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StanDarsh18
StanDarsh18

Reputation: 33

How do I conditionally compile c++ source files in Visual Studio 2019?

I need to conditionally compile C++ source files based on either environment variables or other input parameters. Is there a mechanism in VS2019 to do this?

Upvotes: 3

Views: 1863

Answers (2)

SoronelHaetir
SoronelHaetir

Reputation: 15172

This can actually be accomplished directly by editing the project's .vcxproj file by adding a "Condition" attribute to the CLCompile element for the file in question.

Note that if you do add a Condition attribute then change the properties specifically for that file VS may remove the attribute (I am not sure whether VS does so or not, but it is something to keep in mind).

Upvotes: 1

François Andrieux
François Andrieux

Reputation: 29072

This solution works with VS2017 but I don't know of any reason why it wouldn't also work with VS2019.

You can "import" environment variables as preprocessor definitions. In your Visual Studio project's properties go to Configuration Properties -> C/C++ -> Preprocessor. Click in the Preprocessor Definitions field, hit the down arrow at the far right and select Edit.

Here, you can add preprocessor definitions that include environment variables. Each line represents a definition with the notation [name]=[value] which defines a preprocessor definition named [name] which will be substituted by [value]. Environment variables should be wrapped in a $() to be resolved. So, for example, to import the environment variable MY_ENV_VAR you would add the definition MY_ENV_VAR=$(MY_ENV_VAR). If MY_ENV_VAR had say 5 at the time of compilation, this definition would be equivalent to having a #define MY_ENV_VAR 5 available across the project.

In your source file, you can then wrap your code with a #if/#endif guard to conditionally compile that code. Using the same example, to only compile a source file if MY_ENV_VAR is exactly 1, you would write :

#if MY_ENV_VAR == 1

// Entire source file

#endif  // #if MY_ENV_VAR == 1

Note that environment variables are loaded when Visual Studio launches. You may need to restart Visual Studio if you want recent changes to the environment variables to be visible.

Upvotes: 3

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