為什么這兩個說法不一樣啊？
uj5u.com熱心網友回復：
當然英文是對的, 拿不準看標準 https://pubs.opengroup.org/onlinepubs/9699919799/toc.htmuj5u.com熱心網友回復：
有可能有幾個原因1. 作者筆誤
2. 成文所參考的API版本不同
最簡單的方法，就是 man fopen
uj5u.com熱心網友回復：
不要迷信書、考題、老師、回帖；要迷信CPU、編譯器、除錯器、運行結果。
并請結合“盲人摸太陽”和“駕船出海時一定只帶一個指南針。”加以理解。
任何理論、權威、傳說、真理、標準、解釋、想象、知識……都比不上擺在眼前的事實！
uj5u.com熱心網友回復：
fopen, _wfopenOpen 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
uj5u.com熱心網友回復：
根據我的經驗a是可以創建的uj5u.com熱心網友回復：
看書是第一步你不能止步在第一步然后什么都不做
寫代碼試試就全明白了
uj5u.com熱心網友回復：
我覺得應該增加一個寫法，比如我又想自動創建新檔案，又想不清除原檔案內容，又不想只是追加在后面，就比較麻煩
uj5u.com熱心網友回復：
最終建議樓主寫個程式驗證一下就知道了。uj5u.com熱心網友回復：
好的好的謝謝
uj5u.com熱心網友回復：
好的 謝謝趙老師
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