Visual studio 2015 openmp support

Question

I'm having trouble getting OpenMP support in Visual Studio 2015.

I've configured the project options to use /openmp (project->properties->C/C++->language->OpenMP support:yes), the code is as follows (very simple code, to test OpenMP):

#include <iostream>
#include <omp.h>

int main(int argc, char* argv[])
{
    int n = 0;

#pragma omp parallel
    {
        std::cout << std::endl << "Hello World!";
    }
    return 0;
}

Only one thread runs and "Hello World!" is printed only once.

Answer 1

I was able to compile the program with VS2015 Community Version 14.0 Update 1 on Windows 8.1 64bit with OpenMP support.

Below, follow a list of steps that may help:

• After create a new project and paste the source code, go to

Project-> Properties -> C/C++ -> Language

Change Open MP Support to Yes(/openmp)

Click Apply

• On the left menu, go to Command Line and confirm that /openmp appears somewhere at the compiler's options.

If it appears, click Ok and build the project.

---

Before run the program, put a breakpoint at the line:

int n = 0;

Run the the program by clicking on Local Windows Debugger

When the program stops at the breakpoint, go to Debug -> Windows -> Disassembly

Somewhere, near the breakpoint, look for an assembly line like:

call __vcomp_fork (?????????h)

If you find this line, chances are that openmp is ok and running.

---

Some other checks that can help:

Get a tool from Windows Sysinternals like Process Explorer (GUI) or ListDLLs (command line).

ListDLLs:

With the program stopped at the breakpoint, open task manager and look for the PID of the process.

Open a command prompt and run the command:

listdlls [PID] | findstr -i vcomp

Should appear something like VCOMP140D.DLL or VCOMP140.DLL or VCOMP????.DLL.

If it not appears, probably the compiler couldn't find the openmp dll so you'll have to see if this library is available at some point on your system.

---

Two last tips that may save your time:

If you change any configuration (e.g. Debug -> Release or x86 -> x64), check again if Command Line has the /openmp option set ok.

If you try to force the compiler to C language (instead of C++), maybe the pragma:

#pragma omp parallel for

will not work (Update: Apparently this problem does not happen anymore on VS2017).

It shows me the message:

INTERNAL COMPILER ERROR in 'C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin\CL.exe'

Come back the compiler to C++ language and the parallel for will works ok.

Answer 2

Partial answer: I was not able to get the compiler to accept /openmp through the config/GUI, but compiling in console with cl.exe /openmp works.