We are using an environment variable to specify a path to a library we use. Most of the time it points to the released version but sometimes to a development version.
Anyway, it works ok when I use $(MyLib)/path;%(AdditionalIncludeDirectories) for building the C++ application but I can not open the project resources. However, when I use %(MyLib)/path;%(AdditionalIncludeDirectories) it works.
Now, what is the difference?
I thought the correct way is to use $(EnvVar) but for the resource editor it doesn't seems to work. And if $(EnvVar) is the correct way then why does Visual Studio use %(AdditionalIncludeDirectories) and not $(AdditionalIncludeDirectories)
The error I get is: fatal error RC1015: cannot open include file 'afxres.h'.
You use %(item) to refer to an MSBuild metadata item. Using $(AdditionalIncludeDirectories) would not work well if you also had an environment variable by that name. So %(MyLib)/path ought to resolve to just /path.
You can put echo %(MyLib)/path in a prebuild event to verify this.
Which is probably enough to stop confusing rc.exe, the resource compiler. Which is a stone-cold-old SDK utility, going back all the way to Windows version 1.0. It is pretty temperamental, very picky about command line options and .rc script file text encoding. Do keep in mind that it dates from an era long before Windows started to support a forward slash as a path separator, everybody had to use a backslash back in 1986.
So use "$(MyLib)\path" instead, including the double quotes so you don't confuzzle it when MyLib contains embedded spaces. And do favor using a project property sheet instead so there are some odds that somebody can still figure out how to get the project built correctly 2+ years from now.