Delphi in a Nutshell

Name

File Keyword

Syntax

var
  BinaryFile: file;
  TypedFile: file of Some type;

Description

A file is a binary sequence of some type. A file’s contents are usually stored in a persistent medium, such as a disk drive. If you do not specify a type, the untyped file is treated as a sequence of fixed-size records where the record size is determined when you open the file with Reset or Rewrite.

Internally, Delphi represents a binary file as a record. The SysUtils unit declares the TFileRec type for your convenience, or you can declare the record yourself:

type
  TFileRec = packed record
    Handle: Integer;                 // Windows file handle
    Mode: Integer;              // fmInput, fmOutput, fmInOut, fmClosed
    RecSize: Cardinal;               // record size
    Private: array[1..28] of Byte;   // reserved by Delphi
    UserData: array[1..32] of Byte;  // you can use this
    Name: array[0..259] of Char;     // file path
  end;

Tips and Tricks

• The file type is for binary files. See the TextFile type for text files. Binary and text files often follow completely different rules in Delphi. Note also that the TextFile type is not the same as file of Char.

• The base type for a file can be a scalar type, an array type, or a record type. It should not be a pointer, dynamic array, or long string. Storing a pointer in a file serves no useful purpose because pointer values are ephemeral. Long and wide strings are pointers, so if you need to store strings in a file, use short strings or call BlockRead and BlockWrite.

• Call Reset to open an existing file or Rewrite to create ...