C / C ++中字符（&#39；a&#39；）的大小

ゞ浴缸里的玫瑰 2022-11-27 15:55 160阅读 0赞

本文翻译自：[Size of character ('a') in C/C++][Size of character _a_ in C_C]

*What is the size of character in C and C++ ?* **C和C ++中的字符大小是多少？** *As far as I know the size of char is 1 byte in both C and C++.* **据我所知，在C和C ++中char的大小均为1个字节。**

***[In C:][In C]*** **[在C中：][In C]**

#include <stdio.h>
    int main()
    {
        printf("Size of char : %d\n", sizeof(char));
        return 0;
    }

***[In C++:][In C 1]*** **[在C ++中：][In C 1]**

#include <iostream>
    int main()
    {
        std::cout << "Size of char : " << sizeof(char) << "\n";
        return 0;
    }

*No surprises, both of them gives the output : `Size of char : 1`* **毫不奇怪，它们都给出了输出： `Size of char : 1`**

*Now we know that characters are represented as `'a'` , `'b'` , `'c'` , `'|'`* **现在我们知道字符被表示为`'a'` ， `'b'` ， `'c'` ， `'|'`** *,... So I just modified the above codes to these:* **，...所以我刚刚将以上代码修改为：**

***In C:*** **在C中：**

#include <stdio.h>
    int main()
    {
        char a = 'a';
        printf("Size of char : %d\n", sizeof(a));
        printf("Size of char : %d\n", sizeof('a'));
        return 0;
    }

***[Output:][Output]*** **[输出：][Output]**

Size of char : 1
    Size of char : 4

***In C++:*** **在C ++中：**

#include <iostream>
    int main()
    {
        char a = 'a';
        std::cout << "Size of char : " << sizeof(a) << "\n";
        std::cout << "Size of char : " << sizeof('a') << "\n";
        return 0;
    }

***[Output:][Output 1]*** **[输出：][Output 1]**

Size of char : 1
    Size of char : 1

***Why the `sizeof('a')` returns different values in C and C++?*** **为什么`sizeof('a')`在C和C ++中返回不同的值？**

--------------------

### \#1楼 ###

参考：[https://stackoom.com/question/97ht/C-C-中字符-a-的大小][https_stackoom.com_question_97ht_C-C-_-a-]

--------------------

### \#2楼 ###

*As Paul stated, it's because `'a'` is an `int` in C but a `char` in C++.* **正如保罗所说，这是因为`'a'`在C语言中是`int` ，而在C ++中是`char` 。**

*I cover that specific difference between C and C++ in something I wrote a few years ago, at: [http://david.tribble.com/text/cdiffs.htm][http_david.tribble.com_text_cdiffs.htm]* **我在几年前写的文章中介绍了C和C ++之间的特定区别： [http][http_david.tribble.com_text_cdiffs.htm] ： [//david.tribble.com/text/cdiffs.htm][http_david.tribble.com_text_cdiffs.htm]**

--------------------

### \#3楼 ###

*In C, the type of a character constant like `'a'` is actually an `int` , with size of 4 (or some other implementation-dependent value).* **在C语言中，像`'a'`这样的字符*常量*的类型实际上是一个`int` ，其大小为4（或其他一些与实现相关的值）。** *In C++, the type is `char` , with size of 1. This is one of many small differences between the two languages.* **在C ++中，类型为`char` ，大小为1。这是两种语言之间的许多小差异之一。**

--------------------

### \#4楼 ###

*In C the type of character literals are **int** and **char** in C++.* **在C语言中，字符文字的类型在C ++中为int和char 。** *This is in C++ required to **support function overloading** .* **这是C ++中支持函数重载所必需的。** *See this example:* **请参阅以下示例：**

void foo(char c)
    {
        puts("char");
    }
    void foo(int i)
    {
        puts("int");
    }
    int main()
    {
        foo('i');
        return 0;
    }

*Output:* **输出：**

char

--------------------

### \#5楼 ###

***In C language** , character literal is not a `char` type.* **在C语言中 ，字符文字不是`char`类型。** *C considers character literal as integer.* **C将字符文字视为整数。** *So, there is no difference between `sizeof('a')` and `sizeof(1)` .* **因此， `sizeof('a')`和`sizeof(1)`之间没有区别。**

*So, the sizeof character literal is equal to sizeof integer in C.* **因此，字符文字的sizeof等于C中的sizeof整数。**

***In C++ language** , character literal is type of `char` .* **在C ++语言中 ，字符文字是`char`类型。** *The [cppreference][] say's:* **[cppreference][]说的是：**

> *1) **narrow character literal or ordinary character literal, eg `'a'` or `'\\n'` or `'\\13'` .*** **1） 窄字符文字或普通字符文字，例如`'a'`或`'\\n'`或`'\\13'` 。** ***Such literal has type `char`** and the value equal to the representation of c-char in the execution character set.* **这种文字的类型为`char` ，其值等于执行字符集中c-char的表示形式。** *If c-char is not representable as a single byte in the execution character set, the literal has type int and implementation-defined value.* **如果c-char在执行字符集中不能表示为单个字节，则文字具有int类型和实现定义的值。**

*So, in C++ character literal is a type of `char` .* **因此，在C ++中，字符文字是`char` 。** *so, size of character literal in C++ is one byte.* **因此，C ++中字符文字的大小为1个字节。**

*Alos, In your programs, you have used wrong format specifier for `sizeof` operator.* **Alos，在您的程序中，您为`sizeof`运算符使用了错误的格式说明符。**

***C11 §7.21.6.1 (P9) :*** **C11§7.21.6.1（P9）：**

> *If a conversion specification is invalid, the behavior is undefined.275) **If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.*** **如果转换规范无效，则行为是不确定的。275） 如果任何参数不是对应转换规范的正确类型，则行为是不确定的。**

*So, you should use `%zu` format specifier instead of `%d` , otherwise it is undefined behaviour in C.* **因此，您应该使用`%zu`格式说明符而不是`%d` ，否则它在C中是未定义的行为。**

[Size of character _a_ in C_C]: https://oldbug.net/q/97ht/Size-of-character-a-in-C-C
[In C]: https://web.archive.org/web/20000000000000/http://www.ideone.com/e3Yo1Kyf
[In C 1]: https://web.archive.org/web/20000000000000/http://www.ideone.com/uG4Qodfo
[Output]: https://web.archive.org/web/20000000000000/http://www.ideone.com/Y11gm1lw
[Output 1]: https://web.archive.org/web/20000000000000/http://www.ideone.com/b00pdptc
[https_stackoom.com_question_97ht_C-C-_-a-]: https://stackoom.com/question/97ht/C-C-%E4%B8%AD%E5%AD%97%E7%AC%A6-a-%E7%9A%84%E5%A4%A7%E5%B0%8F
[http_david.tribble.com_text_cdiffs.htm]: http://david.tribble.com/text/cdiffs.htm#C99-char-literal
[cppreference]: http://en.cppreference.com/w/cpp/language/character_literal