Exception handling syntax: Difference between revisions

Revision as of 08:48, 10 June 2022

Revision as of 10:46, 28 June 2022

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=== Ada ===

{{Further information|Ada (programming language)}}

{{Wikibooks|Ada Programming|Exceptions}}

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=== Assembly language ===

{{Further information|Assembly language}}

Most assembly languages will have a macro instruction or an interrupt address available for the particular system to intercept events such as illegal op codes, program check, data errors, overflow, divide by zero, and other such. IBM and Univac mainframes had the [[STXIT]] macro. Digital Equipment Corporation [[RT11]] systems had trap vectors for program errors, i/o interrupts, and such. [[DOS]] has certain interrupt addresses. [[Microsoft Windows]] has specific module calls to trap program errors.

=== Bash ===

{{Further information|Bash (Unix shell)}}

<syntaxhighlight lang="bash">

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=== BASIC ===

{{Further information|BASIC}}

An ''On Error goto/gosub'' structure is used in BASIC and is quite different from modern exception handling; in BASIC there is only one global handler whereas in modern exception handling, exception handlers are stacked.

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=== C ===

{{Further information|C (programming language)}}

C does not provide direct support to exception handling: it is the programmer's responsibility to prevent errors in the first place and test return values from the functions.

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==== Microsoft-specific ====

{{Further information|Microsoft-specific exception handling mechanisms}}

Two types exist:

* Structured Exception Handling (SEH)

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=== C# ===

{{Further information|C Sharp (programming language)}}

A <code>try</code> block must have at least one <code>catch</code> or <code>finally</code> clause and at most one <code>finally</code> clause.

<syntaxhighlight lang="csharp">

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=== C++ ===

{{Further information|C++}}

<syntaxhighlight lang="cpp">

#include <exception>

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=== ColdFusion Markup Language (CFML) ===

{{Further information|ColdFusion Markup Language}}

==== Script syntax ====

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==== Railo-Lucee specific syntax ====

{{Further information|Railo|Lucee}}

Added to the standard syntax above, CFML dialects of [[Railo]] and [[Lucee]] allow a <code>retry</code> statement.<ref>https://issues.jboss.org/browse/RAILO-2176 # JBoss Community issue tracker ticket for adding <code>retry</code></ref>

This statement returns processing to the start of the prior <code>try</code> block.

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<syntaxhighlight lang="javascript">

try {

// code which could result in an exception

} catch (any e){

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=== D ===

{{Further information|D (programming language)}}

<syntaxhighlight lang="d">

import std.stdio; // for writefln()

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=== Delphi ===

{{Further information|Delphi (programming language)}}

; Exception declarations

<syntaxhighlight lang="delphi">

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raise Exception.Create('Message');

raise Exception.CreateFmt('Message with values: %d, %d',[value1, value2]); // See SysUtils.Format() for parameters.

raise ECustom.CreateCustom(X);

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=== Erlang ===

{{Further information|Erlang (programming language)}}

<syntaxhighlight lang="erlang">

try

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=== F# ===

{{Further information|F_Sharp_(programming_language)}}

In addition to the OCaml-based <code>try...with</code>, F# also has the separate <code>try...finally</code> construct, which has the same behavior as a try block with a <code>finally</code> clause in other .NET languages.

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=== Haskell ===

{{Further information|Haskell (programming language)}}

Haskell does not have special syntax for exceptions. Instead, a {{Haskell|try}}/{{Haskell|catch}}/{{Haskell|finally}}/{{Haskell|etc}}. interface is provided by functions.

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=== Java ===

{{Further information|Java (programming language)}}

{{Wikibooks|Java Programming|Exceptions}}

A <code>try</code> block must have at least one <code>catch</code> or <code>finally</code> clause and at most one <code>finally</code> clause.

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=== JavaScript ===

{{Further information|JavaScript}}

The design of JavaScript makes loud/hard errors very uncommon. [[Soft_errorSoft error|Soft/quiet errors]] are much more prevalent. Hard errors propagate to the nearest <code>try</code> statement, which must be followed by either a single <code>catch</code> clause, a single <code>finally</code> clause, or both.

<syntaxhighlight lang="javascript">

try {

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=== Lisp ===

{{Further information|Lisp (programming language)}}

==== Common Lisp ====

{{Further information|Common Lisp}}

<syntaxhighlight lang="lisp">

(ignore-errors (/ 1 0))

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=== Lua ===

{{Further information|Lua (programming language)}}

Lua uses the <code>pcall</code> and <code>xpcall</code> functions, with <code>xpcall</code> taking a function to act as a <code>catch</code> block.

; Predefined function

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=== Next Generation Shell ===

{{Further information|Next Generation Shell}}

; Defining custom exception type

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=== Objective-C ===

{{Further information|Objective-C}}

; Exception declarations

<syntaxhighlight lang="objc">

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=== OCaml ===

{{Further information|OCaml}}

<syntaxhighlight lang="ocaml">

exception MyException of string * int (* exceptions can carry a value *)

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=== Perl 5===

{{Further information|Perl}}

The [[Perl]] mechanism for exception handling uses {{Perl2|die}} to throw an exception when wrapped inside an {{Perl2|eval { ... };}} block. After the {{Perl2|eval}}, the special variable {{Perl2|$@}} contains the value passed from {{Perl2|die}}.

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The forms shown above can sometimes fail if the global variable {{Perl2|$@}} is changed between when the exception is thrown and when it is checked in the {{Perl2|if ($@)}} statement. This can happen in multi-threaded environments, or even in single-threaded environments when other code (typically

called in the destruction of some object) resets the global variable before the checking code.

The following example shows a way to avoid this problem (see [http://www.perlfoundation.org/perl5/index.cgi?exception_handling]{{deadlinkdead link|date=October 2020}} or [https://stackoverflow.com/a/10343025]; ''cf''. [http://mvp.kablamo.org/essentials/die-eval/]). But at the cost of not being able to use return values:

<syntaxhighlight lang="perl">

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=== PHP ===

{{Further information|PHP}}

<syntaxhighlight lang="php">

// Exception handling is only available in PHP versions 5 and greater.

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=== PowerBuilder ===

{{Further information|PowerBuilder}}

Exception handling is available in PowerBuilder versions 8.0 and above.

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=== PowerShell ===

{{Further information|PowerShell}}

==== Version 1.0 ====

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=== Python ===

{{Further information|Python (programming language)}}

<syntaxhighlight lang="python">

f = None

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=== R ===

{{Further information|R (programming language)}}

<syntaxhighlight lang="splus">

tryCatch({

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=== Rebol ===

{{Further information|Rebol}}

<syntaxhighlight lang="rebol">

REBOL [

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=== Rexx ===

{{Further information|Rexx}}

<syntaxhighlight lang="rexx">

signal on halt;

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=== Ruby ===

{{Further information|Ruby (programming language)}}

<syntaxhighlight lang="ruby">

begin

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=== S-Lang ===

{{Further information|S-Lang (programming library)}}

try

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=== Smalltalk ===

{{Further information|Smalltalk}}

<syntaxhighlight lang="smalltalk">

[ "code that might throw an exception" ]

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=== Swift ===

{{Further information|Swift (programming language)}}

Exception handling is supported since Swift 2.

<syntaxhighlight lang="swift">

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=== Tcl ===

{{Further information|Tcl}}

<syntaxhighlight lang="tcl">

if { [ catch {

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=== VBScript ===

{{Further information|VBScript}}

<syntaxhighlight lang="vbnet">

With New Try: On Error Resume Next

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=== Visual Basic 6 ===

{{Further information|Visual Basic}}

Exception handling syntax is very similar to Basic. Error handling is local on each procedure.

<syntaxhighlight lang="vbnet">

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==== Visual Basic .NET ====

{{Further information|Visual Basic .NET}}

A <code>Try</code> block must have at least one clause <code>Catch</code> or <code>Finally</code> clause and at most one <code>Finally</code> clause.

<syntaxhighlight lang="vbnet">

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=== Visual Prolog ===

{{Further information|Visual Prolog}}

<syntaxhighlight lang="prolog">

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=== X++ ===

{{Further information|Microsoft Dynamics AX}}

<syntaxhighlight lang="java">

public static void Main(Args _args)