find_package failed to generate project (in Qt) with Cmake

Question

I’m trying to generate the build configuration of a simple Qt example using Cmake. The code of the example is this:

#include <QApplication>
#include <QTextEdit>

int main(int argc, char** argv)
{
    QApplication app(argc, argv);

    QTextEdit textEdit;
    textEdit.setText("Olá mundo!");
    textEdit.show();

    return app.exec();
}

And the Cmake configuration file is this:

cmake_minimum_required(VERSION 2.8.11)

project (teste)

# Configuracao do Qt
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTOMOC ON)
find_package(Qt5Core)
find_package(Qt5Widgets)

# Configuracao especifica para o gcc
if(NOT WIN32)
    set(CMAKE_C_FLAGS "-Wall -g")
endif()

# Adiciona todos os fontes na variavel SRCS
file(GLOB SRCS *.cpp *.h)

# Nome do executavel
if(WIN32)
    add_executable(teste WIN32 ${SRCS})
else()
    add_executable(teste ${SRCS})
endif()

# Usa os modulos do Qt 5
target_link_libraries(teste Qt5::Core)
target_link_libraries(teste Qt5::Widgets)

When I Gero the configuration in Windows (v.10, 64bits), it goes well. However, when I do the same on Ubuntu (v.14.04, 32bits), Cmake produces the following error message:

Cmake Warning at Cmakelists.txt:8 (find_package): By not providing "Findqt5core.cmake" in CMAKE_MODULE_PATH this project has Asked Cmake to find a package Configuration file provided by "Qt5core", but Cmake Did not find one.

Could not find a package Configuration file provided by "Qt5core" with any of the following Names:

 Qt5CoreConfig.cmake
 qt5core-config.cmake

Add the installation prefix of "Qt5core" to CMAKE_PREFIX_PATH or set "Qt5core_dir" to a directory containing one of the above files. If "Qt5core" provides a Separate Development package or SDK, be sure it has been installed.

Some additional information:

• Qt 5.5.1 is correctly installed on Ubuntu (in the local folder /home/luiz/Qt5.5.1).
• Running the command apt-file search Qt5CoreConfig.cmake, i get the following path: qtbase5-dev: /usr/lib/i386-linux-gnu/cmake/Qt5Core/Qt5CoreConfig.cmake. So I’ve tried to add /usr/lib/i386-linux-gnu/cmake/ the environment variable CMAKE_PREFIX_PATH (as directed the documentation in the fifth paragraph of Getting Started), but the error continues.
• I just didn’t try to define individually the variables Qt5<Module>_DIR because I believe that this approach will only take more work than necessary (and maybe there is some other wrong configuration).

Does anyone know where I might be going wrong?

Answer 1

I managed to solve with help of that other thread. There were two problems:

1. Instead of setting the path in a variable CMAKE_PREFIX_PATH environment, it seems that the "most correct" is to do as a variable within the Cmake script.
2. The correct path is even the installation of Qt, but including the compiler specification (in the case of Ubuntu, gcc).

So I just added the following snippet to my Cmake script, before calling the find_package:

if(WIN32)
    set (CMAKE_PREFIX_PATH "C:\\Qt\\Qt5.6.0\\5.6\\msvc2015\\")
elseif(UNIX)
    set (CMAKE_PREFIX_PATH $ENV{HOME}/Qt5.5.1/5.5/gcc/)
endif()

The definition of the variable CMAKE_PREFIX_PATH was not required on my Windows environment earlier because the Qt path was added to the Path. Thus, to avoid this specific configuration within the Cmake script file, the most appropriate is to add the Qt installation path to the variable PATH environment (both on Windows and Linux) and not using the variable CMAKE_PREFIX_PATH.