> For your reference, here on my MacOSX 10.14.6 with XCode 11.3.1 the pthread.h file is present in locations listed below.
> 
> Did you execute "xcode-select --install" ?
> 
> 
> ~$ locate pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/pthread/pthread.h
> /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/pthread.h
> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/pthread/pthread.h
> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/pthread.h

Hi Stefan,

Thanks for looking into this. Yes, I have done  "xcode-select --install"

This is my output when I try to locate pthread.h

Darrens-Mac-mini:~ betacage$ locate pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/WatchOS.platform/Developer/SDKs/WatchOS.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/WatchSimulator.platform/Developer/SDKs/WatchSimulator.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/usr/include/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/pthread/pthread.h
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/usr/include/pthread.h
/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/pthread/pthread.h
/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/pthread.h
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/pthread/pthread.h
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include/pthread.h

and this is what I see in my SDKs folder 

Darrens-Mac-mini:SDKs betacage$ pwd
/Library/Developer/CommandLineTools/SDKs
Darrens-Mac-mini:SDKs betacage$ ls
MacOSX.sdk	MacOSX10.14.sdk	MacOSX10.15.sdk

So it looks like in this computer one needs to read the version of the SDK as pthread.h is not in MacOSX.sdk but in MacOSX10.15.sdk

Thanks 

Berta