C ++文字和Unicode [英] C++ Literals and Unicode

问题描述

C ++文字

环境:

• 操作系统:Windows 10 Pro；
• 编译器:最新的GCC.
• IDE:代码::阻止最新访问.
• 正在使用:控制台应用程序.

我对数字文字前缀的理解是，它们对确定数值类型很有用(不确定).但是，我对字符和字符串文字前缀和后缀有很多困惑.我读了很多书，花了几天的时间试图了解这种情况，但是我有更多的问题和很少的答案.所以我认为堆栈溢出可能有很多帮助.

My understanding for numerical literals prefixes is that they are useful to determine the numerical value type (not sure).However, I have a lot of confusion on character and string literals prefixes and suffixes. I read a lot and spent days trying to understand the situation, but I got more questions and few answers. so I thought stack overflow could be of a lot of help.

问:

1-字符串前缀u8 u U L的正确用法是什么?

1- What are the correct use for the string prefixes u8 u U L?

我以以下代码为例:

#include <iostream>
#include <string>
using namespace std;

int main()
{
    cout << "\n\n Hello World! (plain) \n";
    cout << u8"\n Hello World! (u8) \n";
    cout << u"\n Hello World! (u) \n";
    cout << U"\n Hello World! (U) \n";
    cout << L"\n Hello World! (plain) \n\n";

    cout << "\n\n\n";
}

输出如下:

Hello World！ (普通)

Hello World! (plain)

世界您好！ (u8)

0x47f0580x47f0840x47f0d8

0x47f0580x47f0840x47f0d8

Q2:为什么U u ans L具有这样的输出?我希望这只是确定类型而不进行编码映射(如果是).

Q2: Why U u ans L has such output? I expected it is just to determine type not do encoding mapping (if it is).

Q3是否有关于UTF-8之类的编码的简单而要点的参考.我对它们感到困惑，此外，我怀疑控制台应用程序是否能够处理它们.我认为了解它们至关重要.

Q3 Is there a simple and to the point references about encodings like UTF-8. I am confused about them, in addition I doubt that console applications is capable to deal with them. I see it is crucial to understand them.

Q4:另外，我将感谢您逐步解释自定义类型文字的参考.

Q4: Also I will appreciate a step by step reference that explain custom type literals.

推荐答案

首先查看: http://en.cppreference.com/w/cpp/language/string_literal

std::cout的类运算符<<已正确重载以打印const char*.这就是为什么打印前两个字符串的原因.

std::cout's class operator << is properly overloaded to print const char*. That is why the first two strings are printed.

cout << "\n\n Hello World! (plain) \n";
cout << u8"\n Hello World! (u8) \n";

按预期，打印 ¹ :

Hello World! (plain)

Hello World! (u8)

同时std::cout的类对于const char16_t*，const char32_t*和const wchar_t*没有特殊的<<重载，因此它将与<<的重载匹配以打印指针，这就是为什么:

Meanwhile std::cout's class has no special << overload for const char16_t*, const char32_t* and const wchar_t*, hence it will match <<'s overload for printing pointers, that is why:

cout << u"\n Hello World! (u) \n";
cout << U"\n Hello World! (U) \n";
cout << L"\n Hello World! (plain) \n\n";

打印:

0x47f0580x47f0840x47f0d8

如您所见，实际上在那里打印了3个指针值:0x47f058，0x47f084和0x47f0d8

As you can see, there are actually 3 pointer values printed there: 0x47f058, 0x47f084 and 0x47f0d8

但是，对于最后一个，您可以使用std::wcout

However, for the last one, you can get it to print properly using std::wcout

std::wcout << L"\n Hello World! (plain) \n\n";

打印

 Hello World! (plain)

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