C++编程中设置文件长度的方法

转自：http://blog.csdn.net/rrrfff/article/details/6705685

bool SetFileLength(const char *FilePath, off_t Length)  
{  
#ifdef WIN32  
    System::IO::FileStream *File = System::IO::File::Open(Length, File::OpenMode, File::AllAccess);  
    if (!File)  
    {  
        return false;  
    }  
    /// <summary>  
    /// 表达式调用 File->SetLength() 方法  
    /// 该方法的底层实现是调用NtSetInformationFile  
    /// 并通过 FILE_END_OF_FILE_INFORMATION 结构来设置文件长度  
    /// 该方法的优势是可以直接设置 LONGLONG 型的长度  
    /// </summary>  
    File->Length = Length;  
    delete File;  
    return true;  
    //参考资料  
    //http://msdn.microsoft.com/en-us/library/ff567096(v=VS.85).aspx  
#else  
    int fd = open(FilePath, O_RDWR);  
    /// <summary>  
    /// -1 if an error occurred  
    /// </summary>  
    if (fd == -1)  
    {  
        return false;  
    }  
    /// <summary>  
    /// On success, zero is returned. On error, -1 is returned, and errno is set appropriately.  
    /// </summary>  
    return ftruncate(fd, Length) == 0;  
    //参考资料  
    //http://api.taocpp.com/doc/path/linux系统调用/文件读写/ftruncate/  
    //http://linux.die.net/man/2/ftruncate  
#endif  
}