macOS Programming Tips

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Revision as of 07:10, 26 July 2020 by Trev (talk | contribs) (→‎Determining where to store files: Add new section)
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This article applies to macOS only.

See also: Multiplatform Programming Guide

English (en) 日本語 (ja) 한국어 (ko)

Cross compiling macOS applications on Linux

See Cross compiling macOS on Linux

Choice of Lazarus LCL widgetsets

With macOS there are various widgetsets which can be used with Lazarus. Each has its strengths and weaknesses.

Carbon widgetset (see the Carbon Interface page)

Pros Cons
All standard LCL controls working The entire Carbon framework has been deprecated by Apple. It is not available in 64 bit macOS applications. It was completely removed from macOS 10.15 Catalina (October 2019).
No additional libraries or frameworks to install; uses Carbon framework included with macOS
Native macOS look and feel Only relevant to macOS

Cocoa widgetset (see the Cocoa Interface page)

Pros Cons
All standard LCL controls working There may still be some minor bugs lurking; please report them!
No additional libraries or frameworks to install;
uses the Cocoa framework included with macOS
The only graphical framework for macOS 10.15 Catalina and later
Necessary for graphical 64 bit applications
Native macOS look and feel Only relevant to macOS

GTK widgetset

Pros Cons
All standard LCL controls working Ugly; clunky common dialogs; doesn't look like Mac software
This widgetset is well tested Requires X11 and bulky GTK to be installed to run Lazarus or any GUI apps created with Lazarus
Have to start Lazarus at command line -- can't double-click Lazarus or place on dock (same with GUI apps) -- although see Creating an app bundle for a GTK application for how you can add this capability yourself.

Qt widgetset (see the Qt Interface Mac page)

Pros Cons
Native macOS look and feel Requires the Qt interface framework to be installed to run app, which is rather large
All standard LCL controls working
The Qt widgetset also available for other platforms, so any effort put into developing Qt widgetset benefits multiple platforms
The Qt interface provides rich functionality
The Qt widgetset is easier to develop than other widgetsets

Creating an app bundle for a GTK application

macOS needs an app bundle for an executable file in order to drop it on the dock or launch it by double-clicking. An app bundle is really just a special folder that can have the same name as the executable, but with an .app extension. Finder doesn't display the .app extension, although you'll see it if you use the UNIX ls command in a Terminal window to list the directory contents. For details of how to create an app bundle for a GTK application, see Creating an app bundle for GTK applications.

Using Xcode for Pascal projects

For details of how to use Xcode for Pascal projects refer to this page.

Using stdout for logging and debugging

Using a Terminal

Unix systems usually allow output to stdout for GUI applications (while for Windows it requires creating a console object for stdout, using file handle as stdout or linking the application as a non-GUI). The output is really useful for debugging and logging purposes.

macOS GUI applications (the ones created by Lazarus) are deployed as bundles. The bundled application conceals the output. However, it is possible to see the output generated by a simple WriteLn(), by launching the application bundle's executable from a Terminal. Here are the steps:

  • Launch Terminal (found in /Applications/Utilities)
  • Change to the project directory
  • Launch the executable:
 $ ./
  • once MyApp is running, the output will be seen in the Terminal window


This is especially useful when using Project Options > Compiler Options > Debugging when you have ticked the Other debugging info - Use Heaprtc unit (check for mem-leaks). The Terminal will show the report:

  Heap dump by heaptrc unit of ./MyApp
  1441 memory blocks allocated : 99080/102040
  1441 memory blocks freed     : 99080/102040   
  0 unfreed memory blocks : 0
  True heap size : 458752 (32 used in System startup)
  True free heap : 458720

Using the Console

It is also possible to see the output by using the native macOS NSLog() procedure which logs your error message to the Apple System Log facility which you can read using the Console utility (located in Applications > Utilities). As there will be many message entries scrolling by, add MyApp to the search window to filter the entries being shown. For example:

  MyAudioPlayer := AVAudioPlayer.alloc.initWithContentsOfURL_error(url, @err);

  if Assigned(MyAudioPlayer) then
    NSLog(NSStr('Error in procedure PlayAudio(): %@'), err);

When the audio file is missing from the application's Resources directory, the following appears in the Console system log:

NSLog Console.png

Note that the NSlog information also appears in the Terminal if you have opened the application as explained above.

Deploying an application for an older version of the operating system

When compiling an application on without any special options, the application is only guaranteed to work on that particular major operating system release and later (eg when compiling under Snow Leopard 10.6.8, the application is only guaranteed to work on Snow Leopard 10.6.8 and later).

Here is an example of an error that you may encounter when running an application compiled for Leopard 10.5 under Tiger 10.4 in case you use the widestring manager:

dyld: Library not loaded: /usr/lib/libiconv.2.dylib
  Referenced from: /Volumes/..../yourprogram
  Reason: Incompatible library version: yourprogram requires version 7.0.0 or later, but libiconv.2.dylib provides version 5.0.0
Trace/BPT trap

Here is an example of an error that you may encounter when running an application compiled for Snow Leopard 10.6.8 under Snow Leopard 10.6.7:

Runtime error 203

FPC 2.6.2 and above

See the article Support for specifying and querying the deployment version which is current up to and including FPC 3.04.

For FPC 3.2 (aka fixes branch) see the article Default target macOS version.

Adding the custom options only when compiling for macOS

To add the above custom options only when compiling for macOS add to Project / Compiler options / IDE macros / Conditionals:

if TargetOS = 'darwin' then begin
  UsageCustomOptions += ' -WM10.6';

FPC 2.6.1 and below

See the FPC 2.6.1 macOS Targets article.

Useful commands and tools included with macOS


See the macOS Open Sesame article for the many uses of the macOS open command.

zip / unzip

These standard command-line programs are pre-installed.


Drag this app from /Applications/Utilities and drop it on the dock so you always have it handy. Launch it whenever you want to see messages or errors output to the console by GUI apps (for example, when they crash). Invaluable for debugging.

Activity Monitor

This app is also in /Applications/Utilities and is useful for monitoring CPU, memory, energy, network and disk usage.


Use otool to display information about an executable file or library. For example, enter the following to see information about Lazarus:

cd /usr/local/share/lazarus
otool –L lazarus

This shows that Lazarus is dependent on various libraries in /usr/lib and /System/Library/Frameworks/, as you would expect. Open a Terminal and type man otool to view its manual page.


Use install_name_tool with the –change switch to change where an executable file or library looks for a library that it requires. Open a Terminal and type man install_name_tool to view its manual page.


Use Grab (in /Applications/Utilities) to create a screenshot or window shot, then save it to a disk file. Note: replaced in recent versions of macOS by CMD+SHIFT+4 for image capture and CMD+SHIFT+5 for video capture (full or part screen).


Use iconutil in /usr/bin/ to create icon files (.icns) for use with your .app bundles. Open a Terminal and type man iconutil for its manual page.

pkgbuild, productbuild / Disk Utility

Use these apps to create disk image (.dmg) files for deploying your apps. See Deploying Your Application for more information.

Command line tools pkgbuild and productbuild are in /usr/bin/. Disk Utility is in /Applications/Utilities. You can drag and drop Disk Utility on the dock.

A popular third party option is the GUI application Packages ( which creates .pkg installer archives.

Script Editor / osascript

Use Script Editor to edit, compile and run AppleScript files. It’s located in /Applications/Utilities/.

Use osascript from /usr/bin to execute an AppleScript command or file from the command line or from a script file. For more information, enter man osascript in a Terminal to view its manual page.

Commonly used Unix commands

If you’re coming to macOS from Windows, you may find some of its Unix terminal commands confusing. Here are some equivalents. For more information about a command, enter man:command in Safari once you have Sogudi installed (see above).

Action Windows command prompt window macOS Terminal or X11 window
Change to a different directory cd cd
Make a new directory mkdir mkdir
Delete a directory rmdir rmdir
List file directory in chronological order with detail dir /od ls -ltr
Copy a file, preserving its date-time stamp copy cp -p
Display contents of a text file type cat
Delete a file erase rm
Move a file move mv
Rename a file ren mv
Find a file dir /s find
Grep a file findstr grep
Display differences between two text files fc diff
Change file attributes attrib chmod
“Super-user” root authorization N/A sudo
Create symbolic link to a file or directory mklink ln
Shrink executable file size strip (included w/ Free Pascal) strip


Using a library in a Mac application

Many software projects use external libraries to complement their functionality. For example, OpenAL might be utilized to provide sound support, or FreeType might be utilized to provide font rendering support for FCL-Image. macOS already comes with a number of open source libraries installed, being that OpenAL is one of them. If one of these libraries is utilized, one should simply add the corresponding import unit to the uses clause and start using the library. To use other open source libraries which aren't included with macOS, the easiest way is by grabbing a pre-compiled library from the application bundle of popular open source applications. FreeType for example is included inside the application bundle from Gimp in the path Another option is downloading the source code from the library and building it manually, but compiling a C library is usually an unpleasant task for Pascal developers.

So, again in the previous example, let's say that an application requires the FreeType library. One can grab the libfreetype.6.dylib file from Gimp and then place it in a location of our source code tree, for example ../Mac/libfreetype.dylib relative to the path of the main project file, which is where the executable is placed. To properly link the application the Free Pascal command line option "-Fl../Mac" should be added, so that this path is added to the library search path. The linker will then find the library in this location and read the install path which is written inside it. At runtime the linker will search for the library in this install path. To change the install path to our desired one, the command line application install_name_tool, which comes with the Apple Developer Tools, can be used. It can be utilized with the following command line command:

install_name_tool libfreetype.dylib -id @executable_path/../Frameworks/libfreetype.dylib

One can then verify if this command worked by using the command:

otool -D libfreetype.dylib

It should return the written path. When building the application bundle, we should copy the libfreetype.dylib file to the Frameworks sub-directory. The install_name_tool command uses the @executable_path macro to set an install path relative to the executable, which is inside the MacOS folder in the application bundle. Now the application can be built, the bundle and then the application can be run and it will load the library correctly from the application bundle.

Using a library installed using fink

For using libraries, which were installed using fink, you need to add the path to the libraries. The default is /sw/lib. Adding the option -Fl/sw/lib to the command line tells the linker where to find the libraries. The resulting application is fine for distribution with fink, but in order to run without fink, you have to make a "standalone" version. There are several possibilities to achieve this, one of them will be outlined here: First copy the .dylib file into the application bundle, for example to Contents/MacOS/ next to the executable binary. Then, adjust the paths install_name_tool:

First, change the path of the library in the executable:

install_name_tool  -change /sw/lib/libfreetype.dylib @executable_path/libfreetype.dylib @executable_path/your_executable_binary

Second, adjust the path in the library

install_name_tool  -id @executable_path/libfreetype.dylib @executable_path/libfreetype.dylib
install_name_tool  -change /sw/lib/libfreetype.dylib @executable_path/libfreetype.dylib @executable_path/libfreetype.dylib

The complete list of libraries in your executable can be obtained with:

otool -L @executable_path/your_executable_binary | grep version | cut -f 1 -d ' '

The list with libraries from fink only without libraries from /usr/lib and /System/Library gives this command:

otool -L @executable_path/your_executable_binary | grep version | cut -f 1 -d ' ' | grep -v \/System\/Library | grep -v \/usr\/lib

With this a script can be created, which loops over all libraries from fink in the executable.

Beware of the fact that the libraries can itself call libraries from fink. You have to adjust them as well.

Another important point of libraries from fink is, that they have only one architecture, i.e. i386, ppc, x86_64 or ppc64. For a universal application, you have to combine single architecture libraries with lipo.

How to obtain the path to the Bundle

function GetBundlePath(): string;
  pathRef: CFURLRef;
  pathCFStr: CFStringRef;
  pathStr: shortstring;
  pathRef := CFBundleCopyBundleURL(CFBundleGetMainBundle());
  pathCFStr := CFURLCopyFileSystemPath(pathRef, kCFURLPOSIXPathStyle);
  CFStringGetPascalString(pathCFStr, @pathStr, 255, CFStringGetSystemEncoding());
  Result := pathStr;

This returns the full path up to and including the application bundle name (eg /Users/Me/

Determining where to store files

Before we go any further, let's recap where the Apple Guidelines indicate your application should store its files:

  • Use the /Applications or /Applications/Utilities directory for the application bundle. The application bundle should contain everything: libraries, dependencies, help, every file that the application needs to run except those created by the application itself. If the application bundle is copied to another machine's /Applications or /Applications/Utilities directory, it should be able to run. Installing to these folders requires Admin privileges. The data in these folders is backed up by Time Machine.
  • Use the ~/Applications directory should Admin privileges not be available. This is the standard location for a single user application. This directory should not be expected to exist. The application bundle should contain everything: libraries, dependencies, help, every file that the application needs to run except those created by the application itself. If the application bundle is copied to another machine's /Applications or /Applications/Utilities directory, it should be able to run. This data is backed up by Time Machine.
  • Use the Application Support directory (this data is backed up by Time Machine), appending your <bundle_ID>, for:
    • Resource and data files that your application creates and manages for the user. You might use this directory to store application state information, computed or downloaded data, or even user created data that you manage on behalf of the user.
    • Autosave files.
  • Use the Caches directory (this is not backed up by Time Machine), appending your <bundle_ID>, for cached data files or any files that your application can recreate easily.
  • Use CFPreferences to read and write your application's preferences. This will automatically write preferences to the appropriate location and read them from the appropriate location. This data is backed up by Time Machine.
  • Use the application Resources directory (this is backed up by Time Machine) for your application-supplied image files, sound files, icon files and other unchanging data files necessary for your application's operation.
  • Use NSTemporaryDirectory (this is not backed up by Time Machine) to store temporary files that you intend to use immediately for some ongoing operation but then plan to discard later. Delete temporary files as soon as you are done with them.

Determing if a file is readable

There appears to be no reliable method to determine if a file is readable in all situations. ChrisR came up with this method which is reliable. You could also report a bug against Apple's isReadableFileAtPath method which is essentially a wrapper around the BSD access system call and does not take into account the various security and privacy features that Apple has added since macOS 10.0.

{$IFDEF Darwin}
function FileIsReadable(const AFilename: string): boolean;
  f: file;
  b: byte;
  Result := BaseUnix.FpAccess(AFilename, BaseUnix.R_OK) = 0;
  if not Result then exit; //globally not readable
  if FileSizeUtf8(AFilename) < 1 then exit(false);
  AssignFile(f, AFilename);
    FileMode := fmOpenRead;  //Set file access to read only
    Reset(f, 1);
    if ioresult <> 0 then
    b := 0;
    BlockRead(f, b, sizeof(b));
    result := true;
    result := false;
function FileIsReadable(const AFilename: string): boolean;
  Result := BaseUnix.FpAccess(AFilename, BaseUnix.R_OK) = 0;

Accessing system information

Sysctl provides an interface that allows you to retrieve many kernel parameters in macOS (and Linux and the BSDs). This provides a wealth of information detailing system hardware which can be useful when debugging user issues or simply optimising your application (eg to take advantage of threads on multi-core CPU systems). The NSProcessInfo class provides access to a collection of information about the current process. The IOKit framework implements non-kernel access to I/O Kit objects (eg to retrieve the Mac platform serial number and UUID). For full details and example code, see the article Accessing macOS System Information.

Retrieve username/ full username

The code to retrieve the current user's username (eg joe) or full username (eg Joe Bloggs) can be found in the article macOS Retrieve (full)username.

Making a beep

Procedure declaration:

procedure NSBeep; cdecl;
  external '/System/Library/Frameworks/AppKit.framework/AppKit' name 'NSBeep';

To use it:

procedure MakeBeep;


You can also assign NSBeep to the OnBeep (TBeepHandler in the SysUtils unit), by setting it on Form creation.

This way you can call the regular Beep function (by default, Beep contains no implementation to actually produce a beep).

procedure TForm1.FormCreate(Sender: TObject);
    OnBeep := @NSbeep;


Show application in all desktop spaces

An application defaults to showing only in the desktop space in which it was opened. To show your application in all desktop spaces for macOS 10.5+ (Leopard):

{$modeswitch objectivec1}

Uses CocoaAll ...

procedure TForm1.MenuItem35Click(Sender: TObject);
  theWindow: NSWindow;
  theWindow := NSView(Form1.Handle).window;       // Form1 is the name of the main form - adjust as necessary
  theWindow.setCollectionBehavior(theWindow.collectionBehavior or NSWindowCollectionBehaviorCanJoinAllSpaces);

Launch/Toggle full screen

To toggle an application window full screen for macOS 10.7+ (Lion):

{$modeswitch objectivec1}

Uses CocoaAll ...

procedure TForm1.Button1Click(Sender: TObject);
  Window: NSWindow;
  Window := NSView(Form1.Handle).window;

To launch your application full screen you can call the button event handler (as below) or move the button event handler code (above) to the form's on activate event handler:

procedure TForm1.FormActivate(Sender: TObject);

Creating Universal binaries

Lazarus will create an application tuned for a single CPU. With the Carbon Interface version of the LCL, this is either PowerPC or Intel i386 (32 bit). You may want to distribute your application as a 'Universal Binary', allowing users that may have either a PowerPC or Intel computer to use the program. To do this, you need to compile two versions of your application: one with PowerPC as the target CPU and one as Intel. Next, you need to stitch these two executables together using the macOS program "lipo" (installed with the other Xcode developer tools required by Lazarus). For example, consider two versions of the application 'myprogram'. One in the 'ppc' folder compiled for PowerPC and one in the 'intel' folder compiled for Intel CPUs. You can then combine these two to a univeral application by running this command:

 lipo -create ./ppc/myproj ./intel/myproj -output ./myproj

Now, copy the newly created application myproj inside your .app folder.

A note on 64 bit binaries: Depending on the version of macOS and after corresponding (cross-)compilers are installed, programs which do not use the LCL can also be built as ppc64 or x86_64 binaries, in particular command line utilities. lipo is used in the same way to put them into universal binaries.

Executable size optimisation

The normal way to optimise the size of your executable with Lazarus would be:

1. Project > Project Options > Compilation and Linking

  • Check Optimisation level 3 (-O3)
  • Check Smaller rather than faster (-Os)
  • Check Smart Linkable (-CX)
  • Check Link smart (-XX)

2. Project > Project Options > Debugging

  • Uncheck all except Strip Symbols From Executable (-Xs)

An example (Xcode 11.3; macOS Mojave 10.14.6):

  • MyApp compiled with Lazarus defaults (-O1) - executable size 12,011,600 bytes.
  • MyApp compiled with (-O3) - executable size - executable size 12,011,600 bytes.
  • MyApp compiled with (-O3) and (-Os) - executable size 12,011,592 bytes.
  • MyApp compiled with (-O3), (-Os) and (-CX) - executable size 12,011,592 bytes.
  • MyApp compiled with (-O3), (-Os), (-CX) and (-XX) - executable size 4,624,076 bytes!
  • MyApp compiled with (-O3), (-Os), (-CX), (-XX) and (-Xs) - executable size 4,624,076 bytes.

Problem: Whoa! Stripping symbols from the executable should have made a difference. The reason it did not make any difference is that Apple removed the ability to strip the symbol table from an executable in Xcode 3.1 (2007 Leopard 10.5). Previously, in Xcode 2.5 (2005 Tiger 10.4), the linker could strip the symbol table from 32 bit executables. So, providing the (-Xs) option to the linker has no effect at all.

Solution: The strip command line utility will strip the symbol table. Manually running strip MyApp in a Terminal resulted in the executable size further reducing from 4,624,076 bytes to 2,922,396 bytes.

Code Signing

Before macOS Sierra users had the option to allow the installation of applications from "anywhere", "the App Store" and "identified developers". From macOS Sierra on, the "anywhere" option was removed. Thereafter, clicking on an application to run it results in a scary dialog being presented to your users stating: "YourApp can't be opened because it is from an unidentified developer. Your security preferences allow installations of only apps from the App Store and identified developers". The only dialog option is to close it.

Users can still run your application, but they have to know they can right-click or control-click on your application and then they get another scary dialog stating "YourApp is from an unidentified developer. Are you sure you want to open it?" but this time the dialog has an "open" button and a pre-focussed "cancel" button.

Code signing an application that has been written in Lazarus and Free Pascal requires only a few steps that are described in the article Code Signing for macOS. Note: You will need to pay Apple $US 99 per year to be an "identified developer" and code sign your applications.


Beginning with macOS Mojave 10.14.5 all new or updated kernel extensions and all software from developers new to distributing with a Developer ID must also be notarized in order to run or users are prevented from running the application with a very scary dialog stating: "YourApp can't be opened because Apple cannot check it for malicious software. This software needs to be updated. Contact the developer for more information."

Beginning with macOS 10.15 Catalina (released in October 2019), notarization is required by default for all software. If your application is not notarised, your users get the very scary dialog stating: "YourApp can't be opened because Apple cannot check it for malicious software. This software needs to be updated. Contact the developer for more information." This is in addition to requiring the application to be code signed.

The steps to notarize an application are described in the article Notarization for macOS 10.14.5+.

Locale settings (date & time separator, currency symbol, ...)

On macOS, like on other Unix platforms, the RTL does not load the locale settings by default. They can be initialised in three ways. See the article Locale settings for macOS for details.

Apple-specific UI elements

The Apple user interface in macOS has a number of unique features (eg the Dock, Apple main menu bar, sheets, user notifications, etc). For details on how to provide these non-cross-platform features in your applications, see the article Apple-specific UI elements.

Accessibility for users with special needs

macOS includes a wide variety of features and assistive technologies, such as screen and cursor magnification, a full-featured screen reader, visual flash alerts, closed captioning support, and much more. Take advantage of these features to make your apps accessible to users with special needs. Please refer to the Accessibility article for more details.

LCL FontDialog workaround

The FontDialog.OnApplyClicked event handler is not supported in macOS. So this code will have no effect (the message will not be shown):

procedure TForm1.Button1Click(Sender: TObject);
procedure TForm1.FontDialog1ApplyClicked(Sender: TObject);
  ShowMessage('Apply Clicked');

The workaround is to restructure the code as follows:

procedure TForm1.Button1Click(Sender: TObject);
  if FontDialog1.Execute then
      ShowMessage('Apply Clicked');


The following articles are relevant for troubleshooting application issues:

Seek help in the forums:

Obscure native macOS error codes?

Finally, if the issue is in Free Pascal or Lazarus and not your own code:

Converting legacy code

Bxxx code macro replacements:

  • BAnd(i,j) = ((i) and (j))
  • BOr(i,j) = ((i) or (j))
  • BXOr(i,j) = ((i) xor (j))
  • Bsr(i,n) = ((i) shr (n))
  • Bsl(i,n) = ((i) shl (n))
  • BTST(i,n) = ((((i) shr (n)) and 1)=1)
  • BSet(i,n) = i:=(i) or (1 shl (n))
  • BClr(i,n) = i:=(i) and not (1 shl (n))

See also: Porting from Mac Pascal.

Other Interfaces

Platform specific Tips

Interface Development Articles

See also

External Links