fopen问题，求教高手

[doc110]

fopen打开一个文件的时候，为什么其他应用程序还可以打开。
比如我程序打开了一个文件，用计事本还是可以打开这个文件，fopen的打开方式不是是独享的吗？
为什么会出现这种情况，请高手解答。

[luciferisnotsatan]

CreateFile
OpenFile
用这两个函数吧

[qq120848369]

一个文件多个进程打开当然可以，只是使用的是不同的文件表项（包括当前文件指针偏移量），但实际操作还是落在同一个文件上。

如果想多进程共同操作一个文件,建议使用O_APPEND追加写+文件锁，写之前对整个文件加锁。

文件锁只是方便一点，其他各种锁你都可以用，只要是进程间共享的锁（信号量，prc_shared互斥锁）。（看下边说明，默认追加写是原子操作，除了NFS，所以如果不是NFS，可以不用锁。）

以下摘自linux:

   Advisory locking
       F_GETLK, F_SETLK and F_SETLKW are used to acquire, release, and test for the existence of record locks (also known as file-segment or  file-region
       locks).  The third argument, lock, is a pointer to a structure that has at least the following fields (in unspecified order).

           struct flock {
               ...
               short l_type;    /* Type of lock: F_RDLCK,
                                   F_WRLCK, F_UNLCK */
               short l_whence;  /* How to interpret l_start:
                                   SEEK_SET, SEEK_CUR, SEEK_END */
               off_t l_start;   /* Starting offset for lock */
               off_t l_len;     /* Number of bytes to lock */
               pid_t l_pid;     /* PID of process blocking our lock
                                   (F_GETLK only) */
               ...
           };

       O_APPEND
              The file is opened in append mode.  Before each write(2), the file offset is positioned at the end  of  the  file,  as  if  with  lseek(2).
              O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once.  This is because NFS does
              not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.