how to purposely fail "fopen" for debuggin

[koopey]

I need to purposely fail the "fopen"-ing of a file to test my code. How do I do that. my code so far:

  void MeshTrian::init (std::string filename)
{
    if (!sofa::helper::system::DataRepository.findFile(filename))
    {
        msg_error() << "File '" << filename << "' not found." ;
        return;
    }
    FILE *f = fopen(filename.c_str(), "r");
    bool status;
    msg_error_when(!(status=f))<<sofa::helper::message::UnableToOpenFile(filename.c_str());
    if (status)
    {
        readTrian (f);
        fclose(f);
    }
}

[tpb]

Can you post the code for msg_error_when?

[Repeater]

In test mode, you could have TEST_MODE defined. Either in the code, or as an argument passed to the compiler.

Then something like this in the right place:

#ifdef TEST_MODE
#define fopen(x, y) nullptr;
#endif 

which would turn your fopen call into a straight nullptr value.

I've not tested this and I rarely use this kind of preprocessor macro, so it might be bad syntax; the idea should be solid.

Even something as awkward as

#ifdef TEST_MODE_FAIL_FILE_OPEN
  FILE *f = nullptr;
  #else
  FILE *f = fopen(filename.c_str(), "r");
#endif 

at line 8 would do it, although it's possible to end up getting silly with excessive preprocessor magic.

[Thomas1965]

Another option is to set filename to some non-existing file:

#ifdef TEST_MODE
  filename = "I don't exist";
#else
  filename = "Existing filename";
#endif 

[dhayden]

Change the permissions on the file so it can't be read by the program.