_lock_file

 

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

Locks a FILE object to ensure consistency for threads accessing the FILE object concurrently.

void _lock_file(  
   FILE* file  
);  

Parameters

file
File handle.

The _lock_file function locks the FILE object specified by file. The underlying file is not locked by _lock_file. Use _unlock_file to release the lock on the file. Calls to _lock_file and _unlock_file must be matched in a thread.

RoutineRequired header
_lock_file<stdio.h>

For more compatibility information, see Compatibility in the Introduction.

// crt_lock_file.c  
// This example creates multiple threads that write to standard output  
// concurrently, first with _file_lock, then without.  
  
#include <stdio.h>  
#include <process.h>// _beginthread  
#include <windows.h>// HANDLE  
  
void Task_locked( void* str )  
{  
    for( int i=0; i<1000; ++i )  
    {  
        _lock_file( stdout );  
        for( char* cp = (char*)str; *cp; ++cp )  
        {  
            _fputc_nolock( *cp, stdout );  
        }  
        _unlock_file( stdout );  
    }  
}  
  
void Task_unlocked( void* str )  
{  
    for( int i=0; i<1000; ++i )  
    {  
        for( char* cp = (char*)str; *cp; ++cp )  
        {  
            fputc( *cp, stdout );  
        }  
    }  
}  
  
int main()  
{  
    HANDLE h[3];  
    h[0] = (HANDLE)_beginthread( &Task_locked, 0, "First\n" );  
    h[1] = (HANDLE)_beginthread( &Task_locked, 0, "Second\n" );  
    h[2] = (HANDLE)_beginthread( &Task_locked, 0, "Third\n" );  
  
    WaitForMultipleObjects( 3, h, true, INFINITE );  
  
    h[0] = (HANDLE)_beginthread( &Task_unlocked, 0, "First\n" );  
    h[1] = (HANDLE)_beginthread( &Task_unlocked, 0, "Second\n" );  
    h[2] = (HANDLE)_beginthread( &Task_unlocked, 0, "Third\n" );  
  
    WaitForMultipleObjects( 3, h, true, INFINITE );  
}  

...  
First  
Second  
First  
Second  
Third  
Second  
Third  
Second  
...  
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System::IO::FileStream::Lock

File Handling
_creat, _wcreat
_open, _wopen
_unlock_file

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