[vtkusers] question about vtk error macro

[Mark Roden]

Hi all,

I'm having a problem with the vtk error macro, and was hoping someone could
shed some light on the issue.

The relevant lines for this problem start on line 467 of vtkGetSet.h from
the git head:

     vtkmsg << "ERROR: In " __FILE__ ", line " << __LINE__      \
            << "\n" << self->GetClassName() << " (" << self     \
            << "): "  x << "\n\n";                            \

If x is a std::string, the above fails to compile, but the following is
fine:

     vtkmsg << "ERROR: In " __FILE__ ", line " << __LINE__      \
            << "\n" << self->GetClassName() << " (" << self     \
            << "): " << x << "\n\n";                            \

Note the extra << right before x.

I'm doing this to debug a problem in the vtkGDCMImageReader I'm having where
images aren't being read in Java, but are read just fine in C++-- I think
that there's a problem with string termination, but I don't know.  So, I
want to add the filename to the debug message.

The lines in gdcm are:

  if( !reader.Read() )
    {
      //added more detail for those instances where you can't debug, like in
java
      std::string theFilename(filename);
      std::string theError = "ImageReader failed on file: " + theFilename;
      vtkErrorMacro( theError );
      return 0;
    }

and they were:

  if( !reader.Read() )
    {
      vtkErrorMacro( "ImageReader failed" );
      return 0;
    }

I don't want to change vtk at all, I want to use what exists.  I could just
modify my version right now to make my error message work (or at least
compile)-- but how should I use the warning/error macros to get more
information out than just a pure const char*?  I tried to use
theError.c_str(), but that also failed.  It also failed to compile if I just
sent filename over directly, as in vtkErrorMacro(filename);

Thanks,
Mark
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