C++ 一个字符串占用多少字节？一个字符？

How many bytes does a string take? A char?

提问by Moshe

I'm doing a review of my first semester C++ class, and I think I missing something. How many bytes does a string take up? A char?

我正在复习我第一学期的 C++ 课，我想我错过了一些东西。一个字符串占用多少字节？一个字符？

The examples we were given are, some being character literals and some being strings:

我们给出的例子是，一些是字符文字，一些是字符串：

'n', "n", '\n', "\n", "\\n", ""

'n', "n", '\n', "\n", "\\n", ""

I'm particularly confused by the usage of newlines in there.

我对那里的换行符的使用感到特别困惑。

回答by fredoverflow

#include <iostream>

int main()
{
        std::cout << sizeof 'n'   << std::endl;   // 1
        std::cout << sizeof "n"   << std::endl;   // 2
        std::cout << sizeof '\n'  << std::endl;   // 1
        std::cout << sizeof 'n'   << std::endl;   // 1
        std::cout << sizeof "\n"  << std::endl;   // 2
        std::cout << sizeof "\n" << std::endl;   // 3
        std::cout << sizeof "n"   << std::endl;   // 2
}

Single quotes indicate characters, double quotes indicate C-style strings with an invisible NUL terminator.

单引号表示字符，双引号表示带有不可见 NUL 终止符的 C 样式字符串。

\n(line break) is only a single char, and so is \\(backslash). \\nis just a backslash followed by n.

\n（换行符）只是一个字符，\\（反斜杠）也是如此。\\n只是一个反斜杠后跟 n。

回答by gztomas

• 'n': is not a string, is a literal char, one byte, the ascii code for character n.
• "n": string, two bytes, one for n and one for the null character every string has at the end.
• "\n": two bytes as \n stand for "new line" which takes one byte, plus one byte for the null char.
• '\n': same as the first, literal char, not a string, one byte.
• "\\n": three bytes.. one for \, one for newline and the null character
• "": one byte, just the null character.

• 'n': 不是字符串，是文字字符，一个字节，字符 n 的 ascii 代码。
• "n": 字符串，两个字节，一个用于 n，一个用于每个字符串末尾的空字符。
• "\n": 两个字节作为 \n 代表“换行”，它需要一个字节，加上一个字节的空字符。
• '\n': 与第一个文字字符相同，不是字符串，一个字节。
• "\\n": 三个字节..一个用于\，一个用于换行符和空字符
• "": 一个字节，只是空字符。

回答by ildjarn

• A char, by definition, takes up one byte.
• Literals using 'are char literals; literals using "are string literals.
• A string literal is implicitly null-terminated, so it will take up one more byte than the observable number of characters in the literal.
• \is the escape character and \nis a newline character.

• A char，根据定义，占用一个字节。
• 使用'的文字是字符文字；使用"的文字是字符串文字。
• 字符串文字是隐式以空字符结尾的，因此它将比文字中可观察到的字符数多占用一个字节。
• \是转义字符，\n是换行符。

Put these together and you should be able to figure it out.

把这些放在一起，你应该能够弄清楚。

回答by Wojciech Cierpucha

The following will take x consecutive chars in memory:

以下将在内存中占用 x 个连续字符：

'n' - 1 char (type char)
"n" - 2 chars (above plus zero character) (type const char[2])
'\n' - 1 char
"\n" - 2 chars
"\n" - 3 chars ('\', 'n', and zero)
"" - 1 char

edit: formatting fixed

编辑：格式固定

edit2: I've written something very stupid, thanks Mooing Duck for pointing that out.

编辑 2：我写了一些非常愚蠢的东西，感谢 Mooing Duck 指出这一点。

回答by wallyk

You appear to be referring to string constants. And distinguishing them from character constants.

您似乎指的是字符串常量。并将它们与字符常量区分开来。

A charis one byte on all architectures. A character constant uses the single quote delimiter '.

Achar在所有架构上都是一个字节。字符常量使用单引号分隔符'。

A string is a contiguous sequence of characters with a trailing NUL character to identify the end of string. A string uses double quote characters '"'.

字符串是一个连续的字符序列，带有尾随的 NUL 字符来标识字符串的结尾。字符串使用双引号字符 '"'。

Also, you introduce the C string constant expression syntax which uses blackslashes to indicate special characters. \nis one character in a string constant.

此外，您还介绍了使用黑斜线表示特殊字符的 C 字符串常量表达式语法。 \n是字符串常量中的一个字符。

So for the examples 'n', "n", '\n', "\n":
'n'is one character
"n"is a string with one character, but it takes two characters of storage (one for the letter nand one for the NUL
'\n'is one character, the newline (ctrl-J on ASCII based systems)
"\n"is one character plus a NUL.

因此对于示例'n', "n", '\n', "\n"：
'n'一个字符是一个字符
"n"的字符串，但它需要两个存储字符（一个用于字母n，一个用于 NUL
'\n'是一个字符，换行符（基于 ASCII 的系统上的 ctrl-J）
"\n"是一个字符加上一个 NUL。

I leave the others to puzzle out based on those.

我让其他人根据这些来解谜。

回答by Mooing Duck

'n'-> One char. A charis always 1 byte. This is not a string.
"n"-> A string literal, containing one nand one terminating NULL char. So 2 bytes.
'\n'-> One char, A charis always 1 byte. This is not a string.
"\n"-> A string literal, containing one \nand one terminating NULL char. So 2 bytes.
"\\n"-> A string literal, containing one \, one '\n', and one terminating NULL char. So 3 bytes.
""-> A string literal, containing one terminating NULL char. So 1 byte.

'n'-> 一char。Achar总是 1 个字节。这不是字符串。
"n"-> 一个字符串文字，包含一个n和一个终止 NULL char。所以2个字节。
'\n'-> 一char，Achar总是 1 个字节。这不是字符串。
"\n"-> 一个字符串文字，包含一个\n和一个终止 NULL char。所以2个字节。
"\\n"-> 一个字符串文字，包含一个\、一个 '\n' 和一个终止 NULL char。所以3个字节。
""-> 一个字符串文字，包含一个终止 NULL char。所以1个字节。

回答by triclosan

'n'   - 0x6e
"n"   - 0x6e00
'\n'  - 0x0a
"\n"  - 0x0a00
"\n" - 0x5c6e00
""    - 0x00

回答by Jonathan Wood

The number of bytes a string takes up is equal to the number of characters in the string plus 1 (the terminator), times the number of bytes per character. The number of bytes per character can vary. It is 1 byte for a regular chartype.

字符串占用的字节数等于字符串中的字符数加 1（终止符）乘以每个字符的字节数。每个字符的字节数可能会有所不同。对于常规char类型，它是 1 个字节。

All your examples are one character long except for the second to last, which is two, and the last, which is zero. (Some are of type charand only define a single character.)

除了倒数第二个是 2 和最后一个是 0 之外，所有示例都是一个字符长。（有些是类型char并且只定义一个字符。）