make cannot find the Protobuf include headers

poldi · December 22, 2023, 2:47am

I’m trying to get a tiny test with Protobuf to compile and cannot figure out why this fails. I tried to upload the code, but don’t have the rights, so bear with me when I add the code to this post.

I have the Protobuf source in the subfolder “proto”

The root has the following CMakeLists.txt

cmake_minimum_required(VERSION 3.14)

project(MyProtoBuffTest LANGUAGES CXX)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Core)

ADD_SUBDIRECTORY(proto)

include_directories(${Protobuf_INCLUDE_DIRS})

add_executable(MyProtoBuffTest
  main.cpp
)
target_link_libraries(MyProtoBuffTest Qt${QT_VERSION_MAJOR}::Core)

include(GNUInstallDirs)
install(TARGETS MyProtoBuffTest
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

The CMakeLists.txt in the proto subfolder looks like this. Please ignore my ‘debug’

FIND_PACKAGE(Protobuf REQUIRED)
PROTOBUF_GENERATE_CPP(PROTO_SRC PROTO_HEADER message.proto)
ADD_LIBRARY(proto ${PROTO_HEADER} ${PROTO_SRC})

#PROTOBUF_GENERATE_CPP(PROTO_SRC PROTO_HEADER message.proto)
#ADD_LIBRARY(proto ${PROTO_HEADER} ${PROTO_SRC})
#include_directories(${CMAKE_BINARY_DIR}/proto)

message("   --> PROTOBUF LIB: ${PROTOBUF_LIBRARIES}")
message("   --> PROTOBUF INCLUDE: ${Protobuf_INCLUDE_DIRS}")
message("   --> PROTOBUF VERSION: ${Protobuf_VERSION}")
message("   --> PROTOBUF Found: ${Protobuf_FOUND}")
message("   --> PROTOBUF SRC: ${PROTO_SRC}")
message("   --> PROTOBUF HEADER: ${PROTO_HEADER}")
message("   --> PROTOBUF Folder: ${CMAKE_BINARY_DIR}/proto")


include_directories(${CMAKE_CURRENT_BINARY_DIR})

get_property(dirs DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY INCLUDE_DIRECTORIES)
foreach(dir ${dirs})
  message(STATUS "directory is ='${dir}'")
endforeach()

The cmake output is as follows

-- The CXX compiler identification is GNU 11.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Performing Test HAVE_STDATOMIC
-- Performing Test HAVE_STDATOMIC - Success
-- Found WrapAtomic: TRUE  
-- Found Protobuf: /usr/lib/x86_64-linux-gnu/libprotobuf.so (found version "3.12.4") 
   --> PROTOBUF LIB: /usr/lib/x86_64-linux-gnu/libprotobuf.so
   --> PROTOBUF INCLUDE: /usr/include
   --> PROTOBUF VERSION: 3.12.4
   --> PROTOBUF Found: TRUE
   --> PROTOBUF SRC: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.cc
   --> PROTOBUF HEADER: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.h
   --> PROTOBUF Folder: /home/llist/QtProjects/MyProtoBuffTest/build/proto
-- directory is ='/home/llist/QtProjects/MyProtoBuffTest/build/proto'
-- Configuring done
-- Generating done
-- Build files have been written to: /home/llist/QtProjects/MyProtoBuffTest/build

the make output is

[ 10%] Automatic MOC and UIC for target MyProtoBuffTest
[ 10%] Built target MyProtoBuffTest_autogen
[ 20%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/MyProtoBuffTest_autogen/mocs_compilation.cpp.o
[ 30%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/main.cpp.o
/home/llist/QtProjects/MyProtoBuffTest/main.cpp:2:10: fatal error: proto/message.pb.h: No such file or directory
    2 | #include "proto/message.pb.h"
      |          ^~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/MyProtoBuffTest.dir/build.make:90: CMakeFiles/MyProtoBuffTest.dir/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:102: CMakeFiles/MyProtoBuffTest.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

The “proto/message.pb.h” file did get generated by cmake, but I’d appreciate if somebody could point out why the compiler can’t find it.

ben.boeckel · December 22, 2023, 1:38pm

include_directories only affects targets made after it was called. Swap the order of these two.

poldi · December 22, 2023, 11:33pm

Thanks Ben.
Have made the suggested change, but still no success.
I removed the include for the protobuf generated header and just ran the generation of the protobuf files and noticed

${Protobuf_INCLUDE_DIRS} still points to “/usr/include”. Is this something I need to specify?

llist@poldis:~/QtProjects/MyProtoBuffTest/build$ cmake ..
-- The CXX compiler identification is GNU 11.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Performing Test HAVE_STDATOMIC
-- Performing Test HAVE_STDATOMIC - Success
-- Found WrapAtomic: TRUE  
-- Found Protobuf: /usr/lib/x86_64-linux-gnu/libprotobuf.so (found version "3.12.4") 
   --> PROTOBUF LIB: /usr/lib/x86_64-linux-gnu/libprotobuf.so
   --> PROTOBUF INCLUDE: /usr/include
   --> PROTOBUF VERSION: 3.12.4
   --> PROTOBUF Found: TRUE
   --> PROTOBUF SRC: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.cc
   --> PROTOBUF HEADER: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.h
   --> PROTOBUF Folder: /home/llist/QtProjects/MyProtoBuffTest/build/proto
  This is where the include directories should be listed
-- Configuring done
-- Generating done
-- Build files have been written to: /home/llist/QtProjects/MyProtoBuffTest/build
llist@poldis:~/QtProjects/MyProtoBuffTest/build$ make
[ 10%] Automatic MOC and UIC for target MyProtoBuffTest
[ 10%] Built target MyProtoBuffTest_autogen
[ 20%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/MyProtoBuffTest_autogen/mocs_compilation.cpp.o
[ 30%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/main.cpp.o
[ 40%] Linking CXX executable MyProtoBuffTest
[ 40%] Built target MyProtoBuffTest
[ 50%] Running cpp protocol buffer compiler on message.proto
[ 60%] Automatic MOC and UIC for target proto
[ 60%] Built target proto_autogen
[ 70%] Building CXX object proto/CMakeFiles/proto.dir/proto_autogen/mocs_compilation.cpp.o
[ 80%] Building CXX object proto/CMakeFiles/proto.dir/message.pb.cc.o
[ 90%] Linking CXX static library libproto.a
[100%] Built target proto
llist@poldis:~/QtProjects/MyProtoBuffTest/build$

ben.boeckel · December 24, 2023, 1:28am

That looks like it works to me…what isn’t working here? Your protobuf install is under /usr, so the variable value makes sense to me.

poldi · December 24, 2023, 1:34am

Sorry, I should have made this clearer.
I thought/expected the “Protobuf_INCLUDE_DIRS” to point to the location of the generated headers as my real issue is that these headers are not found (as in the output of the first post).

poldi · December 24, 2023, 5:21am

I think I found the reason for the make not finding the headers generated by protobuf_generate_cpp.
I’ve added another class to the proto folder and after the build I can include that header file without any issues.
The reason is/seems to be that the new class files are under the initial src folder, while the class generated by protobuf_generate_cpp ends up under the build folder.

ben.boeckel · December 26, 2023, 2:27pm

Yes, code generation should write to the build tree rather than the source tree (so that multiple builds of the same source do not overlap).

poldi · December 26, 2023, 9:25pm

Thanks.
So what variable should I set so the compiler finds the gernerated files?

ben.boeckel · December 26, 2023, 9:29pm

You don’t set a variable, but instead pass the path (usually something based on CMAKE_CURRENT_BINARY_DIR) as an include path:

target_include_directories(with_protobuf_srcs PRIVATE "${CMAKE_CURRENT_BINARY_DIR}/subdir")

There might not be a subdir. Ideally, generate_protobuf would given such information returned in a variable, but that looks like a feature request (to protobuf upstream itself) at the moment.

poldi · December 30, 2023, 2:15am

My two CMake files look like this

cmake_minimum_required(VERSION 3.14)

project(MyProtoBuffTest LANGUAGES CXX)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Core)

add_subdirectory(proto)

add_executable(MyProtoBuffTest
  main.cpp
#  test2.h test2.cpp
)
target_link_libraries(MyProtoBuffTest Qt${QT_VERSION_MAJOR}::Core)

include(GNUInstallDirs)
install(TARGETS MyProtoBuffTest
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

get_property(dirs DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY TARGET_INCLUDE_DIRECTORIES)
message("  This is where the root directories should be listed")
foreach(dir ${dirs})
  message(STATUS "root directory is ='${dir}'")
endforeach()

INCLUDE(FindProtobuf)
FIND_PACKAGE(Protobuf REQUIRED)
protobuf_generate_cpp(PROTO_SRC PROTO_HEADER message.proto)
ADD_LIBRARY(proto ${PROTO_HEADER} ${PROTO_SRC}
    test1.h test1.cpp
)
target_include_directories(proto PRIVATE "${CMAKE_CURRENT_BINARY_DIR}/proto")

# target_include_directories(proto PUBLIC ${CMAKE_BINARY_DIR}/proto)

message("   --> PROTOBUF LIB: ${PROTOBUF_LIBRARIES}")
message("   --> PROTOBUF INCLUDE: ${Protobuf_INCLUDE_DIRS}")
message("   --> PROTOBUF VERSION: ${Protobuf_VERSION}")
message("   --> PROTOBUF Found: ${Protobuf_FOUND}")
message("   --> PROTOBUF SRC: ${PROTO_SRC}")
message("   --> PROTOBUF HEADER: ${PROTO_HEADER}")
message("   --> PROTOBUF Folder: ${CMAKE_BINARY_DIR}/proto")

get_property(dirs DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY TARGET_INCLUDE_DIRECTORIES)
message("  This is where the proto directories should be listed")
foreach(dir ${dirs})
  message(STATUS "proto directory is ='${dir}'")
endforeach()

Output form cmake and make is as follows

llist@poldis:~/QtProjects/MyProtoBuffTest/build$ cmake ..
-- The CXX compiler identification is GNU 11.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Performing Test HAVE_STDATOMIC
-- Performing Test HAVE_STDATOMIC - Success
-- Found WrapAtomic: TRUE  
-- Found Protobuf: /usr/lib/x86_64-linux-gnu/libprotobuf.so (found version "3.12.4") 
   --> PROTOBUF LIB: /usr/lib/x86_64-linux-gnu/libprotobuf.so
   --> PROTOBUF INCLUDE: /usr/include
   --> PROTOBUF VERSION: 3.12.4
   --> PROTOBUF Found: TRUE
   --> PROTOBUF SRC: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.cc
   --> PROTOBUF HEADER: /home/llist/QtProjects/MyProtoBuffTest/build/proto/message.pb.h
   --> PROTOBUF Folder: /home/llist/QtProjects/MyProtoBuffTest/build/proto
  This is where the proto directories should be listed
  This is where the root directories should be listed
-- Configuring done
-- Generating done
-- Build files have been written to: /home/llist/QtProjects/MyProtoBuffTest/build
llist@poldis:~/QtProjects/MyProtoBuffTest/build$ make
[  9%] Automatic MOC and UIC for target MyProtoBuffTest
[  9%] Built target MyProtoBuffTest_autogen
[ 18%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/MyProtoBuffTest_autogen/mocs_compilation.cpp.o
[ 27%] Building CXX object CMakeFiles/MyProtoBuffTest.dir/main.cpp.o
/home/llist/QtProjects/MyProtoBuffTest/main.cpp:3:10: fatal error: proto/message.pb.h: No such file or directory
    3 | #include "proto/message.pb.h"
      |          ^~~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/MyProtoBuffTest.dir/build.make:90: CMakeFiles/MyProtoBuffTest.dir/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:102: CMakeFiles/MyProtoBuffTest.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

ben.boeckel · January 11, 2024, 2:10pm

poldi:

/home/llist/QtProjects/MyProtoBuffTest/main.cpp:3:10: fatal error: proto/message.pb.h: No such file or directory
    3 | #include "proto/message.pb.h"
      |          ^~~~~~~~~~~~~~~~~~~~

You need to target_include_directories(MyProtoBuffTest PRIVATE "${CMAKE_CURRENT_BINARY_DIR}") to do this. It’d be better as part of the proto target’s INTERFACE, but that weirdly wants ${CMAKE_CURRENT_BINARY_DIRECTORY}/.. from its point of view.

poldi · January 13, 2024, 1:36am

I’ve added
target_include_directories(MyProtoBuffTest PRIVATE “${CMAKE_CURRENT_BINARY_DIR}”)
to the Root CMakeLists.txt; the error persists.

Thanks,
Leo

ben.boeckel · January 13, 2024, 10:33am

Is "${CMAKE_CURRENT_BINARY_DIR}" not this path in that context?

poldi · January 13, 2024, 11:13pm

I now have

target_include_directories(MyProtoBuffTest PRIVATE "${CMAKE_CURRENT_BINARY_DIR}")

in the root CMakeLists.txt and

target_include_directories(proto PRIVATE ${CMAKE_CURRENT_BINARY_DIR})

in the subfolder that creates the files from the proto definition.

It now all works

Thanks for your help
Leo