望在那时成为该语言的基础部分（或者几乎可以肯定，如果它没有潜入的话）。
(a)If you doneed to handle negative numbers, you can use std::internalas follows:
(a)如果你确实需要处理负数，你可以使用std::internal如下：
cout << internal << setw(5) << setfill('0') << zipCode << endl;
This places the fill character betweenthe sign and the magnitude.
这会将填充字符之间的符号和幅度。
(b)This ("all ZIP codes are non-negative") is an assumption on my part but a reasonably safe one, I'd warrant :-)
(b)这（“所有邮政编码都是非负的”）是我的一个假设，但一个相当安全的假设，我保证:-)
回答by Nik Reiman
Use the setw and setfillcalls:
使用setw 和 setfill调用：
std::cout << std::setw(5) << std::setfill('0') << zipCode << std::endl;
回答by anthony
cout << setw(4) << setfill('0') << n << endl;
from:
从：
回答by Jason Newland
or,
或者，
char t[32];
sprintf_s(t, "%05d", 1);
will output 00001 as the OP already wanted to do
将输出 00001，因为 OP 已经想做
