Debugging Techniques

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Debugging Techniques are ways for a developers to debug (narrow down/determine the root source), or to learn and understand where and why errors or unexpected outcomes are occurring within their code.

Debugging is the process of finding and resolving defects or problems within a computer program that prevent correct operation of computer software or a system – Wikipedia - Debugging'


Code basics

Various links about code and how to write it:

IDE and Syntax Highlight

Syntax errors are a frequent occurrence when developing scripts. Syntax highlight will help you find typos in commands and in your scripts.

An Integrated Development Environment (short IDE) is a development environment software that provides among other things code analysis, code completion and syntax highlight to help you write better, more error free code.

See further Debugging Tools page section for download links.

Errors

An error in SQF will purely and simply halt the current script, leading to unpredictable behavior. Error are not to happen as it may reduce performance as well as break a mission/feature. So if you notice an issue, address it as your script will stop.

Finding Errors

Debugging is usually as complicated as writing the actual code itself. You usually get hinted by the game, where some error happened, and what it was.
There are instances where actual error reason might be something completely different than announced (eg. you get the error on a variable being nil somewhere, but the actual error is that you mistyped it where you set it initially).

Make sure you enable Show Script Errors in the Launcher (for Arma 3) or set the corresponding -showScriptErrors startup parameter.

A script error will greet you with this box:

Script error message

It tells you what went wrong, shows a snippet of the code that failed and what file and line it occurred in (unless you used a command combination like eg. compile loadFile). Knowing this, you now can proceed to find the actual reason why that specific piece of code errored.

This information can also be found in the RPT log.

To solve an issue, you must first to became aware that of it. Aside from your script not having the desired result/effect (if any), an error message can tell you about the problem.

RPT files

The RPT is also used by the game's engine log other type of problems (low level engine issues, or content problems for example). Hence it will dump all kinds of debug information, warnings, errors as well as encountered script errors. One can also write information to it by using commands like diag_log.

The RPT file might be disabled using the Arma 3 launcher or by setting the corresponding -noLogs startup parameter (Arma 3 or Arma 2: Operation Arrowhead option)
RPT File location per game (See Crash Files for more information)
Game Location Files
Introduced with Arma 3 version 1.00
Arma 3
%localappdata%\Arma 3 Arma3_x64_yyyy-mm-dd_hh-mm-ss.rpt
Introduced with Arma 2 version 1.00
Arma 2
%localappdata%\ArmA 2 arma2.rpt
Introduced with Armed Assault version 1.00
Armed Assault
%localappdata%\ArmA arma.rpt
Introduced with Operation Flashpoint version 1.00
Operation Flashpoint
OFP root directory flashpoint.rpt
context.bin

Solving Errors

Once the script error is located: Make sure to check first the BiKi page corresponding to the command/function you are using to learn about potential misuse or other important information mentioned on the page!

The most simple thing you can do is to output expected values. This can be done using for example diag_log or systemChat. Output yourself a few variables that relate to your problem (for example: When the error occurs because you land in some if block, output the corresponding variables inside of the if). You continue doing this until you hit the actual problem: When variable A is not set, go to where variable A gets set and check around there, repeat and continue.

The same can be done for non-critical errors like when a method is "just" computing the wrong values.

If you're having great difficulty solving a problem, the good way is to narrow down the issue to the simplest code block possible; or take the mission part that doesn't work, paste it into a new test mission and go from here.

Doing so will save you dealing with other scripts' potential side effects!

Common errors

Error message Cause Solution
Error Undefined variable in expression: _varName variable _varName has not been initialised properly in this context.

hint _nonExistentVar;

  • in the case of a spawned code, previous local variables are not accessible and must be passed as arguments in order to access them.
  • a variable may have been undefined (_varName = nil). Unset it after you are done using it.
Error x elements provided, y is expected A wrong number of arguments in array was provided

_unit setPos [0]; // setPos only takes an array of 2 to 3 elements

Read the wiki about said command.

Use typeName to output a variable type and compare it to the command's wiki page.
Error type x, expected y An ill-typed argument was provided.

hint 5; // must be String or Structured Text, Number provided

Error Zero divisor Pretty self-explanatory, somewhere in the code is a division by zero.

private _number = 0; private _result = 100/_number;

  • Make sure to check that your divisor is different from zero before dividing.

private _result = [100, 100/_number] select (_number != 0);

Also happens when using an invalid select index.

["a","b","c"] select 20; // index can only be 0, 1 or 2

  • Ensure your select happens within the array boundaries.
  • use selectRandom to pick a random item in an array.
Local variable in global space An attempt to private a public variable happened

private "myVar"; // should be "_myVar"

  • Replace public variable usage with private variables.
Error Generic error in expression A sleep/uiSleep/waitUntil command has been used in an unscheduled environment.

player addEventHandler ["Fired", { sleep 1; hint "bang"; }];

  • Do not use such suspending commands in unscheduled environment.
  • For an FSM condition, a common workaround would be:

private _t = time + 5; // Code - having to wait for 5 seconds time > _t // Condition

player addEventHandler ["Fired", { [] spawn { sleep 1; hint "bang"; }; }];

Further code reading is required.
  • cut your code in smaller pieces and locate the concerned line(s).

Working with Addons

If you are working on an addon, repacking a PBO can be time-intensive. This operation can be replaced simply by creating a basic mission in the "Missions" or "MPmissions" (if your feature is multiplayer-specific) folder of your game installation, and running the mission locally. The easiest way of accomplishing this is by the use of Event Scripts to run your code such as init.sqf. Once you have tested your code this way, you can then sequentially pack your PBO when major changes have been made, rather than for each debug session of a script or piece of code.

Debugging specific sections of code

Although primitive, the combined use of diag_log, systemChat/hint and format can help to debug the content of function arguments. In the case that specific pieces of code do not run, or if specific if conditions don't appear to fire, debugging the variable content with diag_log can be useful. As with all debugging, as long as the developer is methodical and logical in checking each section of code that runs, finding bugs and resolving them can be straightforward.


Debugging Tools

Code Edition

User Addon/Toolname Category Description Link
Sanjo Notepad++ SQF Text editor plugin - Notepad++ Notepad++ SQF Syntax highlighter plugin. Forum post Download
K-Town Arma IntelliJ plugin IDE plugin - IntelliJ Forum post Download
Armitxes SQF Language IDE plugin - Visual Studio Code Forum post Download
ole1986 Arma Dev IDE plugin - Visual Studio Code Download
SkaceKachna SQFLint IDE plugin - Visual Studio Code Forum post Download
krzmbrzl SQDev IDE plugin - Eclipse Provides code validation (linting) while you are typing it. Forum post Download
Sbsmac Squint IDE Provides a fully-featured code editor which allows for syntax highlighting, displaying of errors and code correction. Forum post Download

Debug Console/Systems

Game User Addon/Toolname Category Description Link
Introduced with Arma 3 version 1.00
Bohemia Interactive N/A Debug console Debug Console capable of executing code and more. Wiki page
Introduced with Arma 3 version 1.00
Kju DevCon Debug console Download
Introduced with Take On Helicopters version 1.00
Bohemia Interactive N/A Debug console Debug Console capable of executing code and more. Wiki page
Introduced with Arma 2 version 1.00
Kju DevCon Debug console Download
Introduced with Arma 2 version 1.00
Charon Productions TroopMon v3 Debug system Debugging system containing informations relevant to mission-makers (especially about AI) Download
Introduced with Arma 2 version 1.00
Str Debug console Download
Introduced with Armed Assault version 1.00
Charon Productions TroopMon v0.8b Debug system Complex debugging system providing lots of information for mission-makers, especially about AI. Download
Introduced with Armed Assault version 1.00
Str Debug console available in all singleplayer missions, intros and outros. Easy and simple to use (Escape-Enter execute) Download

SQF and debug Tools

User Addon/Toolname Category Description Link
X39 SQF VM Emulator Forum post Download
Dedmen Arma Script Profiler Profiler Can be used to profile scripts and engine. Forum post Download
Dedmen Arma Debug Engine Debugger Workshop link Download