Difference between revisions of "&"

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(→‎octal base: add note about exemptions)
 
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{{&}}
 
{{&}}
 
<div style="float:left; margin: 0 25px 20px 0; padding:40px; font-size:500%; font-family: Georgia; background-color: #f9f9f9; border: 2px solid #777777;">&</div>
 
<div style="float:left; margin: 0 25px 20px 0; padding:40px; font-size:500%; font-family: Georgia; background-color: #f9f9f9; border: 2px solid #777777;">&</div>
In [[ASCII]] the character code decimal <syntaxhighlight lang="pascal" enclose="none">38</syntaxhighlight> (or [[Hexadecimal|<syntaxhighlight lang="pascal" enclose="none">$</syntaxhighlight>]]<syntaxhighlight lang="pascal" enclose="none">26</syntaxhighlight>) is defined to be <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight> (pronounced “ampersand”).
+
In [[ASCII]] the character code decimal <syntaxhighlight lang="pascal" inline>38</syntaxhighlight> (or [[Hexadecimal|<syntaxhighlight lang="pascal" inline>$</syntaxhighlight>]]<syntaxhighlight lang="pascal" inline>26</syntaxhighlight>) is defined to be <syntaxhighlight lang="pascal" inline>&</syntaxhighlight> (pronounced “ampersand”).
  
 
== Pascal ==
 
== Pascal ==
 
=== octal base ===
 
=== octal base ===
In [[Pascal]] the <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight> denotes an octal base number.
+
In [[Pascal]] the <syntaxhighlight lang="pascal" inline>&</syntaxhighlight> denotes an octal base number.
 
<syntaxhighlight lang="pascal" line highlight="9">
 
<syntaxhighlight lang="pascal" line highlight="9">
 
program messageNo(input, output, stderr);
 
program messageNo(input, output, stderr);
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end.
 
end.
 
</syntaxhighlight>
 
</syntaxhighlight>
In an octal base only the characters <syntaxhighlight lang="pascal" enclose="none">0</syntaxhighlight> through and including <syntaxhighlight lang="pascal" enclose="none">7</syntaxhighlight> are allowed.
+
In an octal base only the characters <syntaxhighlight lang="pascal" inline>0</syntaxhighlight> through and including <syntaxhighlight lang="pascal" inline>7</syntaxhighlight> are allowed.
An optional sign is specified in front of the <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight>.
+
An optional sign is specified in front of the <syntaxhighlight lang="pascal" inline>&</syntaxhighlight>.
  
 
As a passing remark, in a production program the number in the above example is better written as
 
As a passing remark, in a production program the number in the above example is better written as
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=== identifier escape ===
 
=== identifier escape ===
 
[[FPC|FreePascal]] retroactively declared some new [[Reserved word|reserved words]].
 
[[FPC|FreePascal]] retroactively declared some new [[Reserved word|reserved words]].
In order of being capable of compiling old code with an up-to-date [[Compiler|compiler]] version, which might fail due to those new reserved words, FPC declared the <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight> as an escape character.
+
In order of being capable of compiling old code with an up-to-date [[Compiler|compiler]] version, which might fail due to those new reserved words, FPC declared the <syntaxhighlight lang="pascal" inline>&</syntaxhighlight> as an escape character.
Thus, without refactoring the code but escaping, i.e. prepending an <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight> to the [[Identifier|identifier]], the compiler accepts the actual reserved word as a valid identifier. New code though shall come up with different identifier names, without utilizing this feature.
+
Thus, without refactoring the code but escaping, i.e. prepending an <syntaxhighlight lang="pascal" inline>&</syntaxhighlight> to the [[Identifier|identifier]], the compiler accepts the actual reserved word as a valid identifier. New code though shall come up with different identifier names, without utilizing this feature.
  
 
== Lazarus ==
 
== Lazarus ==
In [[Lazarus]] the <syntaxhighlight lang="pascal" enclose="none">&</syntaxhighlight> is used to
+
In [[Lazarus]] the <syntaxhighlight lang="pascal" inline>&</syntaxhighlight> is used to
* indicate shortcut keys in [[TMenuItem|<syntaxhighlight lang="pascal" enclose="none">TMenuItem</syntaxhighlight>]]
+
* indicate shortcut keys in [[TMenuItem|<syntaxhighlight lang="pascal" inline>TMenuItem</syntaxhighlight>]]
  
 
{{Symbols}}
 
{{Symbols}}

Latest revision as of 16:24, 6 August 2022

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&

In ASCII the character code decimal 38 (or $26) is defined to be & (pronounced “ampersand”).

Pascal

octal base

In Pascal the & denotes an octal base number.

 1program messageNo(input, output, stderr);
 2
 3uses
 4	baseUnix;
 5
 6begin
 7	// withdraw group write access to current terminal
 8	// equivalent to invoking: mesg n
 9	fpChmod('/dev/stdin', &0600);
10end.

In an octal base only the characters 0 through and including 7 are allowed. An optional sign is specified in front of the &.

As a passing remark, in a production program the number in the above example is better written as

fpChmod('/dev/stdin', S_IRUSR or S_IWUSR);

since it is more meaningful than having a raw number. Pascal is a high-level language. Use this advantage. Write what you mean, not what in fact the computer does.

Note-icon.png

Note: Octal number literals are not supported in {$mode Delphi} and {$mode TP}.

identifier escape

FreePascal retroactively declared some new reserved words. In order of being capable of compiling old code with an up-to-date compiler version, which might fail due to those new reserved words, FPC declared the & as an escape character. Thus, without refactoring the code but escaping, i.e. prepending an & to the identifier, the compiler accepts the actual reserved word as a valid identifier. New code though shall come up with different identifier names, without utilizing this feature.

Lazarus

In Lazarus the & is used to


navigation bar: topic: Pascal symbols
single characters

+ (plus)  •  - (minus)  •  * (asterisk)  •  / (slash)
= (equal)  •  > (greater than)  •  < (less than)
. (period)  •  : (colon)  •  ; (semi colon)
^ (hat)  •  @ (at)
$ (dollar sign)  •  & (ampersand)  •  # (hash)
' (single quote)

character pairs

<> (not equal)  •  <= (less than or equal)  •  := (becomes)  •  >= (greater than or equal)

 •  >< (symmetric difference)  •  // (double slash)