How to create a framework that uses C with Xcode

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Step 1:  Create a Cocoa Touch Framework

File -> New -> Project -> Cocoa Touch Framework

Xcode new project dialog highlighting Cocoa Touch Framework template

Name it SwiftCFramework

Step 2: Create xcconfig file:

Finder save dialog creating a new xcconfig file

Xcode build configuration files, more commonly known by their [xcconfig](https://nshipster.com/xcconfig/) file extension, allow build settings for your app to be declared and managed without Xcode.

Step 3: Add xcconfig to the Configurations section of the Project Info

Xcode project info showing custom xcconfig configuration selection

Step 4: Add swiftcframework.mapmodule and public.mapmodule files to the project

Xcode file navigator with module map files added to the framework

Module map file contents displayed in Xcode editor

Step 5: Add C header files and make sure their Target Membership is set to Private

Project navigator showing C header files with private target membership

Step 6: Add a run script to remove private headers and create a public modulemap file

Name the script “Make C Header Files Private”

Run script build phase removing private headers and copying module map 

# Delete PrivateHeaders folder
rm -rf ${TARGET_BUILD_DIR}/${PRODUCT_NAME}${WRAPPER_SUFFIX}/PrivateHeaders

# Remove module.modulemap file
rm ${TARGET_BUILD_DIR}/${PRODUCT_NAME}${WRAPPER_SUFFIX}/Modules/module.modulemap

# Copy public.modulemap file and rename it to module.modulemap
cp ${SRCROOT}/Supporting/public.modulemap ${TARGET_BUILD_DIR}/${PRODUCT_NAME}${WRAPPER_SUFFIX}/Modules/module.modulemap

# Append the Swift module so you can access you Swift code in Objective-C via @import MyFramework.Swift
echo "module ${PRODUCT_NAME}.Swift { header \"${PRODUCT_NAME}-Swift.h\" }" >> ${TARGET_BUILD_DIR}/${PRODUCT_NAME}${WRAPPER_SUFFIX}/Modules/module.modulemap

Step 7: Add the framework to a test application

Test application target linked with the custom framework in Xcode

The code is available on the SwiftCFramework GitHub repository.

FAQ

How do I create a Swift framework that wraps C code in Xcode?
Create a Cocoa Touch Framework target, configure an xcconfig file for build settings, add C headers and module map files to describe your C APIs, and then link the framework into a sample app so Swift code can import and call the C functions.
How can I keep C headers private while still exposing them through a module map?
Mark C headers as Private in the framework target and add a run script build phase that removes the PrivateHeaders folder, replaces the default module.modulemap with a curated public.modulemap, and appends a Swift submodule entry so Objective-C can import the generated Swift header.

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