C语言文件使用方式

soundbean 2021-02-05 04:00:59
为什么这两个说法不一样啊?
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希望对你有帮助:https://blog.csdn.net/it_xiangqiang/category_10581430.html 希望对你有帮助:https://blog.csdn.net/it_xiangqiang/category_10768339.html
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CodeAllen2022 2021-02-18
简单的方法是直接试试
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快乐胖电工 2021-02-16
学习了,会者不难,难者不会。好复杂
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自己敲代码实践一下就知道了
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soundbean 2021-02-05
引用 3 楼 赵4老师的回复:
不要迷信书、考题、老师、回帖; 要迷信CPU、编译器、调试器、运行结果。 并请结合“盲人摸太阳”和“驾船出海时一定只带一个指南针。”加以理解。 任何理论、权威、传说、真理、标准、解释、想象、知识……都比不上摆在眼前的事实!
好的 谢谢赵老师
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soundbean 2021-02-05
引用 6 楼 lin5161678的回复:
看书是第一步 你不能止步在第一步然后什么都不做 写代码试试就全明白了
好的好的谢谢
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自信男孩 2021-02-05
最终建议楼主写个程序验证一下就知道了。
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xian0-666 2021-02-05
我觉得应该增加一个写法,比如我又想自动创建新文件,又想不清除原文件内容,又不想只是追加在后面,就比较麻烦
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lin5161678 2021-02-05
看书是第一步 你不能止步在第一步然后什么都不做 写代码试试就全明白了
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xian0-666 2021-02-05
根据我的经验a是可以创建的
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赵4老师 2021-02-05
fopen, _wfopen Open a file. FILE *fopen( const char *filename, const char *mode ); FILE *_wfopen( const wchar_t *filename, const wchar_t *mode ); Function Required Header Compatibility fopen <stdio.h> ANSI, Win 95, Win NT _wfopen <stdio.h> or <wchar.h> Win NT For additional compatibility information, see Compatibility in the Introduction. Libraries LIBC.LIB Single thread static library, retail version LIBCMT.LIB Multithread static library, retail version MSVCRT.LIB Import library for MSVCRT.DLL, retail version The c, n, and t mode options are Microsoft extensions for fopen and _fdopen and should not be used where ANSI portability is desired. Return Value Each of these functions returns a pointer to the open file. A null pointer value indicates an error. Parameters filename Filename mode Type of access permitted Remarks The fopen function opens the file specified by filename. _wfopen is a wide-character version of fopen; the arguments to _wfopen are wide-character strings. _wfopen and fopen behave identically otherwise. Generic-Text Routine Mappings TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined _tfopen fopen fopen _wfopen The character string mode specifies the type of access requested for the file, as follows: "r" Opens for reading. If the file does not exist or cannot be found, the fopen call fails. "w" Opens an empty file for writing. If the given file exists, its contents are destroyed. "a" Opens for writing at the end of the file (appending) without removing the EOF marker before writing new data to the file; creates the file first if it doesn’t exist. "r+" Opens for both reading and writing. (The file must exist.) "w+" Opens an empty file for both reading and writing. If the given file exists, its contents are destroyed. "a+" Opens for reading and appending; the appending operation includes the removal of the EOF marker before new data is written to the file and the EOF marker is restored after writing is complete; creates the file first if it doesn’t exist. When a file is opened with the "a" or "a+" access type, all write operations occur at the end of the file. The file pointer can be repositioned using fseek or rewind, but is always moved back to the end of the file before any write operation is carried out. Thus, existing data cannot be overwritten. The "a" mode does not remove the EOF marker before appending to the file. After appending has occurred, the MS-DOS TYPE command only shows data up to the original EOF marker and not any data appended to the file. The "a+" mode does remove the EOF marker before appending to the file. After appending, the MS-DOS TYPE command shows all data in the file. The "a+" mode is required for appending to a stream file that is terminated with the CTRL+Z EOF marker. When the "r+", "w+", or "a+" access type is specified, both reading and writing are allowed (the file is said to be open for “update”). However, when you switch between reading and writing, there must be an intervening fflush, fsetpos, fseek, or rewind operation. The current position can be specified for the fsetpos or fseek operation, if desired. In addition to the above values, the following characters can be included in mode to specify the translation mode for newline characters: t Open in text (translated) mode. In this mode, CTRL+Z is interpreted as an end-of-file character on input. In files opened for reading/writing with "a+", fopen checks for a CTRL+Z at the end of the file and removes it, if possible. This is done because using fseek and ftell to move within a file that ends with a CTRL+Z, may cause fseek to behave improperly near the end of the file. Also, in text mode, carriage return–linefeed combinations are translated into single linefeeds on input, and linefeed characters are translated to carriage return–linefeed combinations on output. When a Unicode stream-I/O function operates in text mode (the default), the source or destination stream is assumed to be a sequence of multibyte characters. Therefore, the Unicode stream-input functions convert multibyte characters to wide characters (as if by a call to the mbtowc function). For the same reason, the Unicode stream-output functions convert wide characters to multibyte characters (as if by a call to the wctomb function). b Open in binary (untranslated) mode; translations involving carriage-return and linefeed characters are suppressed. If t or b is not given in mode, the default translation mode is defined by the global variable _fmode. If t or b is prefixed to the argument, the function fails and returns NULL. For more information about using text and binary modes in Unicode and multibyte stream-I/O, see Text and Binary Mode File I/O and Unicode Stream I/O in Text and Binary Modes. c Enable the commit flag for the associated filename so that the contents of the file buffer are written directly to disk if either fflush or _flushall is called. n Reset the commit flag for the associated filename to “no-commit.” This is the default. It also overrides the global commit flag if you link your program with COMMODE.OBJ. The global commit flag default is “no-commit” unless you explicitly link your program with COMMODE.OBJ. Valid characters for the mode string used in fopen and _fdopen correspond to oflag arguments used in _open and _sopen, as follows. Characters in mode String Equivalent oflag Value for _open/_sopen a _O_WRONLY | _O_APPEND (usually _O_WRONLY | _O_CREAT | _O_APPEND) a+ _O_RDWR | _O_APPEND (usually _O_RDWR | _O_APPEND | _O_CREAT ) r _O_RDONLY r+ _O_RDWR w _O_WRONLY (usually _O_WRONLY | _O_CREAT | _O_TRUNC) w+ _O_RDWR (usually _O_RDWR | _O_CREAT | _O_TRUNC) b _O_BINARY t _O_TEXT c None n None Example /* FOPEN.C: This program opens files named "data" * and "data2".It uses fclose to close "data" and * _fcloseall to close all remaining files. */ #include <stdio.h> FILE *stream, *stream2; void main( void ) { int numclosed; /* Open for read (will fail if file "data" does not exist) */ if( (stream = fopen( "data", "r" )) == NULL ) printf( "The file 'data' was not opened\n" ); else printf( "The file 'data' was opened\n" ); /* Open for write */ if( (stream2 = fopen( "data2", "w+" )) == NULL ) printf( "The file 'data2' was not opened\n" ); else printf( "The file 'data2' was opened\n" ); /* Close stream */ if( fclose( stream ) ) printf( "The file 'data' was not closed\n" ); /* All other files are closed: */ numclosed = _fcloseall( ); printf( "Number of files closed by _fcloseall: %u\n", numclosed ); } Output The file 'data' was opened The file 'data2' was opened Number of files closed by _fcloseall: 1 Stream I/O Routines See Also fclose, _fdopen, ferror, _fileno, freopen, _open, _setmode
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赵4老师 2021-02-05
不要迷信书、考题、老师、回帖; 要迷信CPU、编译器、调试器、运行结果。 并请结合“盲人摸太阳”和“驾船出海时一定只带一个指南针。”加以理解。 任何理论、权威、传说、真理、标准、解释、想象、知识……都比不上摆在眼前的事实!
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NorZ 2021-02-05
有可能有几个原因 1. 作者笔误 2. 成文所参考的API版本不同 最简单的方法,就是 man fopen
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LubinLew 2021-02-05
当然英文是对的, 拿不准看标准 https://pubs.opengroup.org/onlinepubs/9699919799/toc.htm
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