How to add an images folder to CMake project in order to use those images in the c++ executables?

Question

I am totally new to Qt and CMake. I have been doing a google test on my project (cmake and qt) for which I need to test the match of two images. I have a folder (outside the project directory) that contains these images. I want to access these images but not using the absolute path.

Something like this:

imread("home/../../test_images/img1.jpg")

But I want to set a common path for the images folder, so that anybody using my project later on will just have to set their test_image folder path with respect to their machine, and need not make changes in the code.

I have tried the following so far.

1 . Tried adding a .qrc resource file and tried to access the images. (This did not work since the images folder was outside the project directory.)

2. Tried to set a Path variable in QT build environment settings.

None of the two methods worked.

What I am trying to accomplish: "To be able to avoid using an absolute path for the images I use and allow people trying to implement my code to only change the path at one place with their own test image locations."

Edit: Looking for a way for setting a variable eg.IMG_PATH = "/path/to/image/files" which can be set once and only the variable is used all over the executable files. So when someone clones my project they will just have to update the IMG_PATH variable with the path to where their image files are located. So that now the IMG_PATH variable gets updated everywhere in the remaining parts of the project.

UPDATE after answer given by @squareskittles :

My project Structure :

Project_Tester

|--CMakeList.txt

|--ExecutableScript.sh.in   

|--test

       |---CMakeList.txt

       |---sample1.cpp

       |---sample2.cpp

       |---main.cpp

Sample 1,2 are c++ files with different testcases. The main.cpp runs all tests in the sample.cpp files, as below :

#include "gtest/gtest.h" 

int main(int argc, char** argv)
 { 
       ::testing::InitGoogleTest(&argc, argv);

       return RUN_ALL_TESTS(); 
}

According to answer given by @squareskittles , How should i structure my main.cpp ,to be able to use/access the variable "IMAGES_PATH" in the files sample1.cpp and sample2.cpp ?

1. Is there a way to do it from QT Creator alone than running it from the terminal ?(by modifying .sh file contents)?

2. Or can the Path be set manually in the ExecutableScript.sh.in file ?

3. How can I access this variable that is set, from the other cpp files of the project ?

Answer 1

Define your pictures path in your program settings. Use the QSettings class to store (persist) and retrieve your program settings when needed. You may want to provide your uses with a QDialog to edit your program settings. Here is an example of a portable app doing that.

Answer 2

To expand my suggestion, you can use CMake to grab an initial default path from the user configuring and building the project. CMake can grab the path from the command line like this, then use configure_file() to populate an executable start script with the provided path.

Run cmake with the -D option like this to populate a CMake variable called IMAGES_PATH:

cmake -DIMAGES_PATH=/my/path/to/imagefiles ..

Add a configure_file() call to your CMakeLists.txt to generate an executable start script:

...
configure_file(
    ${CMAKE_SOURCE_DIR}/MyExecutableStartScript.sh.in 
    ${CMAKE_BINARY_DIR}/MyExecutableStartScript.sh @ONLY
)

This call reads in the template file (MyExecutableStartScript.sh.in) and will generate a new MyExecutableStartScript.sh file, replacing the @IMAGES_PATH@ variable in your template start script with the actual path to the images. The template file would look something like this:

#!/bin/sh

./MyExecutable "@IMAGES_PATH@"

The populated start script (after running CMake) would be renamed MyExecutableStartScript.sh and contain this:

#!/bin/sh

./MyExecutable "/my/path/to/imagefiles"

A simple C++ executable to read this command line path argument could look something like this:

#include <string>
#include <iostream>

int main(int argc, char ** argv) {
    string imagesPath = "";
    if( argc == 2 ) {
      imagesPath = argv[1];
    } else {
      std::cout << "Usage: ./MyExecutable /path/to/images" << std::endl;
      return 1;
    }
    ...
}

Once the executable is built, the path to your images can easily be changed by modifying the generated start script manually. Most importantly, this example allows you to set a default location once at the beginning, but you also wouldn't require a code re-build to change the image file path.