Mac Excel VBA dylib (gfortran based) file operations fail

Question

I am porting a VBA and an associated dylib program from Windows Excel 2010/2014 to Mac Excel 2010. Before it performs an operation, the VBA changes the current working directory to the installation folder, to make the input files available to the DLL.

The dylib is based on gfortran 4.9.0. I put the dylib file in the ~/lib folder, and VBA can locate it, use it to perform calculations and return results.

However, when I try to perform any disk operations (getcwd, open), an error is thrown. I can return the error (13), which appears to be "permission denied" according to "/usr/include/sys/errno.h".

I am able to place a gfortran dll in ~/lib, and have another fortran program call it successfully (from the command prompt, not within Excel) and write a file in the current working directory, so it seems like it ought to work.

Any thoughts on who "owns" the spawned dylib processes and how to perform disk operations by a gfortran dylib from a VBA call would be appreciated.

Answer 1

It turns out that on the Mac when calling a dylib (at least a gfortran dylib) from Excel 2011, the dylib's cwd is the root / folder on a Mac. This differs from Windows, in which the dll's cwd is the user's cwd. So while on Windows vba, you can change the cwd in Excel and assume the dll will also have it by default, but on a Mac the dylib itself would need to do a CHDIR itself each time it is called from VBA (it resets and doesn't remember where it set itself to previously).

Also note that StrConv does work under Mac 2011, at least to change to the string to single byte characters, but the latter half of the string that was previously used to help with the unicode may not be translated correctly if you have fixed length strings. Using an extra long fixed length string can account for that:

Function StrConv2(s as string, coding as integer) as String
' used to convert fixed length strings between unicode and ascii for Mac
' (not needed for Windows)
  Dim s2 as string*2048 ' at least twice as long as your original string
  If coding = vbUnicode Then
    StrConv2 = StrConv(s, coding)
  Else
    s2 = s
    StrConv2 = StrConv(s2, coding)
    s = s2
  End If
End Function