Quick start manual

8-2 Delphi Language Guide
File input and output
A file variable is any variable whose type is a file type. There are three classes of file:
typed, text, and untyped. The syntax for declaring file types is given in “File types” on
page 5-26.
Before a file variable can be used, it must be associated with an external file through a
call to the AssignFile procedure. An external file is typically a named disk file, but it
can also be a device, such as the keyboard or the display. The external file stores the
information written to the file or supplies the information read from the file.
Once the association with an external file is established, the file variable must be
“opened” to prepare it for input or output. An existing file can be opened via the
Reset procedure, and a new file can be created and opened via the Rewrite procedure.
Text files opened with Reset are read-only and text files opened with Rewrite and
Append are write-only. Typed files and untyped files always allow both reading and
writing regardless of whether they were opened with Reset or Rewrite.
Every file is a linear sequence of components, each of which has the component type
(or record type) of the file. The components are numbered starting with zero.
Files are normally accessed sequentially. That is, when a component is read using the
standard procedure Read or written using the standard procedure Write, the current
file position moves to the next numerically ordered file component. Typed files and
untyped files can also be accessed randomly through the standard procedure Seek,
which moves the current file position to a specified component. The standard
functions FilePos and FileSize can be used to determine the current file position and
the current file size.
Flush Flushes the buffer of an output text file.
GetDir Returns the current directory of a specified drive.
IOResult Returns an integer value that is the status of the last I/O function performed.
MkDir Creates a subdirectory.
Read Reads one or more values from a file into one or more variables.
Readln Does what Read does and then skips to beginning of next line in the text file.
Rename Renames an external file.
Reset Opens an existing file.
Rewrite Creates and opens a new file.
RmDir Removes an empty subdirectory.
Seek Moves the current position of a typed or untyped file to a specified component.
Not used with text files.
SeekEof Returns the end-of-file status of a text file.
SeekEoln Returns the end-of-line status of a text file.
SetTextBuf Assigns an I/O buffer to a text file.
Truncate Truncates a typed or untyped file at the current file position.
Write Writes one or more values to a file.
Writeln Does the same as Write, and then writes an end-of-line marker to the text file.
Table 8.1 Input and output procedures and functions (continued)
Procedure or
function Description