VS Code doesn't find my #include files - tried all possible ways - c++

Question

I know that this issue has been raised several times, but even trying all possible suggestions I could find on the Internet, I couldn't find a way to make my simple program work.
Here is the story: I am starting a C++ program with Visual Studio Code, and I want to use the openCV libraries. Since I'm a beginner at these things, I started by cutting & pasting some simple program from an opencv tutorial. When I try to build, VSC doesn't find the openCV files and throw an error.
C:\Users\Roberto\Documents\Program Data Files\C++\SVM\Test1.cpp:5:10:
fatal error: opencv2/core.hpp: No such file or directory #include
<opencv2/core.hpp>
The program starts with these #include (none of the opencv2 files is found):
#include <iostream>
#include <string>
#include <iomanip>
#include <sstream>
#include <opencv2/core.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>
This is my launch.json:
"version": "0.2.0",
"configurations": [
{
"name": "Debug",
"type": "cppdbg",
"request": "launch",
"program": "${fileDirname}\\${fileBasenameNoExtension}.exe",
"args": [],
"MIMode": "gdb",
"miDebuggerPath": "C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/gdb.exe",
"stopAtEntry": true,
"cwd": "${workspaceFolder}",
"environment": [],
"externalConsole": false
}
]
This is c_cpp_properties.json
{
"configurations": [
{
"name": "Win32",
"includePath": [
"C:/Users/Roberto/Documents/Program Data Files/C++/opencv/build/include/*",
"${workspaceFolder}/**"
],
"defines": [
"_DEBUG",
"UNICODE",
"_UNICODE"
],
"windowsSdkVersion": "10.0.17763.0",
"compilerPath": "C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/g++.exe",
"cStandard": "c11",
"cppStandard": "c++17",
"intelliSenseMode": "gcc-x86"
}
],
"version": 4
}
The idea is that the openCV files are in the directory in the includePath.
I have read in several places that I shouldn't use includePath but only compilePath. Now, I'm not sure what it means, but I also tried to copy the entire folder of the openCV include files in the coplier directory, but with no success.
A couple of notes. Intellisense "finds" the files, because if I start typing "#include <op..." it immediately suggests me the opencv2 folder, and after that the core.hpp etc... And, of course, the files ARE in the right directory.
I also tried to bypass this problem by adding the -I instruction in the task.json:
{
"version": "2.0.0",
"tasks": [
{
"type": "shell",
"label": "C/C++: g++.exe build active file",
"command": "C:\\Program Files\\mingw-w64\\x86_64-8.1.0-posix-seh-rt_v6-rev0\\mingw64\\bin\\g++.exe",
"args": [
"-g",
"${file}",
"-o",
"${fileDirname}\\${fileBasenameNoExtension}.exe",
"-IC:/Users/Roberto/Documents/Program Data Files/C++/opencv/build/include"
],
"options": {
"cwd": "${workspaceFolder}"
},
"problemMatcher": [
"$gcc"
],
"group": {
"kind": "build",
"isDefault": true
}
}
]
}
In this case, I get a different error, i.e., all openCV functions calls are flagged as "undefined reference to cv::...'
Any suggestion on how to make this thing work?

Answer 1

After many trials, I came up with some explanation and solution, in case anybody else has the same problem.
Recap: my problems where:
find the header files listed as #include
link the proper opencv library
For 1), it seems that using the "includePath" setting available in the c_cpp_properties.json DOES NOT do what anyone would logically expect (in fact, I don't know if it is used at all). The only way I found was to specify an Include path is to explicitly use the argument "/I" in the tasks.json
For 2), first I found somewhere someone claiming that VS Code has to use the Microsoft C++ compiler, and is not compatible with mingw. I am pretty sure it is not the case, but I decided nevertheless to switch to Microsoft's cl.exe
Second, it seems that to make VS Code "find" the compiler you need to have some specific environmental variable set. I didn't found out exactly which variable, but the trick is to:
a) launch the "x64 Native Tool Command Prompt for VS2019". This opens a cmd window and executes a number of variable settings and other stuff. This file can be obtained from the download page (https://visualstudio.microsoft.com/downloads/) of Visual Studio, going to the bottom to "Tools for Visual Studio 2019" and then "Build Tools for Visual Studio 2019"
b) from this command prompt, navigate to your working directory, and from there launch the instruction "code .", which, assuming the path to your VS Code installation is in the PATH variable, will launch VS Code
c) if I instead launch VS Code directly from window, it won't work (doesn't find cl.exe)
Third, there are different cl.exe, depending on whether one is compiling from a 32 or 64 bit platform onto a 32 or 64 bit target ... I wasted some tie figuring out this, and the key is using the correct "x64 Native Tool Command Prompt for VS2019"
Fourth, the opencv library has to just be listed in tasks.json preferably AFTER all other arguments (if I remember correctly, I got a mistake earlier because I called it before the actual file being compiled)
It is perfectly possible that alle these problems above were only specific to my PC, or to the fact that I am yet a very beginner with this stuff ... but if not, glad if my experience might of any help

Answer 2

"undefine reference to cv ..." it means that the linker could not find the functions you are calling in your code. Make sure you link the libraries properly.