Sixth chapter-Document management (i) (2)

6.1.4.2 file Positioning

Seek: Move the current position of the file to the specified section

Filepos: Returns the current location of the file

Eoln: Return line End Flag

EOF: Return file End Flag

FileSeek: Change the position of the current file pointer

The difference between seek and FileSeek is: 1. Seek is used only for recording files; 2. The FileSeek parameter is the file handle, offset, and start position. Where the starting position has the first file, the current position, the end of the file three choices. The argument for seek is a file variable, an offset, and the offset is positioned from the beginning of the file. 3. The offset of the FileSeek is computed in bytes, and seek is moved according to the record number.

Seek, Filepos only for recording files. However, any file can be considered a byte-based record file. The following procedure represents their use.

{The design interface for this example is a form that contains a topendialog part.} }

Uses Dialogs;

Var

F:file of Byte;

Size:longint;

s:string;

Y:integer;

Begin

If Opendialog1.execute Then

Begin

AssignFile (f, opendialog1.filename);

Reset (f);

Size: = FileSize (f);

S: = ' File size in bytes: ' + inttostr (size);

Y: = 10;

Canvas.textout (5, Y, S);

Y: = y + canvas.textheight (S) + 5;

S: = ' seeking halfway into file ... ';

Canvas.textout (5, Y, S);

Y: = y + canvas.textheight (S) + 5;

Seek (f,size Div 2);

S: = ' Position is now ' + INTTOSTR (Filepos (f));

Canvas.textout (5, Y, S);

CloseFile (f);

End

End.

6.1.4.3 file deletion and truncation

Erase: Deletes a file that exists

DeleteFile: Delete a file

Truncate: Truncate files from the current location of the file

The difference between erase and DeleteFile is that erase takes a file variable as a parameter and causes an exception when the file cannot be deleted, DeleteFile returns False when the file is not present or cannot be deleted, without causing an exception.

6.1.4.4 File name action

Rename: File Rename, file variable as action object

RenameFile: File name renamed, parameter is the original name of the file and new names

Changefileext: Changing the file name extension

Expandfilename: Return file full path name

Extractfileext: Returns the file name extension

Extractfilename: Returns the filename from the full path name

Extractfilepath: Returns the path to a specific file

6.1.4.5 file Properties

Filegetattr: Returning file properties

Filesetattr: Setting file properties

6.1.4.6 file Status

FileSize: Returns the size of the file object

IOResult: Returns the status of the last I/O operation

FileExists: Detects if a file exists

6.1.4.7 file Date

Datetimetofiledate: Convert Delphi date format to DOS date format

Filedatetodatetime: Convert the DOS date format to Delphi date format

Filegetdate: Returns a DOS date timestamp for a file

Filesetdate: Set the file's DOS date time stamp

6.1.4.8 file reading and writing

READ,READLN: Reading variables from text or record files

Write: Writes the specified variable to a text or record file

Writeln: Writes the specified variable to a text file and writes a line end flag

Fileread: Reading variables from a specified file

FileWrite: Write data to the specified file

Fileread and FileWrite are the object of the file handle, mainly for internal use of the system.

6.1.4.9 Directory Operations

MkDir: Create subdirectories of current directory

ChDir: Changing the current directory

Getdir: Returns the current directory for a specific disk

RmDir: Delete an empty directory

6.1.4.10 Disk Operations

Diskfree: Back to disk free space

DiskSize: Returns the size of a specific disk

6.1.4.11 File Lookup

FileSearch: Find out if a particular file exists in the directory

FindFirst: Finds the first file in the directory that matches the given file name (which can contain a match) and the property set

FindNext: Returns the next file that meets the criteria

FindClose: Abort a findfirst/findnext sequence

For more detailed information about the file management standard process/function, please consult the Delphi related Help topics. Most of the above processes are followed by an application, which the reader can use.

The process/function of the file is divided into two topics in Delphi's online Help assistance system: I/O routine and file_management routine. The former mostly takes the file variable as the manipulation object, while the latter mostly takes the file name or the file handle as the manipulation object. In order to facilitate the use of readers, we have reclassified by function. The following section mainly applies the process under the I/O routine theme, while in the fourth section The synthesis example mainly applies the process under the File_management routine theme.

In addition, Windows provides a number of API functions for file management. Although in general, using the functions provided by Delphi is enough to solve the problem, sometimes you still need to use the Windows API. In (6.4.4.2) we use the Windows API function GetDriveType. For information about Windows API functions, please refer to the relevant data, which is not covered here.