[VS2022] Build Succeeded but “Red Squiggles” Persist? How to Fix IntelliSense Errors

If you develop in MFC/C++, you’ve likely experienced Visual Studio “lying” to you. The code is correct, and the Build (Ctrl+Shift+B) succeeds without errors, but the editor continues to show red squiggly lines under variables or class names.

Usually, we ignore these as temporary IntelliSense glitches. However, they are visually distracting and can make it difficult to spot actual typos, so it is a problem that needs fixing.

Today, I’m sharing a clean solution for these “False Positive” errors that persisted even after trying standard fixes like rescanning the solution or deleting the .vs folder.

1. The Problem

• Environment: Visual Studio 2022, C++/MFC Project
• Symptoms:
  • Variables are declared correctly, and headers are properly included.
  • The actual build succeeds.
  • However, the code editor fails to recognize the variables and marks them with red errors.

2. Failed Attempts

• Rescan Solution
• Restart Visual Studio
• Deleting and regenerating the hidden .vs folder in the project directory
  • (Note: This usually fixes most issues, but it didn’t work in this specific case.)

3. The Solution: Explicitly Adding Include Directories

The issue was caused by the IntelliSense engine failing to properly track the relative paths of the project. The solution was to explicitly set the project’s root path as an absolute reference point.

1. Right-click the project and select [Properties].
2. Go to [Configuration Properties] -> [VC++ Directories].
3. Open the editor for [Include Directories].
4. Add a new line and enter the $(ProjectDir) macro.
   • $(ProjectDir) is a VS macro that resolves to the directory containing the project file (.vcxproj).
5. Click [Apply].

As soon as I applied this setting, the red lines disappeared, and the development environment returned to normal.

4. Root Cause Analysis

While the Compiler successfully locates files through the build tool’s complex path configurations, the IntelliSenseengine (which parses code in real-time) can sometimes lose its way.

This is especially common in complex legacy projects or secure internal network environments. IntelliSense may fail to locate header files relative to the current file. Adding $(ProjectDir) acts as a clear signpost, telling IntelliSense to “always look for headers starting from the project folder,” which resolves the ambiguity.

I hope this helps other developers who are being tortured by VS’s red lines!

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