Use of external C++ headers in Objective-C

#include <bla.h>

is meant for standard library or framework headers, and the search strategy Is different than that used for

#include "bla.h"

See for example

• What is the difference between #include <filename> and #include "filename"?

As a workaround, you can set the Xcode build setting "Always Search User Paths" to YES.

Starting from a "blank" application project:

1. Create a folder "Libraries" in your application's project - preferable as a sibling to your MyApp.xcodeproj file, but it can be anywhere. Create subfolders for each Configuration (Debug, Release, etc.) and possibly for each architecture (armv7, armv7s, arm64) unless the binary is universal binary archive containing all architectures.

2. Get the headers of the third party library and the static library binaries (possibly more than one for different platforms, Configurations and architectures) and move them into the "Library" folder into corresponding subfolders (which you may need to create):

   For example, assuming you had a universal binary (armv7, armv7s, arm64) and Debug and Release versions of that library: Now, the folder structure is assumed to be as follows:

   $(SRCROOT)/Libraries
       Debug-iphoneos
           include
               ThirdParty
                   third_party.hh 
                   ...
           libThirdParty.a             
       Release-iphoneos
           include
               ThirdParty
                   third_party.hh 
                   ...
           libThirdParty.a             
   MyApp.xcodeproj            
   

3. "Library Search Paths" Build Setting:

   Drag the "Libraries" folder into your Xcode project. This may automatically create a library search path in the build settings. Please verify this, and if it is not correct, fix it.

   Given the example, add the following library search paths for Debug and Release Configuration:

   Debug: Library Search Paths: $(SRCROOT)/Libraries/Debug-iphoneos

   Release: Library Search Paths: $(SRCROOT)/Libraries/Release-iphoneos

   You may have different library search paths for particular Configuration and Target platform pairs. Set different path's in the build setting accordingly.

4. "Header Search Paths" Build Setting:

   Given the example, add the following header search path to the Debug and the Release Configuration:

   Debug: Header Search Paths: $(SRCROOT)/Libraries/Debug-iphoneos/include

   Release: Header Search Paths: $(SRCROOT)/Libraries/Release-iphoneos/include

   Likewise, you may have different paths for particular Config/Target pairs - although the headers may be the same.

5. Link your app against the C++ standard library by adding -lc++ to the Other Linker Flags build setting.

6. Import the header in your files as follows:

    #import <ThirdParty/third_party.hh>