fscanf(stdin, "%79[^\n]\n",line) 这里两个\n什么意思

陈烨GUMP_RUNRUNRUN 2014-07-12 10:58:10

第一个我大概明白一点，读取输入流中匹配到\n前的所有字符，第二个不是很清楚，这不是输出时的转义字符么。放在输入是？敲一个回车符给她？
字符数少一点来说，%20[^\n]\n, 输入Harry Potter，或者其他没到20个，然后回车会没反应，再输入一些，再回车才现实结果，但是字符还是只显示20个（这个是显然的）。如果一开始输入超过20个，敲回车就会现实结果了。这个第二个\n到底起什么作用？
程序很简单

...全文

465 15 打赏收藏转发到动态举报

写回复

用AI写文章

15 条回复

切换为时间正序

请发表友善的回复…

发表回复

ForestDB 2014-07-15

打赏
举报

读取“除了\n以外的字符”，最多读79个；完了之后输入流中还得有个\n，

赵4老师 2014-07-14

打赏
举报

引用 11 楼 gy_1518 的回复:

9、10楼全英文，亚历山大。。。

英语也是一门计算机语言的说。

陈烨GUMP_RUNRUNRUN 2014-07-14

打赏
举报

引用 13 楼 lin5161678 的回复:

你输入 123 然后按下回车表示完成输入这时候缓冲区里面存储的数据实际是 123\n 4个字符而你的 %[^\n] 表示读取除了\n以为的全部字符那么缓冲区里面的 123 就会被读走最后缓冲区里面就只剩下数据 \n 现在你知道代码里面最后一个\n是做什么的嘛 ?

额，再明白点是？？截取？那是第一个吧，第二个就是输入？可是如果有字数限制，小于字数输入要输入两个回车才显示结果

lin5161678 2014-07-14

打赏
举报

你输入 123 然后按下回车表示完成输入这时候缓冲区里面存储的数据实际是 123\n 4个字符而你的 %[^\n] 表示读取除了\n以为的全部字符那么缓冲区里面的 123 就会被读走最后缓冲区里面就只剩下数据 \n 现在你知道代码里面最后一个\n是做什么的嘛 ?

gy沧洱 2014-07-13

打赏
举报

9、10楼全英文，亚历山大。。。

赵4老师 2014-07-13

打赏
举报

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.)

赵4老师 2014-07-13

打赏
举报

scanf Width Specification width is a positive decimal integer controlling the maximum number of characters to be read from stdin. No more than width characters are converted and stored at the corresponding argument. Fewer than width characters may be read if a white-space character (space, tab, or newline) or a character that cannot be converted according to the given format occurs before width is reached. The optional prefixes h, l, I64, and L indicate the “size” of the argument (long or short, single-byte character or wide character, depending upon the type character that they modify). These format-specification characters are used with type characters in scanf or wscanf functions to specify interpretation of arguments as shown in the Table R.7. The type prefixes h, l, I64, and L are Microsoft extensions and are not ANSI-compatible. The type characters and their meanings are described in Table R.8. Table R.7 Size Prefixes for scanf and wscanf Format-Type Specifiers To Specify Use Prefix With Type Specifier double l e, E, f, g, or G long int l d, i, o, x, or X long unsigned int l u short int h d, i, o, x, or X short unsigned int h u __int64 I64 d, i, o, u, x, or X Single-byte character with scanf h c or C Single-byte character with wscanf h c or C Wide character with scanf l c or C Wide character with wscanf l c, or C Single-byte – character string with scanf h s or S Single-byte – character string with wscanf h s or S Wide-character string with scanf l s or S Wide-character string with wscanf l s or S Following are examples of the use of h and l with scanffunctions and wscanf functions: scanf( "%ls", &x ); // Read a wide-character string wscanf( "%lC", &x ); // Read a single-byte character To read strings not delimited by space characters, a set of characters in brackets ([ ]) can be substituted for the s (string) type character. The corresponding input field is read up to the first character that does not appear in the bracketed character set. If the first character in the set is a caret (^), the effect is reversed: The input field is read up to the first character that does appear in the rest of the character set. Note that %[a-z] and %[z-a] are interpreted as equivalent to %[abcde...z]. This is a common scanf function extension, but note that the ANSI standard does not require it. To store a string without storing a terminating null character ('\0'), use the specification %nc where n is a decimal integer. In this case, the c type character indicates that the argument is a pointer to a character array. The next n characters are read from the input stream into the specified location, and no null character ('\0') is appended. If n is not specified, its default value is 1. The scanf function scans each input field, character by character. It may stop reading a particular input field before it reaches a space character for a variety of reasons: The specified width has been reached. The next character cannot be converted as specified. The next character conflicts with a character in the control string that it is supposed to match. The next character fails to appear in a given character set. For whatever reason, when the scanf function stops reading an input field, the next input field is considered to begin at the first unread character. The conflicting character, if there is one, is considered unread and is the first character of the next input field or the first character in subsequent read operations on stdin.