Xcode – Linking static libraries, that share another static library

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I currently have a single Xcode project for a very large code base, I'll call it Project X, which I am dividing into a bunch of sub projects ( Projects A, B, C ).

So far, each of these projects compiles, on their own, just fine. They all produce static libraries. Project B and Project C are dependent on the static library produced by Project A in order to build.

I have another xcode project, Project Z, that requires the static libraries produced by Projects B and C. Herein lies the problem. When Project Z enters the linker phase, things blow up – duplicate symbols are found within the libs for Projects B and C for the code they originally linked against in Project A!

I'm pretty new to the world of static libraries, and I'm unsure of how to move forward with Project Z, or how to modify the other projects so that they are linking against the same Project A lib. I have a feeling it's not possible. What are my options here?

Edit:

I should clarify that Project B and Project C need to build into separate static libs because some clients will only require one or the other.

Also, I'm having this dilemma on both OSX and iOS platforms.

I realize that I could solve this problem on OSX by building the projects as dynamic libraries. However, I'd prefer not to do this, and it still leaves me with same issue on iOS.

Best Answer

Static libraries should never include other static libraries (or third party code in general). A static library is just a bundle of .o files glued together. So if you have multiple copies of the same information, it's going to blow up.

Each static library should just have its own code in it. The final application is responsible for linking all the required libraries together (including libraries required by libraries). This way there is exactly one copy of each thing linked.

Related Solutions

C++ – Difference between static and shared libraries

Shared libraries are .so (or in Windows .dll, or in OS X .dylib) files. All the code relating to the library is in this file, and it is referenced by programs using it at run-time. A program using a shared library only makes reference to the code that it uses in the shared library.

Static libraries are .a (or in Windows .lib) files. All the code relating to the library is in this file, and it is directly linked into the program at compile time. A program using a static library takes copies of the code that it uses from the static library and makes it part of the program. [Windows also has .lib files which are used to reference .dll files, but they act the same way as the first one].

There are advantages and disadvantages in each method:

Shared libraries reduce the amount of code that is duplicated in each program that makes use of the library, keeping the binaries small. It also allows you to replace the shared object with one that is functionally equivalent, but may have added performance benefits without needing to recompile the program that makes use of it. Shared libraries will, however have a small additional cost for the execution of the functions as well as a run-time loading cost as all the symbols in the library need to be connected to the things they use. Additionally, shared libraries can be loaded into an application at run-time, which is the general mechanism for implementing binary plug-in systems.
Static libraries increase the overall size of the binary, but it means that you don't need to carry along a copy of the library that is being used. As the code is connected at compile time there are not any additional run-time loading costs. The code is simply there.

Personally, I prefer shared libraries, but use static libraries when needing to ensure that the binary does not have many external dependencies that may be difficult to meet, such as specific versions of the C++ standard library or specific versions of the Boost C++ library.

Iphone – Build fat static library (device + simulator) using Xcode and SDK 4+

ALTERNATIVES:

Easy copy/paste of latest version (but install instructions may change - see below!)

Karl's library takes much more effort to setup, but much nicer long-term solution (it converts your library into a Framework).

Use this, then tweak it to add support for Archive builds - c.f. @Frederik's comment below on the changes he's using to make this work nicely with Archive mode.

RECENT CHANGES: 1. Added support for iOS 10.x (while maintaining support for older platforms)

Info on how to use this script with a project-embedded-in-another-project (although I highly recommend NOT doing that, ever - Apple has a couple of show-stopper bugs in Xcode if you embed projects inside each other, from Xcode 3.x through to Xcode 4.6.x)
Bonus script to let you auto-include Bundles (i.e. include PNG files, PLIST files etc from your library!) - see below (scroll to bottom)
now supports iPhone5 (using Apple's workaround to the bugs in lipo). NOTE: the install instructions have changed (I can probably simplify this by changing the script in future, but don't want to risk it now)
"copy headers" section now respects the build setting for the location of the public headers (courtesy of Frederik Wallner)
Added explicit setting of SYMROOT (maybe need OBJROOT to be set too?), thanks to Doug Dickinson

SCRIPT (this is what you have to copy/paste)

For usage / install instructions, see below

##########################################
#
# c.f. https://stackoverflow.com/questions/3520977/build-fat-static-library-device-simulator-using-xcode-and-sdk-4
#
# Version 2.82
#
# Latest Change:
# - MORE tweaks to get the iOS 10+ and 9- working
# - Support iOS 10+
# - Corrected typo for iOS 1-10+ (thanks @stuikomma)
# 
# Purpose:
#   Automatically create a Universal static library for iPhone + iPad + iPhone Simulator from within XCode
#
# Author: Adam Martin - http://twitter.com/redglassesapps
# Based on: original script from Eonil (main changes: Eonil's script WILL NOT WORK in Xcode GUI - it WILL CRASH YOUR COMPUTER)
#

set -e
set -o pipefail

#################[ Tests: helps workaround any future bugs in Xcode ]########
#
DEBUG_THIS_SCRIPT="false"

if [ $DEBUG_THIS_SCRIPT = "true" ]
then
echo "########### TESTS #############"
echo "Use the following variables when debugging this script; note that they may change on recursions"
echo "BUILD_DIR = $BUILD_DIR"
echo "BUILD_ROOT = $BUILD_ROOT"
echo "CONFIGURATION_BUILD_DIR = $CONFIGURATION_BUILD_DIR"
echo "BUILT_PRODUCTS_DIR = $BUILT_PRODUCTS_DIR"
echo "CONFIGURATION_TEMP_DIR = $CONFIGURATION_TEMP_DIR"
echo "TARGET_BUILD_DIR = $TARGET_BUILD_DIR"
fi

#####################[ part 1 ]##################
# First, work out the BASESDK version number (NB: Apple ought to report this, but they hide it)
#    (incidental: searching for substrings in sh is a nightmare! Sob)

SDK_VERSION=$(echo ${SDK_NAME} | grep -o '\d\{1,2\}\.\d\{1,2\}$')

# Next, work out if we're in SIM or DEVICE

if [ ${PLATFORM_NAME} = "iphonesimulator" ]
then
OTHER_SDK_TO_BUILD=iphoneos${SDK_VERSION}
else
OTHER_SDK_TO_BUILD=iphonesimulator${SDK_VERSION}
fi

echo "XCode has selected SDK: ${PLATFORM_NAME} with version: ${SDK_VERSION} (although back-targetting: ${IPHONEOS_DEPLOYMENT_TARGET})"
echo "...therefore, OTHER_SDK_TO_BUILD = ${OTHER_SDK_TO_BUILD}"
#
#####################[ end of part 1 ]##################

#####################[ part 2 ]##################
#
# IF this is the original invocation, invoke WHATEVER other builds are required
#
# Xcode is already building ONE target...
#
# ...but this is a LIBRARY, so Apple is wrong to set it to build just one.
# ...we need to build ALL targets
# ...we MUST NOT re-build the target that is ALREADY being built: Xcode WILL CRASH YOUR COMPUTER if you try this (infinite recursion!)
#
#
# So: build ONLY the missing platforms/configurations.

if [ "true" == ${ALREADYINVOKED:-false} ]
then
echo "RECURSION: I am NOT the root invocation, so I'm NOT going to recurse"
else
# CRITICAL:
# Prevent infinite recursion (Xcode sucks)
export ALREADYINVOKED="true"

echo "RECURSION: I am the root ... recursing all missing build targets NOW..."
echo "RECURSION: ...about to invoke: xcodebuild -configuration \"${CONFIGURATION}\" -project \"${PROJECT_NAME}.xcodeproj\" -target \"${TARGET_NAME}\" -sdk \"${OTHER_SDK_TO_BUILD}\" ${ACTION} RUN_CLANG_STATIC_ANALYZER=NO" BUILD_DIR=\"${BUILD_DIR}\" BUILD_ROOT=\"${BUILD_ROOT}\" SYMROOT=\"${SYMROOT}\"

xcodebuild -configuration "${CONFIGURATION}" -project "${PROJECT_NAME}.xcodeproj" -target "${TARGET_NAME}" -sdk "${OTHER_SDK_TO_BUILD}" ${ACTION} RUN_CLANG_STATIC_ANALYZER=NO BUILD_DIR="${BUILD_DIR}" BUILD_ROOT="${BUILD_ROOT}" SYMROOT="${SYMROOT}"

ACTION="build"

#Merge all platform binaries as a fat binary for each configurations.

# Calculate where the (multiple) built files are coming from:
CURRENTCONFIG_DEVICE_DIR=${SYMROOT}/${CONFIGURATION}-iphoneos
CURRENTCONFIG_SIMULATOR_DIR=${SYMROOT}/${CONFIGURATION}-iphonesimulator

echo "Taking device build from: ${CURRENTCONFIG_DEVICE_DIR}"
echo "Taking simulator build from: ${CURRENTCONFIG_SIMULATOR_DIR}"

CREATING_UNIVERSAL_DIR=${SYMROOT}/${CONFIGURATION}-universal
echo "...I will output a universal build to: ${CREATING_UNIVERSAL_DIR}"

# ... remove the products of previous runs of this script
#      NB: this directory is ONLY created by this script - it should be safe to delete!

rm -rf "${CREATING_UNIVERSAL_DIR}"
mkdir "${CREATING_UNIVERSAL_DIR}"

#
echo "lipo: for current configuration (${CONFIGURATION}) creating output file: ${CREATING_UNIVERSAL_DIR}/${EXECUTABLE_NAME}"
xcrun -sdk iphoneos lipo -create -output "${CREATING_UNIVERSAL_DIR}/${EXECUTABLE_NAME}" "${CURRENTCONFIG_DEVICE_DIR}/${EXECUTABLE_NAME}" "${CURRENTCONFIG_SIMULATOR_DIR}/${EXECUTABLE_NAME}"

#########
#
# Added: StackOverflow suggestion to also copy "include" files
#    (untested, but should work OK)
#
echo "Fetching headers from ${PUBLIC_HEADERS_FOLDER_PATH}"
echo "  (if you embed your library project in another project, you will need to add"
echo "   a "User Search Headers" build setting of: (NB INCLUDE THE DOUBLE QUOTES BELOW!)"
echo '        "$(TARGET_BUILD_DIR)/usr/local/include/"'
if [ -d "${CURRENTCONFIG_DEVICE_DIR}${PUBLIC_HEADERS_FOLDER_PATH}" ]
then
mkdir -p "${CREATING_UNIVERSAL_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"
# * needs to be outside the double quotes?
cp -r "${CURRENTCONFIG_DEVICE_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"* "${CREATING_UNIVERSAL_DIR}${PUBLIC_HEADERS_FOLDER_PATH}"
fi
fi

INSTALL INSTRUCTIONS

Create a static lib project
Select the Target
In "Build Settings" tab, set "Build Active Architecture Only" to "NO" (for all items)
In "Build Phases" tab, select "Add ... New Build Phase ... New Run Script Build Phase"
Copy/paste the script (above) into the box

...BONUS OPTIONAL usage:

OPTIONAL: if you have headers in your library, add them to the "Copy Headers" phase
OPTIONAL: ...and drag/drop them from the "Project" section to the "Public" section
OPTIONAL: ...and they will AUTOMATICALLY be exported every time you build the app, into a sub-directory of the "debug-universal" directory (they will be in usr/local/include)
OPTIONAL: NOTE: if you also try to drag/drop your project into another Xcode project, this exposes a bug in Xcode 4, where it cannot create an .IPA file if you have Public Headers in your drag/dropped project. The workaround: dont' embed xcode projects (too many bugs in Apple's code!)

If you can't find the output file, here's a workaround:

Add the following code to the very end of the script (courtesy of Frederik Wallner): open "${CREATING_UNIVERSAL_DIR}"
Apple deletes all output after 200 lines. Select your Target, and in the Run Script Phase, you MUST untick: "Show environment variables in build log"
if you're using a custom "build output" directory for XCode4, then XCode puts all your "unexpected" files in the wrong place.
1. Build the project
2. Click on the last icon on the right, in the top left area of Xcode4.
3. Select the top item (this is your "most recent build". Apple should auto-select it, but they didn't think of that)
4. in the main window, scroll to bottom. The very last line should read: lipo: for current configuration (Debug) creating output file: /Users/blah/Library/Developer/Xcode/DerivedData/AppName-ashwnbutvodmoleijzlncudsekyf/Build/Products/Debug-universal/libTargetName.a
...that is the location of your Universal Build.

How to include "non sourcecode" files in your project (PNG, PLIST, XML, etc)

Do everything above, check it works
Create a new Run Script phase that comes AFTER THE FIRST ONE (copy/paste the code below)
Create a new Target in Xcode, of type "bundle"
In your MAIN PROJECT, in "Build Phases", add the new bundle as something it "depends on" (top section, hit the plus button, scroll to bottom, find the ".bundle" file in your Products)
In your NEW BUNDLE TARGET, in "Build Phases", add a "Copy Bundle Resources" section, and drag/drop all the PNG files etc into it

Script to auto-copy the built bundle(s) into same folder as your FAT static library:

echo "RunScript2:"
echo "Autocopying any bundles into the 'universal' output folder created by RunScript1"
CREATING_UNIVERSAL_DIR=${SYMROOT}/${CONFIGURATION}-universal
cp -r "${BUILT_PRODUCTS_DIR}/"*.bundle "${CREATING_UNIVERSAL_DIR}"

Best Answer

Related Solutions

C++ – Difference between static and shared libraries

Iphone – Build fat static library (device + simulator) using Xcode and SDK 4+

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