I have a Fortran dll callable from Excel that has worked for years. I recently got upgraded to 64 bit Office and get an error that it can't find the dll. I think this is because of the conversion to 64 bit Excel that I need to recompile the dll using the 64 bit compiler. I look at the Intel folder in Program Files and, in the bin folder, there are compilers in the folders ia32, intel64, intel64_ia32, and intel64_mic. When I launch Visual Studio and start a new project, I don't see where I select which compiler I'd like to use. I've put /Qm64 in compile and link command lines, but I then get unresolved externals because the log file seems to show the 32 bit compiler still being used. How do I select the 64 bit for this project?
In Visual Studio, do you have the Fortran Project that is/was used to build the dll from the Fortran sources?
If NOT, do you have the sources such that you can create a project that builds the dll?
If you do have the project (and sources), then, depending on the version of Visual Studio, at the top of the IDE, in the tool bar, you have some pull-downs, one of them, usually the right most, is the Solution Platform. it will likely sow Win32.
Click on the pull-down. If you see x64, select that, then Build.
If you do not see x64, you may see either <new> or Configuration Manager. Click on that. Then you should get an option to Add a platform. My preference is to Copy in the settings from the current platform .AND. check the box to create new folders. After this then back out and build.
If you only have a DLL, then you will have to consult the vendor to obtain the x64 build.