Difference between revisions of "Text"

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m (Fixed syntax highlighting)
 
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In this article, for the sake of ease of understanding, [[reserved word]]s in Pascal are shown in UPPER CASE even though the Pascal lanugage is not case sensitive.
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{{Text}}
  
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The term '''text''', when used in a Pascal program, is a shortcut for the [[type]] ''[[File|file]] of [[Char|char]]''. The following Pascal definitions should be equivalent:
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The type '''TextFile''' (or, equivalent and older, just '''Text''') is used in a Pascal program to read from and write to a text file.
  
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:VAR filname: FILE OF char;
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<syntaxhighlight lang=pascal>
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:VAR filname: text;
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{$mode objfpc}{$H+}
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var
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  MyFile: TextFile;
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  s: string;
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begin
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  AssignFile(MyFile, 'a.txt');
  
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In the above example, the [[Identifier|identifier]] used (''filname'') is the file [[Variable|variable]] which is used to do input, output, or both, to the actual file.  The file variable, however, is not the actual file; the file variable must be tied to the actual file  by a [[RTL|run-time library]] routine.  In most cases, this is done via the [[assign]] procedure followed by use of the [[reset]] or [[rewrite]] procedure.  In the case of specialized files such as databases, it is done via some other method than the standard ones, in order to allow a file variable to actually read from and/or write to the actual [[File|file]] itself using specialized routines.
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  try
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    reset(MyFile);    //Reopen the file for reading
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    readln(MyFile, s);
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    writeln('Text read from file: ', s)
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    {
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    or add some text:
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    append(MyFile);
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    writeln(MyFile, 'some text');
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    }
  
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<HR>
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  finally
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When the term '''Text''' is used for [[File|files]] in general, it refers to a type of file which consists of ordinary information which is (usually) readable by a person. This includes documents, [[Source code|source code]] of Pascal Programs, web pages, and other such items. This differs from a [[Binary|binary]] file, which is generally not human readable, and is used to store machine-readable data.
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    CloseFile(MyFile)
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  end
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end.</syntaxhighlight>
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The [[Variable|variable]] representing the text file (''MyFile'' in the example above) may be used to read from, write to, or both to the actual file. It must be tied to the actual file by a [[RTL|run-time library]] routine [[AssignFile]]. Then the file must be opened by the [[Reset]], [[Rewrite]] or [[Append]] procedure. You can read and write to file using Read, Readln, Write, Writeln. After you have finished processing the file, you should release the necessary file resources by closing the file calling [[CloseFile]].
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Note that '''TextFile''' type is very different than the '''file of char''' type:
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* '''file of char''' is just a simple sequence of single byte characters and you can only read or write a single character at a time. That is, you can only call '''Read(F, C)''' or '''Write(F, C)''' where C is variable of type '''char'''.
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* '''TextFile''' offers much more functions, and represents the usual concept of a text file. You can use Read, Readln, Write, Writeln to read/write from a text file a number of standard types, like strings, integers and floating-point values. [[End_of_Line|Line endings]] are also automatically handled: when reading, various line endings are recognized; when writing, the current OS line endings are used.
  
 
{{File}}
 
{{File}}

Latest revision as of 10:14, 29 February 2020

│ English (en) │ 日本語 (ja) │ русский (ru) │

The type TextFile (or, equivalent and older, just Text) is used in a Pascal program to read from and write to a text file. 

{$mode objfpc}{$H+}
var 
  MyFile: TextFile;
  s: string;
begin
  AssignFile(MyFile, 'a.txt');

  try
    reset(MyFile);    //Reopen the file for reading
    readln(MyFile, s);
    writeln('Text read from file: ', s) 
   
    {
    or add some text:
    append(MyFile);
    writeln(MyFile, 'some text'); 
    }

  finally
    CloseFile(MyFile)
  end
end.

The variable representing the text file (MyFile in the example above) may be used to read from, write to, or both to the actual file. It must be tied to the actual file by a run-time library routine AssignFile. Then the file must be opened by the Reset, Rewrite or Append procedure. You can read and write to file using Read, Readln, Write, Writeln. After you have finished processing the file, you should release the necessary file resources by closing the file calling CloseFile.

Note that TextFile type is very different than the file of char type:

  • file of char is just a simple sequence of single byte characters and you can only read or write a single character at a time. That is, you can only call Read(F, C) or Write(F, C) where C is variable of type char.
  • TextFile offers much more functions, and represents the usual concept of a text file. You can use Read, Readln, Write, Writeln to read/write from a text file a number of standard types, like strings, integers and floating-point values. Line endings are also automatically handled: when reading, various line endings are recognized; when writing, the current OS line endings are used.

File-related types, procedures and functions:

File - Text - AssignFile - CloseFile - Reset - Rewrite - Get - Put - Read - Readln - Write - Writeln
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