“a”和“a”之间的区别是什么？ [英] What is the difference between 'a' and "a"?

问题描述

我在学习C ++，有一个问题，我找不到答案。

char 常量（使用单引号）和字符串常量（带双引号）？

所有与char数组相关的搜索结果vs std :: string 。我之后是'a'和之间的区别。

执行以下操作会有所不同：

  cout< 一个; 
 cout<< '一个'; 
  

解决方案

'a' code>是字符文字。它是 char 类型，在大多数系统上的值为97（ASCII / Latin-1 / Unicode编码的字母 a ）。





a是一个字符串文字。它的类型为 const char [2] ，并引用一个数组2 char c>'a'和'\0'。在大多数但不是全部的上下文中，对a 的引用将隐式转换为指向字符串第一个字符的指针。

两者

  cout< '一个'; 
  

和

  cout< 一个; 
  

恰好产生相同的输出，但是出于不同的原因。第一个打印单个字符值。第二个依次打印字符串的所有字符（除了结束'\0'） - 这恰好是单个字符'字符串字面量可以任意长，例如abcdefg。



< 。字符文字几乎总是只包含一个字符。 （您可以有多字符文字，例如'ab'，但是它们的值是实现定义的，并且很少有用） / p>



（在C中，你没有问过，'a'是 int 和a的类型为 char [2] code> const ））。

I am learning C++ and have got a question that I cannot find the answer to.

What is the difference between a char constant (using single quotes) and a string constant (with double quotes)?

All my search results related to char arrays vs std::string. I am after the difference between 'a' and "a".

Would there be a difference in doing the following:

cout << "a";
cout << 'a';

解决方案

'a' is a character literal. It's of type char, with the value 97 on most systems (the ASCII/Latin-1/Unicode encoding for the letter a).

"a" is a string literal. It's of type const char[2], and refers to an array of 2 chars with values 'a' and '\0'. In most, but not all, contexts, a reference to "a" will be implicitly converted to a pointer to the first character of the string.

Both

cout << 'a';

and

cout << "a";

happen to produce the same output, but for different reasons. The first prints a single character value. The second successively prints all the characters of the string (except for the terminating '\0') -- which happens to be the single character 'a'.

String literals can be arbitrarily long, such as "abcdefg". Character literals almost always contain just a single character. (You can have multicharacter literals, such as 'ab', but their values are implementation-defined and they're very rarely useful.)

(In C, which you didn't ask about, 'a' is of type int, and "a" is of type char[2] (no const)).

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