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分享c语言 两个程序对同一个文件读写
如题
有两个程序会同事对同一个文件读写
程序1，打开文件的方式是open（r+），这个fp 常开，有内容呢，就顺序写入，为了防止程序2改完内容，会写重复的问题，每次write操作之前都会执行一次fseek(fp, 0, SEEK_END)
程序2，打开文件方式是open（w+），一次一调用的，就是为了改改文件内的内容
疑问是
问题1：1程序在执行写入的时候，2程序是没办法执行的吧？反过来 2程序执行的时候 1程序没办法执行写入?
问题2：这种方式会出现死锁什么的问题吗？例如程序1 已经写入完了，但是程序2 依然没办法执行
有两个程序会同事对同一个文件读写
程序1，打开文件的方式是open（r+），这个fp 常开，有内容呢，就顺序写入，为了防止程序2改完内容，会写重复的问题，每次write操作之前都会执行一次fseek(fp, 0, SEEK_END)
程序2，打开文件方式是open（w+），一次一调用的，就是为了改改文件内的内容
疑问是
问题1：1程序在执行写入的时候，2程序是没办法执行的吧？反过来 2程序执行的时候 1程序没办法执行写入?
问题2：这种方式会出现死锁什么的问题吗？例如程序1 已经写入完了，但是程序2 依然没办法执行
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paschen 2017-03-29
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赵4老师 2017-03-29
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_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
我用双手-成就你的梦想 2017-03-29
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真正的两个程序 不是多线程 [/quote]
那就是进程间通讯咯
Banio 2017-03-29
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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
Banio 2017-03-29
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真正的两个程序 不是多线程
自信男孩 2017-03-29
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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?
我用双手-成就你的梦想 2017-03-29
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你这个是多线程，还是真正2个程序？
Banio 2017-03-29
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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
自信男孩 2017-03-29
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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。
Banio 2017-03-29
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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........
