Cannot Open .png file with CImg on CLion (macOS) - c++

Question

I've tried including libpng16/png.h and #define cimg_use_png, but none of them solved the error. Also, I have main.cpp, lenna.jpg and CImg.h in the same directory.
CMakeLists.txt:
cmake_minimum_required(VERSION 3.6)
project(HelloWorld)
set(CMAKE_CXX_STANDARD 17)
set(SOURCE_FILES main.cpp)
add_executable(HelloWorld ${SOURCE_FILES})
set(YOU_NEED_X11 1)
set(YOU_NEED_PNG 1)
if (${YOU_NEED_PNG} EQUAL 1)
message(STATUS "Looking for libpng...")
find_package(PNG REQUIRED)
include_directories(${PNG_INCLUDE_DIR})
target_link_libraries (HelloWorld ${PNG_LIBRARY})
target_compile_definitions(HelloWorld PRIVATE cimg_use_png=1)
endif()
if (${YOU_NEED_X11} EQUAL 1)
message(STATUS "Looking for X11...")
find_package(X11 REQUIRED)
include_directories(${X11_INCLUDE_DIR})
target_link_libraries(HelloWorld ${X11_LIBRARIES})
else()
target_compile_definitions(HelloWorld PRIVATE cimg_display=0)
endif()
main.cpp:
#include <iostream>
#include "CImg.h"
using namespace cimg_library;
int main() {
CImg<unsigned char> img("lenna.png");
int h = img.height();
int w = img.width();
int s = img.spectrum();
std::cout << "h: " << h << " w: " << w << " s: " << s << std::endl;
return 0;
}
The error:
[CImg] *** CImgIOException *** [instance(0,0,0,0,0x0,non-shared)] CImg<unsigned char>::load(): Failed to open file 'lenna.png'.
libc++abi.dylib: terminating with uncaught exception of type cimg_library::CImgIOException: [instance(0,0,0,0,0x0,non-shared)] CImg<unsigned char>::load(): Failed to open file 'lenna.png'.
Process finished with exit code 6

Answer 1

It looks like lenna.png is not being found. Relative paths are relative to the directory containing the executable. That means that if the executable is at cmake-build-debug/HelloWorld and you try to open lenna.png, the file at cmake-build-debug/lenna.png is opened. This means that you should either manually copy lenna.png into cmake-build-debug (I don't recommend this) or ask CMake to do it for you.
Add this to your CMakeLists.txt file.
add_custom_command(
TARGET HelloWorld POST_BUILD
COMMAND ${CMAKE_COMMAND} -E copy
${CMAKE_SOURCE_DIR}/lenna.png
${CMAKE_BINARY_DIR}/lenna.png
)
This will cause lenna.png to be copied into the same directory as your executable every time the executable is compiled.