How to define a preprocessor symbol in Xcode

Question

Is it possible to set a symbol for conditional compilation by setting up properties in an Xcode project?

My aim is to to create a symbol that is available to all files, without having to use import/include, so that a set of common classes can have a special behavior in some projects. Like the following, but with my own symbols.

#if TARGET_IPHONE_SIMULATOR
    ...
#endif

Related: "Add preprocessor macro to a target in xcode 6"

outis
– outis

2019-06-11 21:11:35 +00:00
Commented Jun 11, 2019 at 21:11 — outis
– outis, Commented Jun 11, 2019 at 21:11

jww · Accepted Answer · 2017-01-05 16:02:39Z

119

Go to your Target or Project settings, click the Gear icon at the bottom left, and select "Add User-Defined Setting". The new setting name should be GCC_PREPROCESSOR_DEFINITIONS, and you can type your definitions in the right-hand field.

Per Steph's comments, the full syntax is:

constant_1=VALUE constant_2=VALUE

Note that you don't need the '='s if you just want to #define a symbol, rather than giving it a value (for #ifdef statements)

edited Jan 5, 2017 at 16:02

jww

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answered Dec 15, 2008 at 3:50

Ben Gottlieb

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7 Comments

Steph Thirion Over a year ago

Thanks! To whoever interested, the syntax looks like "kVarOne=5 myVar=3.0" (without the quotes), I found it by trial and error. Ben could you edit your answer to specify that? Thanks again.

Ali Parr Over a year ago

Amazing answer. I still have hair because of this. Thank you thank you thank you. +1 (I wish it could be more)

Clay Bridges Over a year ago

FYI, as of Xcode 3.2.4, "Preprocessor Macros" maps to GCC_PREPROCESSOR_DEFINITIONS, and Xcode will not let you do a user-define anymore (since it is already available).

JTE Over a year ago

This is no longer a Gear icon on the lower left, but instead a Plus icon on the lower right (of the Build Settings tab of your target).

Radu Simionescu Over a year ago

you should update this response. there is no gear icon anymore

|

cdespinosa · Accepted Answer · 2009-01-26 05:36:57Z

86

You don't need to create a user-defined setting. The built-in setting "Preprocessor Macros" works just fine. alt text http://idisk.mac.com/cdespinosa/Public/Picture%204.png

If you have multiple targets or projects that use the same prefix file, use Preprocessor Macros Not Used In Precompiled Headers instead, so differences in your macro definition don't trigger an unnecessary extra set of precompiled headers.

answered Jan 26, 2009 at 5:36

cdespinosa

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2 Comments

Kevin Laity Over a year ago

What do you do if this section is missing from the build settings?

Clay Bridges Over a year ago

Do what Ben Gotliebb suggests. But as of version 3.2.4 of Xcode, "Preprocessor Macros" maps to GCC_PREPROCESSOR_DEFINITIONS. You cannot user-define something already available.

Stickley · Accepted Answer · 2012-01-09 18:34:07Z

44

As an addendum, if you are using this technique to define strings in your target, this is how I had to define and use them:

In Build Settings -> Preprocessor Macros, and yes backslashes are critical in the definition:

APPURL_NSString=\@\"www.foobar.org\"

And in the source code:

objectManager.client.baseURL = APPURL_NSString;

answered Jan 9, 2012 at 18:34

Stickley

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1 Comment

David P Over a year ago

Thanks for this solution, been searching for something EXACTLY like this, yet stack overflow is full of over complicated solutions.

chunkyguy · Accepted Answer · 2012-01-20 23:51:54Z

5

You can use the *_Prefix.pch file to declare project wide macros. That file is usually in you Other Sources group.

answered Jan 20, 2012 at 23:51

chunkyguy

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Comments

Petr Javorik · Accepted Answer · 2018-07-31 09:21:19Z

5

For Xcode 9.4.1 and C++ project. Adding const char* Preprocessor Macros to both Debug and Release builds.

Select your project
Select Build Settings
Search "Preprocessor Macros"
Open interactive list
Add your macros and don't forget to escape quotation

Use in source code as common const char*

...
#ifndef JSON_DEFINITIONS_FILE_PATH
static constexpr auto JSON_DEFINITIONS_FILE_PATH = "definitions.json";
#endif
...
FILE *pFileIn = fopen(JSON_DEFINITIONS_FILE_PATH, "r");
...

answered Jul 31, 2018 at 9:21

Petr Javorik

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Comments

hEADcRASH · Accepted Answer · 2009-09-06 01:27:52Z

4

It's under "GCC 4.2 Preprocessing" (or just put "prepro" in the search box)...

...however, for the life of me I can't get it to work.

I have my standard Debug and Release configurations, and I want to define DEBUG=1 in the debugging configuration. But after adding it as a value:

(in the settings window) > Preprocessor Macros : DEBUG=1

#if DEBUG
    printf("DEBUG is set!");
#endif

...never prints/gets called. It's driving me crazy...

answered Sep 6, 2009 at 1:27

hEADcRASH

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2 Comments

Simo Salminen Over a year ago

Instead of #if DEBUG, try #if defined(DEBUG) or #ifdef DEBUG

jeff-h Over a year ago

Strangely enough, I found myself here in 2019, with Swift and Xcode 10.3. Anyone with the same issue described above might find this helpful; it certainly brought my #if DEBUG to life :) stackoverflow.com/a/47395485/2778502

Mark24x7 · Accepted Answer · 2010-04-22 16:50:25Z

1

In response to Kevin Laity's comment (see cdespinosa's answer), about the GCC Preprocessing section not showing in your build settings, make the Active SDK the one that says (Base SDK) after it and this section will appear. You can do this by choosing the menu Project > Set Active Target > XXX (Base SDK). In different versions of XCode (Base SDK) maybe different, like (Project Setting or Project Default).

After you get this section appears, you can add your definitions to Processor Macros rather than creating a user-defined setting.

answered Apr 22, 2010 at 16:50

Mark24x7

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Comments

kslcam · Accepted Answer · 2010-09-08 03:49:42Z

0

You can duplicate the target which has the preprocessing section, rename it to any name you want, and then change your Preprocessor macro value.

answered Sep 8, 2010 at 3:49

kslcam

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