[英]monitoring a file for changes
I'm trying to achieve tail -like functionality in my Visual Studio 2008 C++ application. 我正在尝试在Visual Studio 2008 C ++应用程序中实现类似尾部的功能。 (ie show in real-time the changes to a file not owned by my process.)
(即实时显示对我的进程不拥有的文件的更改。)
/// name of the file to tail
std::string file_name_;
/// position of the last-known end of the file
std::ios::streampos file_end_;
// start by getting the position of the end of the file.
std::ifstream file( file_name_.c_str() );
if( file.is_open() )
{
file.seekg( 0, std::ios::end );
file_end_ = file.tellg();
}
/// callback activated when the file has changed
void Tail::OnChanged()
{
// re-open the file
std::ifstream file( file_name_.c_str() );
if( file.is_open() )
{
// locate the current end of the file
file.seekg( 0, std::ios::end );
std::streampos new_end = file.tellg();
// if the file has been added to
if( new_end > file_end_ )
{
// move to the beginning of the additions
file.seekg( 0, new_end - file_end_ );
// read the additions to a character buffer
size_t added = new_end - file_end_;
std::vector< char > buffer( added + 1 );
file.read( &buffer.front(), added );
// display the additions to the user
// this is always the correct number of bytes added to the file
std::cout << "added " << added << " bytes:" << std::endl;
// this always prints nothing
std::cout << &buffer.front() << std::endl << std::endl;
}
// remember the new end of the file
file_end_ = new_end;
}
}
While it always knows how many bytes have been added to the file, the read buffer is always empty. 尽管它始终知道已向文件添加了多少字节,但读取缓冲区始终为空。 What do I need to do to get the functionality I'm after?
我需要做什么才能获得所需的功能?
Thanks, PaulH 谢谢PaulH
EDIT: nevermind. 编辑:没关系。 I got it sorted.
我把它整理好了。 I was using seekg() incorrectly.
我使用了不正确的seekg()。 This is what I should have been doing:
这是我应该做的:
if( new_end > file_end_ )
{
size_t added = new_end - file_end_;
file.seekg( -added, std::ios::end );
Thanks 谢谢
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