Difference between revisions of "runtime error"
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{{runtime error}} | {{runtime error}} | ||
| + | A run-time error is an irreparable error condition that arises during the [[runtime|run-time]], i.e. the execution of a [[Executable program|program]]. | ||
| − | A | + | == Behavior == |
| + | The [[FPC]] inserts code to detect a vast number of error situations. | ||
| + | If such a situation is encountered, the standard [[RTL|run-time library]] will initiate the termination of the program. | ||
| + | A run-time error number, and the address the error occurred at is being printed. | ||
| + | This is the safest and cheapest error treatment. | ||
| + | |||
| + | == Comparative remarks == | ||
| + | |||
| + | === Compile-time errors === | ||
| + | |||
| + | In contrast to [[compile-time error|compile-time errors]], which the compiler detects during [[Compile time|compilation]], run-time errors depend on the state of the program, thus can not be foreseen in advance. | ||
| + | If a compile-time error is encountered, no executable program is generated. | ||
| + | |||
| + | === Exceptions === | ||
| + | |||
| + | Run-time errors are the classical imperative approach in order to avoid inconsistent program states, which may eventually cause faulty program behavior. | ||
| + | If FPC's {{Doc|package=RTL|unit=sysutils|text=<syntaxhighlight lang="pascal" inline>sysUtils</syntaxhighlight> unit}} is included, all run-time errors become [[Exceptions|exceptions]] (cf. {{Doc|package=RTL|unit=system|identifier=runtimeerrors|text=<syntaxhighlight lang="pascal" inline>system.runTimeErrors</syntaxhighlight>}} for details). | ||
| + | Unlike run-time errors those can be caught by [[Try|<syntaxhighlight lang="pascal" inline>try</syntaxhighlight>]]...[[Except| <syntaxhighlight lang="pascal" inline>except</syntaxhighlight>]] | ||
| + | [[On|<syntaxhighlight lang="pascal" inline>on</syntaxhighlight>]]...[[Do|<syntaxhighlight lang="pascal" inline>do</syntaxhighlight>]] ... [[End|<syntaxhighlight lang="pascal" inline>end</syntaxhighlight>]] [[Block|blocks]], provided a mode allowing exceptions – such as [[Mode ObjFPC|<syntaxhighlight lang="pascal" inline>{$mode ObjFPC}</syntaxhighlight>]] or [[Mode Delphi|<syntaxhighlight lang="pascal" inline>{$mode Delphi}</syntaxhighlight>]] – is being used. | ||
| + | A run-time error causes the program to terminate, while an exception may give the opportunity to “fix” the problem. | ||
| + | This standard behavior of {{Doc|package=RTL|unit=system|identifier=runerror|text=<syntaxhighlight lang="pascal" inline>system.runError</syntaxhighlight>}} can be altered by assigning a non-[[Nil|<syntaxhighlight lang="pascal" inline>nil</syntaxhighlight>]] value to {{Doc|package=RTL|unit=system|identifier=errorproc|text=<syntaxhighlight lang="pascal" inline>system.errorProc</syntaxhighlight>}}. | ||
== See also == | == See also == | ||
| − | + | * [https://www.freepascal.org/docs-html/user/userap4.html Appendix D in the Free Pascal User's Guide: “Run-time errors”] | |
| − | * [https://www.freepascal.org/docs-html/user/userap4.html | + | * [[RunError|procedure <syntaxhighlight lang="pascal" inline>runError</syntaxhighlight>]] |
| − | * | + | * [https://www.freepascal.org/docs-html/current/user/userse58.html “Line numbers in run-time error backtraces”] in the Free Pascal User's Guide |
| − | + | * {{Doc|package=RTL|unit=system|identifier=returnnilifgrowheapfails|text=<syntaxhighlight lang="pascal" inline>system.returnNilIfGrowHeapFails</syntaxhighlight>}} | |
| − | |||
| − | * [https://www.freepascal.org/docs-html/current/user/userse58.html | ||
Latest revision as of 17:14, 6 August 2022
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A run-time error is an irreparable error condition that arises during the run-time, i.e. the execution of a program.
Behavior
The FPC inserts code to detect a vast number of error situations. If such a situation is encountered, the standard run-time library will initiate the termination of the program. A run-time error number, and the address the error occurred at is being printed. This is the safest and cheapest error treatment.
Comparative remarks
Compile-time errors
In contrast to compile-time errors, which the compiler detects during compilation, run-time errors depend on the state of the program, thus can not be foreseen in advance. If a compile-time error is encountered, no executable program is generated.
Exceptions
Run-time errors are the classical imperative approach in order to avoid inconsistent program states, which may eventually cause faulty program behavior.
If FPC's sysUtils unit is included, all run-time errors become exceptions (cf. system.runTimeErrors for details).
Unlike run-time errors those can be caught by try... except
on...do ... end blocks, provided a mode allowing exceptions – such as {$mode ObjFPC} or {$mode Delphi} – is being used.
A run-time error causes the program to terminate, while an exception may give the opportunity to “fix” the problem.
This standard behavior of system.runError can be altered by assigning a non-nil value to system.errorProc.
