C Compilation Fails in Visual Studio Code-CodePudding

EDIT

As pointed out in the comments, the issue is actually unrelated to OMP. The compilation failed because the -lm argument was missing in tasks.json. It is therefore unrelated to OMP.

Original Question

I have a *.c file (written in C) that uses omp_get_wtime(). Therefore, I have #include <omp.h> in the preamble. Compiling with gcc -o test test.c -Ofast -lm -fopenmp works. But hitting the 'Debug' button in Visual Studio Code (I'm on Linux) does not build successfully:

 *  Executing task: C/C  : gcc build active file 

Starting build...
/usr/bin/gcc -fdiagnostics-color=always -fopenmp -g
/home/[...]/test.c -o /home/[...]/test
/usr/bin/ld: /tmp/ccsQiVzo.o: in function `main':
/home/[...]/test.c:89: undefined reference to `sqrt'
collect2: error: ld returned 1 exit status

Build finished with error(s).

 *  The terminal process failed to launch (exit code: -1). 
 *  Terminal will be reused by tasks, press any key to close it.

(#include <math.h> is there, so it should know sqrt)

How do I configure VSCode such that it succesfully compiles C code with gcc and OpenMP?

Thank you so much in advance for your help!

I specified the tasks.json to use -fopenmp:

{
    "tasks": [
        {
            "type": "cppbuild",
            "label": "C/C  : gcc build active file",
            "command": "/usr/bin/gcc",
            "args": [
                "-fdiagnostics-color=always",
                "-fopenmp",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}"
            ],
            "options": {
                "cwd": "${fileDirname}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "Task generated by Debugger."
        }
    ],
    "version": "2.0.0"
}

My c_cpp_properties.json looks as follows:

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**",
                "/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.0/include/"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "c17",
            "cppStandard": "c  14",
            "intelliSenseMode": "linux-gcc-x64"
        }
    ],
    "version": 4
}

The launch.json is empty:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": []
}

CodePudding user response：

The error is from /usr/bin/ld which is the linker, not the compiler. This means that 1. by including the math.h header the compiler succeeded, but 2. the linker is missing a library with the definition of your sqrt function.

Try adding -lm to the link line, which supplies the math library. Quite often the compiler adds that one on its own, but apparently not in this case.