user-0 提问: c语言 两个程序对同一个文件读写 

回复:
user: user-1
content: http://en.cppreference.com/w/c/io/fopen

user: user-2
content: _sopen, _wsopen Open a file for sharing.  int _sopen( const char *filename, int oflag, int shflag [, int pmode ] );  int _wsopen( const wchar_t *filename, int oflag, int shflag [, int pmode ] );  Routine Required Header Optional Headers Compatibility  _sopen <io.h> <fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h> Win 95, Win NT  _wsopen <io.h> or <wchar.h> <fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.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    Return Value  Each of these functions returns a file handle for the opened file. A return value of –1 indicates an error, in which case errno is set to one of the following values:  EACCES  Given path is a directory, or file is read-only, but an open-for-writing operation was attempted.  EEXIST  _O_CREAT and _O_EXCL flags were specified, but filename already exists.  EINVAL  Invalid oflag or shflag argument.  EMFILE  No more file handles available.  ENOENT  File or path not found.  Parameters  filename  Filename  oflag  Type of operations allowed  shflag  Type of sharing allowed  pmode  Permission setting  Remarks  The _sopen function opens the file specified by filename and prepares the file for shared reading or writing, as defined by oflag and shflag. _wsopen is a wide-character version of _sopen; the filename argument to _wsopen is a wide-character string. _wsopen and _sopen behave identically otherwise.  Generic-Text Routine Mappings  TCHAR.H Routine  _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined  _tsopen _sopen _sopen _wsopen    The integer expression oflag is formed by combining one or more of the following manifest constants, defined in the file FCNTL.H. When two or more constants form the argument oflag, they are combined with the bitwise-OR operator ( | ).  _O_APPEND  Repositions file pointer to end of file before every write operation.  _O_BINARY  Opens file in binary (untranslated) mode. (See fopen for a description of binary mode.)  _O_CREAT  Creates and opens new file for writing. Has no effect if file specified by filename exists. The pmode argument is required when _O_CREAT is specified.  _O_CREAT | _O_SHORT_LIVED  Create file as temporary and if possible do not flush to disk. The pmode argument is required when _O_CREAT is specified.  _O_CREAT | _O_TEMPORARY  Create file as temporary; file is deleted when last file handle is closed. The pmode argument is required when _O_CREAT is specified.   _O_CREAT | _O_EXCL  Returns error value if file specified by filename exists. Applies only when used with _O_CREAT.  _O_NOINHERIT  Prevents creation of a shared file handle.  _O_RANDOM  Specifies primarily random access from disk.  _O_RDONLY  Opens file for reading only; cannot be specified with _O_RDWR or _O_WRONLY.  _O_RDWR  Opens file for both reading and writing; cannot be specified with _O_RDONLY or _O_WRONLY.  _O_SEQUENTIAL  Specifies primarily sequential access from disk  _O_TEXT  Opens file in text (translated) mode. (For more information, see Text and Binary Mode File I/O and fopen.)  _O_TRUNC  Opens file and truncates it to zero length; the file must have write permission. You cannot specify this flag with _O_RDONLY. _O_TRUNC used with _O_CREAT opens an existing file or creates a new file.  Warning   The _O_TRUNC flag destroys the contents of the specified file.  _O_WRONLY  Opens file for writing only; cannot be specified with _O_RDONLY or _O_RDWR.  To specify the file access mode, you must specify either _O_RDONLY, _O_RDWR, or _O_WRONLY. There is no default value for the access mode.  The argument shflag is a constant expression consisting of one of the following manifest constants, defined in SHARE.H.  _SH_DENYRW  Denies read and write access to file  _SH_DENYWR  Denies write access to file  _SH_DENYRD  Denies read access to file  _SH_DENYNO  Permits read and write access  The pmode argument is required only when you specify _O_CREAT. If the file does not exist, pmode specifies the file’s permission settings, which are set when the new file is closed the first time. Otherwise pmode is ignored. pmode is an integer expression that contains one or both of the manifest constants _S_IWRITE and _S_IREAD, defined in SYS\STAT.H. When both constants are given, they are combined with the bitwise-OR operator. The meaning of pmode is as follows:  _S_IWRITE  Writing permitted  _S_IREAD  Reading permitted  _S_IREAD | _S_IWRITE  Reading and writing permitted  If write permission is not given, the file is read-only. Under Windows NT and Windows 95, all files are readable; it is not possible to give write-only permission. Thus the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.  _sopen applies the current file-permission mask to pmode before setting the permissions (see _umask).  Example  /* LOCKING.C: This program opens a file with sharing. It locks  * some bytes before reading them, then unlocks them. Note that the  * program works correctly only if the file exists.  */  #include <io.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/locking.h> #include <share.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h>  void main( void ) {    int  fh, numread;    char buffer[40];     /* Quit if can't open file or system doesn't      * support sharing.      */    fh = _sopen( "locking.c", _O_RDWR, _SH_DENYNO,                   _S_IREAD | _S_IWRITE );    if( fh == -1 )       exit( 1 );     /* Lock some bytes and read them. Then unlock. */    if( _locking( fh, LK_NBLCK, 30L ) != -1 )    {       printf( "No one can change these bytes while I'm reading them\n" );       numread = _read( fh, buffer, 30 );       printf( "%d bytes read: %.30s\n", numread, buffer );       lseek( fh, 0L, SEEK_SET );      _locking( fh, LK_UNLCK, 30L );       printf( "Now I'm done. Do what you will with them\n" );    }    else       perror( "Locking failed\n" );     _close( fh ); }   Output  No one can change these bytes while I'm reading them 30 bytes read: /* LOCKING.C: This program ope Now I'm done. Do what you will with them   Low-level I/O Routines  See Also   _close, _creat, fopen, _fsopen, _open           _locking Locks or unlocks bytes of a file.  int _locking( int handle, int mode, long nbytes );  Routine Required Header Optional Headers Compatibility  _locking <io.h> and <sys/locking.h> <errno.h> Win 95, 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    Return Value  _locking returns 0 if successful. A return value of –1 indicates failure, in which case errno is set to one of the following values:  EACCES  Locking violation (file already locked or unlocked).  EBADF  Invalid file handle.  EDEADLOCK  Locking violation. Returned when the _LK_LOCK or _LK_RLCK flag is specified and the file cannot be locked after 10 attempts.  EINVAL  An invalid argument was given to _locking.  Parameters  handle  File handle  mode  Locking action to perform  nbytes  Number of bytes to lock  Remarks  The _locking function locks or unlocks nbytes bytes of the file specified by handle. Locking bytes in a file prevents access to those bytes by other processes. All locking or unlocking begins at the current position of the file pointer and proceeds for the next nbytes bytes. It is possible to lock bytes past end of file.  mode must be one of the following manifest constants, which are defined in LOCKING.H:  _LK_LOCK  Locks the specified bytes. If the bytes cannot be locked, the program immediately tries again after 1 second. If, after 10 attempts, the bytes cannot be locked, the constant returns an error.  _LK_NBLCK  Locks the specified bytes. If the bytes cannot be locked, the constant returns an error.  _LK_NBRLCK  Same as _LK_NBLCK.  _LK_RLCK  Same as _LK_LOCK.  _LK_UNLCK  Unlocks the specified bytes, which must have been previously locked.  Multiple regions of a file that do not overlap can be locked. A region being unlocked must have been previously locked. _locking does not merge adjacent regions; if two locked regions are adjacent, each region must be unlocked separately. Regions should be locked only briefly and should be unlocked before closing a file or exiting the program.  Example  /* LOCKING.C: This program opens a file with sharing. It locks  * some bytes before reading them, then unlocks them. Note that the  * program works correctly only if the file exists.  */  #include <io.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/locking.h> #include <share.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h>  void main( void ) {    int  fh, numread;    char buffer[40];     /* Quit if can't open file or system doesn't      * support sharing.      */    fh = _sopen( "locking.c", _O_RDWR, _SH_DENYNO,                   _S_IREAD | _S_IWRITE );    if( fh == -1 )       exit( 1 );     /* Lock some bytes and read them. Then unlock. */    if( _locking( fh, LK_NBLCK, 30L ) != -1 )    {       printf( "No one can change these bytes while I'm reading them\n" );       numread = _read( fh, buffer, 30 );       printf( "%d bytes read: %.30s\n", numread, buffer );       lseek( fh, 0L, SEEK_SET );      _locking( fh, LK_UNLCK, 30L );       printf( "Now I'm done. Do what you will with them\n" );    }    else       perror( "Locking failed\n" );     _close( fh ); }   Output  No one can change these bytes while I'm reading them 30 bytes read: /* LOCKING.C: This program ope Now I'm done. Do what you will with them   File Handling Routines  See Also   _creat, _open

user: user-3
content: 引用 5 楼 rtkgy 的回复:[quote=引用 3 楼 q3733353520 的回复:] 你这个是多线程，还是真正2个程序？ 真正的两个程序  不是多线程 [/quote]  那就是进程间通讯咯

user: user-0
content: 引用 4 楼 cfjtaishan 的回复:[quote=引用 2 楼 rtkgy 的回复:] [quote=引用 1 楼 cfjtaishan 的回复:] 程序1写入的时候写的内容还在内存里，不在文件里，所以程序2读不到内容； 当文件关闭或程序退出时，内存的数据才会刷到（磁盘或flash）文件里，还有可以通过每次强制刷到文件里。  如果是两个程序需要通讯，建议走进程间通信，当然这个需要运用进程间通信的知识，需要注意一个同步。 1.程序写入完会执行fflush 写入进去的 2.这样的情况需要进程通信吗，做到俩个互不干扰就行[/quote] 你的程序都是写吗?[/quote]  程序2 是先读一下在写 先fopen（r+）把里面内容读出来 内容会处理一下  然后fclose 在fopen(w+)清空一下 在把处理的内容写回去 就是这么个流程  也需要程序2执行的时候 程序1 不在执行

user: user-0
content: 引用 3 楼 q3733353520 的回复:你这个是多线程，还是真正2个程序？ 真正的两个程序  不是多线程

user: user-4
content: 引用 2 楼 rtkgy 的回复:[quote=引用 1 楼 cfjtaishan 的回复:] 程序1写入的时候写的内容还在内存里，不在文件里，所以程序2读不到内容； 当文件关闭或程序退出时，内存的数据才会刷到（磁盘或flash）文件里，还有可以通过每次强制刷到文件里。  如果是两个程序需要通讯，建议走进程间通信，当然这个需要运用进程间通信的知识，需要注意一个同步。 1.程序写入完会执行fflush 写入进去的 2.这样的情况需要进程通信吗，做到俩个互不干扰就行[/quote] 你的程序都是写吗?

user: user-3
content: 你这个是多线程，还是真正2个程序？

user: user-0
content: 引用 1 楼 cfjtaishan 的回复:程序1写入的时候写的内容还在内存里，不在文件里，所以程序2读不到内容； 当文件关闭或程序退出时，内存的数据才会刷到（磁盘或flash）文件里，还有可以通过每次强制刷到文件里。  如果是两个程序需要通讯，建议走进程间通信，当然这个需要运用进程间通信的知识，需要注意一个同步。 1.程序写入完会执行fflush 写入进去的 2.这样的情况需要进程通信吗，做到俩个互不干扰就行

user: user-4
content: 程序1写入的时候写的内容还在内存里，不在文件里，所以程序2读不到内容； 当文件关闭或程序退出时，内存的数据才会刷到（磁盘或flash）文件里，还有可以通过每次强制刷到文件里。  如果是两个程序需要通讯，建议走进程间通信，当然这个需要运用进程间通信的知识，需要注意一个同步。

user: user-0
content: 引用 7 楼 q3733353520 的回复:[quote=引用 5 楼 rtkgy 的回复:] [quote=引用 3 楼 q3733353520 的回复:] 你这个是多线程，还是真正2个程序？ 真正的两个程序  不是多线程 [/quote]  那就是进程间通讯咯[/quote]  看错了   两个不同的程序调用的同一个so库 去对这一个文件写入........