Fetch specific errors in MMG

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#1

Hello there. First of all, thank you for this very useful library.
I’m using it for meshing 2d elements and I stumbled into a problem. Sometimes I’m passing data to MMG2D which are non-consistent, I mean numerically wrong.
Those are some very limited side cases, which happens when my meshes are very tiny, i.e. very little verts and edges lengths. The tool I use before calling MMG seem to have a bug, and generates those inconsistent results which are then fed to MMG.
Thus I get:

Error: MMG5_boundingBox: unable to scale mesh: Check that your mesh contains non-zero points and valid elements.
Assertion failed: ((dataPtr == 0) || ( rows >= 0 && (RowsAtCompileTime == Dynamic || RowsAtCompileTime == rows) && cols >= 0 && (ColsAtCompileTime == Dynamic || ColsAtCompileTime == cols))), function MapBase, file /Users/Developer/eigen/Eigen/src/Core/MapBase.h, line 176.

which is in turn generated by the bbox code check in mmg/src/common/scalem.c,
int MMG5_boundingBox(MMG5_pMesh mesh), about line 70

  mesh->info.delta = 0.0;
  for (i=0; i<mesh->dim; i++) {
    dd = mesh->info.max[i] - mesh->info.min[i];
    if ( dd > mesh->info.delta )  mesh->info.delta = dd;
  }
  if ( mesh->info.delta < MMG5_EPSD ) {
    fprintf(stderr,"\n  ## Error: %s: unable to scale mesh:"
            " Check that your mesh contains non-zero points and "
            "valid elements.\n",__func__);
    return 0;
  }

called by MMG2D_mmg2dmesh in my code.
Of course I could trap the numerical errors by some isFinite check in Eigen, but I’d like to know if there’s a way to fetch this specific error in some way. Apparently the meshing call only returns MMG5_STRONGFAILURE, MMG5_LOWFAILURE…
Basically my question is if it’s possible to fetch a specific error in MMG.
Thank you in advance

#2

Hello,

Thank you for using Mmg!

I think that it should be possible to play with stream redirection to redirect error messages in file and then parse this file to find a given error message. See for example the following links:

Do not hesitate to post a minimal code of your solution if it works, it can interest other users!

Best Regards,

Algiane

#3

yes, actually is possible to fetch the stderrr. I have used

which gets things easier. Here it is:

main.cpp

#include <subprocess.hpp>

#include <filesystem>

#include <iostream>

auto subprocrun = [&](
                      std::vector<std::string> &params,
                      int &rc,
                      std::string &out,
                      std::string &err) -> bool
{
    using namespace std;
    using subprocess::CompletedProcess;
    using subprocess::PipeOption;
    using subprocess::RunBuilder;

    CompletedProcess process = {};

    // capture output with exceptions
    try
    {
        process = subprocess::run(
            {params}, RunBuilder().cerr(PipeOption::pipe).cout(PipeOption::pipe));
    }
    // command not found
    catch (const std::exception &e)
    {
        cout << "Cannot Run!" << endl;
        return false;
    }

    return true;
};

auto findstr = [](std::string item, std::string search) -> int
{
    std::size_t found = item.find(search);
    if (found == std::string::npos)
        return -1;

    return found;
};

int main(int argc, char *argv[])
{
    using namespace std;

    std::vector<std::string> params = {};
    std::string out, err = {};
    int rc = {};

    std::string mmg_exe = "your_path_to_mmg.exe";
    std::string mmg_data = "your_path_to_mmg_data_file";
    std::string mmg_param1 = "your_mmg_option1";
    std::string mmg_param2 = "your_mmg_option2";

    params.push_back({mmg_exe});
    params.push_back({mmg_data});
    params.push_back({mmg_param1});
    params.push_back({mmg_param2});
    // and so on

    if (!subprocrun(params, rc, out, err))
    {
        cout << "Cannot Run!" << endl;
        return EXIT_FAILURE;
    }

    // show output
    cout << "MMG called with reply:\n"
         << out << endl;

    // check result
    if (rc != 0)
    {
        cout << "MMG Error!" << endl;

        // check stderr
        if (err.size())
        {
            // check specific MMG error
            if (err.size())
            {
                //
                // YOUR MMG STRING ERROR TO CHECK
                //
                std::string MMG_STDERR = "unable to scale mesh";

                if (findstr(err, MMG_STDERR) > 0)
                {
                    cout << "MMG Error: " << MMG_STDERR << endl;
                    // DO YOUR LOGIC
                    return EXIT_FAILURE;
                }
            }
        }
    }

    return EXIT_SUCCESS;
};

Anyway, I’d like to fetch the error using a direct call… but this is not possible short of directly rewriting MMG error management in the library itself…
Thank you

#4

Hi,

Great, thanks for the feedback.

Indeed, it is complicated to change the handling of errors of the library directly because it impacts existing interfacing.

Sorry for that,

Have a nice day,