Using External Project to built and add non-cmake library to project

Usage
1

Hello I’m currently trying to build a library using CMake and I would
like to add a specific library to it.

My goal is to be able to bundle the sources with my library source and
make them build alongside my own.

I found out about ExternalProject but I have a hard time understanding
the way to use it.

My current project file is organised as such:


.

./include

./src

./external

./external/libA/

./external/libA/CMakeLists.txt

./external/libB/

./CMakeLists.txt

libA is built using Cmake so I had not much trouble adding it.

However libB using plain makefiles, and to built it I roughly must use
the following command:


make -f <specific make file>

I tried the following:

ExternalProject_Add(libB
     PREFIX ${CMAKE_CURRENT_BINARY_DIR}/libB
     SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/${LIBB_DIR}
     BUILD_COMMAND make -f Makefile.linux.alt
     BUILD_IN_SOURCE 1
)

Once I tried running make I get the following:


CMake Error: The source directory "LIBD_DIR" does not appear to contain 
CMakeLists.txt.

Which sounds weird to me because that is exactly what I wanted to avoid
using in the first place.

Can someone explain me what am I doing wrong ?

2

You probably want to pass CONFIGURE_COMMAND and INSTALL_COMMAND parameters as empty strings to disable them.

3

It worked!!!

Thanks you

4

I just noticed a thing. While my lib build without error, while checking the built mylib.a I noticed that none of libB.a symbols are available.

In order to link the built libB to mine I used the following command:


ExternalProject_Get_property(LIBB SOURCE_DIR)
target_link_libraries(${PROJECT_NAME} PUBLIC ${SOURCE_DIR}/libB.a)
target_include_directories(${PROJECT_NAME} PUBLIC ${SOURCE_DIR}/liB_include)

using nm -gC mylib.a | grep <specific libB symbols> none are displayed.

I also noticed that building a program that includes mylib result in a


make[2]: *** No rule to build target « mylib/${SOURCE_DIR}/libB.a », required for « project ». Stopping.

Any idea what I’ve overlooked ?

5

mylib.a looks to be an archive library so it doesn’t have a linking step. None of the symbols of libB would be expected to show up. If you made mylib a shared library then there is usually a linking step and you would see the libB symbols. I don’t think CMake supports combining archive files.

6

The thing is some of the features of mylib.a must uses features from libB.a.

Maybe I’m doing this wrong, it’s my first “big” project and library.

7

The thing is some of the features of mylib.a must uses features from libB.a.

Maybe I’m doing this wrong, it’s my first “big” project and library.