问题
What does this red minus flag mean in visual studio?
回答1:
I believe this means the file is excluded from the build.
Note that this seems to be a bit different from "Exclude from project", in that the file shows up in the listing, but if you right-click on it and look at Properties > General, Exclude from build is set to Yes. If you set it to No, the red minus goes away.
One more datapoint, the project I imported started out as a VC6 project so this might be Visual Studio 2010's way of representing a legacy setting that was different than Exclude from Project.
The other comment about it indicating a missing item shows an exclamation point icon, not a minus.
回答2:
Red circle icon with white minus means that file is excluded from source code control. Right click on filter "Header files" for example and find out how "SCC Files" property is set. Probably is set to false, change it to true and icon will disappear.
来源：https://stackoverflow.com/questions/12259323/what-does-this-red-minus-overlay-icon-mean-in-visual-studios-solution-explorer