Question: I'm building some projects using cmd devenv.

For some projects I want to #define form the command line.

Is there a way to #define using the cmd and devenv? I don't want to create new configurations.

Answer: 
You could do this:

* Add `$(AdditionalPreprocessorDefinitions)` to the list of preprocessor definitions of the project. After that, they might look like `WIN32;_DEBUG;_CONSOLE;$(AdditionalPreprocessorDefinitions);%(PreprocessorDefinitions)`
* Use `msbuild` instead of `devenv` to start the build process
* Specify the additional preprocessor definitions by adding `/p:AdditionalPreprocessorDefinitions="SOMEDEF;ANOTHERDEF"` to the command line.

Please not that I picked the name *AdditionalPreprocessorDefinitions* just for clarity, you can pick something shorter. This will only work with VC2010, because in earlier versions, VC++ projects were not built with msbuild.
Many compilers allow you to set define macros at the command line. The common option is "-D". 

Check your compiler documentation for exact syntax.

Edit 1:
The Visual Studio compiler has configuration options to specify the macros in the IDE (which get passed to the compiler using the "-D" switch.)