char c2[]={′\x10′, ′xa′, ′\x8′} 这里的'xa'是什么意思？

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char c2={′\x10′, ′xa′, ′\x8′}
这里的'xa'是什么意思？

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cornfield2012 2014-02-28

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char c2={′\x10′, ′xa′, ′\x8′};字符型变量只占一个字节，可以用花括号去定义，你这样可你这样定义了多个变量取得的第一个字符，也就是'\x10'；如果用char c2='xa'；编译器会警告多字符，但没错误，因为开始写入c2的是x然后被a覆盖掉了，所以打印出来的是a。

ForestDB 2014-02-26

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确定不是'\xa'？如果没有笔误的话，就是multi-character constant，非标准的东西，编译会给warning的。

rendason 2014-02-26

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这应该是转义字符那得知识，如果在字符串中加入十六进制数，用\x加十六进制数，如果想加入八进制数，用\o加八进制数

ameyume 2014-02-26

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'xa'就是16进制的'0xa'的意思吧。
验证代码如下：

void main()

{

    char c1 = {'\x10'};

	printf("c1:%c\n", c1);



    char c2 = {'xa'};

	printf("c2:%c\n", c2);



	char c20 = 'xa';

	printf("c20:%c\n", c20);



	char c21 = {'0xa'};

	printf("c21:%c\n", c21);



	char c22 = {'a'};

	printf("c22:%c\n", c22);



    char c3 = {'\x8'};

	printf("c3:[%c]\n", c3);



	char c4 = {'\x10', 'xa', '\x8'};

	printf("c4:%c\n", c4);



}

编译警告如下：

gcc test.c -o test
test.c: 在函数‘main’中:
test.c:9:16: 警告：多字节字符常量 [-Wmultichar]
test.c:9:5: 警告：隐式常量转换溢出 [-Woverflow]
test.c:12:13: 警告：多字节字符常量 [-Wmultichar]
test.c:12:2: 警告：隐式常量转换溢出 [-Woverflow]
test.c:15:14: 警告：多字节字符常量 [-Wmultichar]
test.c:15:2: 警告：隐式常量转换溢出 [-Woverflow]
test.c:24:21: 警告：多字节字符常量 [-Wmultichar]
test.c:24:2: 警告：标量初始值设定项中有多余元素 [默认启用]
test.c:24:2: 警告： (在‘c4’的初始化附近) [默认启用]
test.c:24:2: 警告：标量初始值设定项中有多余元素 [默认启用]
test.c:24:2: 警告： (在‘c4’的初始化附近) [默认启用]

运行结果如下：

dbzhang800 2014-02-26

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额，看错了，c2是一个字符而不是数组？？

dbzhang800 2014-02-26

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编译过去应该没问题，一个字符常量中包含多个字符是 implementation-defined 的行为。搜 multi-character character 应该找到很多相关内容

赵4老师 2014-02-26

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C++ Character Constants Character constants are one or more members of the “source character set,” the character set in which a program is written, surrounded by single quotation marks ('). They are used to represent characters in the “execution character set,” the character set on the machine where the program executes. Microsoft Specific For Microsoft C++, the source and execution character sets are both ASCII. END Microsoft Specific There are three kinds of character constants: Normal character constants Multicharacter constants Wide-character constants Note Use wide-character constants in place of multicharacter constants to ensure portability. Character constants are specified as one or more characters enclosed in single quotation marks. For example: char ch = 'x'; // Specify normal character constant. int mbch = 'ab'; // Specify system-dependent // multicharacter constant. wchar_t wcch = L'ab'; // Specify wide-character constant. Note that mbch is of type int. If it were declared as type char, the second byte would not be retained. A multicharacter constant has four meaningful characters; specifying more than four generates an error message. Syntax character-constant : 'c-char-sequence' L'c-char-sequence' c-char-sequence : c-char c-char-sequence c-char c-char : any member of the source character set except the single quotation mark ('), backslash (\), or newline character escape-sequence escape-sequence : simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence simple-escape-sequence : one of \' \" \? \\ \a \b \f \n \r \t \v octal-escape-sequence : \octal-digit \octal-digit octal-digit \octal-digit octal-digit octal-digit hexadecimal-escape-sequence : \xhexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit Microsoft C++ supports normal, multicharacter, and wide-character constants. Use wide-character constants to specify members of the extended execution character set (for example, to support an international application). Normal character constants have type char, multicharacter constants have type int, and wide-character constants have type wchar_t. (The type wchar_t is defined in the standard include files STDDEF.H, STDLIB.H, and STRING.H. The wide-character functions, however, are prototyped only in STDLIB.H.) The only difference in specification between normal and wide-character constants is that wide-character constants are preceded by the letter L. For example: char schar = 'x'; // Normal character constant wchar_t wchar = L'\x81\x19'; // Wide-character constant Table 1.2 shows reserved or nongraphic characters that are system dependent or not allowed within character constants. These characters should be represented with escape sequences. Table 1.2 C++ Reserved or Nongraphic Characters Character ASCII Representation ASCII Value Escape Sequence Newline NL (LF) 10 or 0x0a \n Horizontal tab HT 9 \t Vertical tab VT 11 or 0x0b \v Backspace BS 8 \b Carriage return CR 13 or 0x0d \r Formfeed FF 12 or 0x0c \f Alert BEL 7 \a Backslash \ 92 or 0x5c \\ Question mark ? 63 or 0x3f \? Single quotation mark ' 39 or 0x27 \' Double quotation mark " 34 or 0x22 \" Octal number ooo — \ooo Hexadecimal number hhh — \xhhh Null character NUL 0 \0 If the character following the backslash does not specify a legal escape sequence, the result is implementation defined. In Microsoft C++, the character following the backslash is taken literally, as though the escape were not present, and a level 1 warning (“unrecognized character escape sequence”) is issued. Octal escape sequences, specified in the form \ooo, consist of a backslash and one, two, or three octal characters. Hexadecimal escape sequences, specified in the form \xhhh, consist of the characters \x followed by a sequence of hexadecimal digits. Unlike octal escape constants, there is no limit on the number of hexadecimal digits in an escape sequence. Octal escape sequences are terminated by the first character that is not an octal digit, or when three characters are seen. For example: wchar_t och = L'\076a'; // Sequence terminates at a char ch = '\233'; // Sequence terminates after 3 characters Similarly, hexadecimal escape sequences terminate at the first character that is not a hexadecimal digit. Because hexadecimal digits include the letters a through f (and A through F), make sure the escape sequence terminates at the intended digit. Because the single quotation mark (') encloses character constants, use the escape sequence \' to represent enclosed single quotation marks. The double quotation mark (") can be represented without an escape sequence. The backslash character (\) is a line-continuation character when placed at the end of a line. If you want a backslash character to appear within a character constant, you must type two backslashes in a row (\\). (SeePhases of Translation in the Preprocessor Reference for more information about line continuation.)

Falleyes 2014-02-26

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你这一句能编译过去？

​char c2[]={′\x10′, ′xa′, ′\x8′} 这里的'xa'是什么意思？

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char c2[]={′\x10′, ′xa′, ′\x8′} 这里的'xa'是什么意思？