Visual Studio displaying errors even if projects build

Question

I have a problem with Visual Studio on a C  solution  It displays totally random errors  but the projects build  Right now  I have 33 files with errors  and I can see red squiggly lines in all of them  I tried cleaning   rebuilding the solution  closing Visual Studio and even restarting my computer  I can modify  cs files and I see the changes in the solution  Does anyone have an idea about why it does that

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TL DR  Perform a clean re-install of Visual Studio  After wasting several hours  I still couldn t fix it for Visual Studio 2017  I then installed Visual Studio 2019 PREVIEW and all of a sudden  IntelliSense displays me the members of STL-classes again  which it doesn t with Visual Studio 2017     So  my guess is that there might be also something wrong with Visual Studio itself  maybe something in the cache directory or in general something on your PC which is not directly related to a specific solution  which can be solved by a clean and complete re-installation of Visual Studio  I know  this is a stupid  solution   but in my case  only a fresh Visual Studio  2019  installation had an effect   As already mentioned  in my case  only STL classes were affected  IntelliSense wouldn t display their members which is odd  I thought  it could maybe have something to do with precompiled headers  Somewhere I read that the STL and the project should be on the same drive and putting them onto the same should solve the problem  But none of these routes led to success

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first close the solution  then solution cache file delete  in location  C  Users Documents Visual Studio Backup Files project cache file  then  suo file delete  then solution open and build     I hope solve your problem

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There are a lot of answers to delete the SUO   hidden solution files  In my case it was because I needed to run Visual Studio as an Admin in order publish   Which overrode those files with admin permissions   Now when running as a standard user I can not get rid of any errors  If I re-run in admin mode I am able to resolve all the errors

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tldr  Unload and reload the problem project  When this happens to me I  used to  try closing VS and reopen it  That probably worked about half of the time   When it didn t work I would close the solution  delete the  suo file  or the entire  vs folder  and re-open the solution  So far this has always worked for me  more than 10 times in the last 6 months   but it is slightly tedious because some things get reset such as your build mode  startup project  etc  Since it s usually just one project that s having the problem  I just tried unloading that project and reloading it  and this worked  My sample size is only 1 but it s much faster than the other two options so perhaps worth the attempt   Update  some of my co-workers have now tried this too  and so far it s worked every time   I suspect this works because it writes to the  suo file  and perhaps fixes the corrupted part of it that was causing the issue to begin with  Note  this appears to work for VS 2019  2017  and 2015

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Delete the hidden file path   your solution   vs  your solution Name  v15   suo

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I found that this can happen if the referenced project is targeting a higher version of the framework than the project that is trying to use it  You can tell if this is the problem by going to the output window and looking for something similar to this       The primary reference  my reference  could not be resolved because it   was built against the   NETFramework Version v4 7 2  framework  This   is a higher version than the currently targeted framework     NETFramework Version v4 7     The solution is to change the target framework of one or other of the projects

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Perhaps you try to reset your intellisense cache  I ve had a similar issue in visual studio 2012 when working in a large project with many partial class definitions  Reducing the partials solved the problem partially  clearing the intellisense cache also - for a while

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My symptoms in VS2019 were that I would build with some errors   Then I d fix the errors  and the build would work  as shown in the Output window  But the Errors windows still showed the old errors   I could run it just fine   Closing VS2019 and reopneing fixed the issue  but only for a little while   This started happening on version 16 4 3  This solution seems to work for me   Uncheck Tools- Option- Projects and Solutions- General- Allow parallel project initialization  I found this fix buried way down in the comments here  https   developercommunity visualstudio com content problem 483450 vs-2019-intellisense-reports-compile-errors-when-r html

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in my case vs was never retaining the imported namespaces in the project properties   references  when I tried to add check them again I couldn t and vs threw an error and when saved project vs crashed  When I reopened all the standard imported namespaces  system data etc     were all ticked again and it then was recognising everything without error

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REM DELETE ALL VS HIDDEN SOLUTION OPTION FILES DEL  A H  S   SUO

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I ve noticed that sometimes when switching git branches  Visual Studio  2017  will not recognize types from some files that had been added in the second branch  Deleting the  vs folder solves it  but it also trashes all your workspace settings  This trick seems to work well for me    Solution Explorer -  Find the file with the unrecognized class in it  Click Show All Files at the top of the Solution Explorer  Right-click the file -  Exclude from project  Right-click the file again -  Include in project    This causes Intellisense to parse the file that it missed when switching branches

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Following solution worked for me  1 - Close VS  2 - Delete  vs folder  3 - Open VS  4 - Build solution

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If you have ReSharper  try emptying the ReSharper cache      In menu  ReSharper   Options   Environment   General   Clear Caches   and disabling and re-enabling ReSharper      In menu  Tools   Options   ReSharper   General   Suspend   Restore

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So many things that could cause it  as evidenced by the long list of answers here   Here s what fixed it for me  having tried pretty much everything else first  Build your sulution in DEBUG mode   Then build it in RELEASE mode  it shouldn t build when it has red wavy lines  but in my case it was just warnings that should have had green wavy lines but it was getting in a muddle and giving them red wavy lines  and it built anyway even in release mode    Then build in in DEBUG mode   Spitting on your hands and turning around three times optional  Worked for me  when nothing else did

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I had a problem like this where Intellisense didn t seem to recognise the existence of one project  lots of  can t find this type    this namespace doesn t exist   etc  errors     Removing and re-adding the project reference in all the referencing projects would fix the issue  but the underlying cause could be fixed by editing the  proj file of the problem project   Near the top of the  missing  project   csproj file is an element    lt ProjectGuid gt  GUID  lt  ProjectGuid gt    and in all of the referencing projects  csproj files were project references    lt ProjectReference Include     OffendingProject OffendingProject csproj  gt     lt Project gt  ANOTHER-GUID  lt  Project gt     lt Name gt Offending Project lt  Name gt   lt  ProjectReference gt    The referencing GUID didn t match the project s GUID  Replacing  GUID  above with  ANOTHER-GUID  fixed the problem without having to go through every referencing project

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Occasionally I have to do a custom clean by going through all of the projects and manually deleting the  bin  and  obj  folders   To see them in Visual Studio  you ll have to enable hidden files and folders for each project  After this is done  rebuild the solution

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I cleaned solution  closed VS  reopened it  build solution  and red unresolved lines were cleaned and build succeeded

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A colleague of mine experienced this issue today  We tried many of the recommendations here and none worked except the solution described below   Problem   Project builds fine but Intellisense fails to recognize certain types and marks particular using statements as invalid   Solution   Change the  Solutions Platform   in VS 2017 this is the dropdown next to the Solution Configuration dropdown and has values such as x86  x64  AnyCPU  Mixed Platforms  etc   to AnyCPU    The platform for your project may vary  but it seems as though some references may not be valid for all platforms

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Clearing Resharper s cache did not help in my case  tried suspend restore  and also Repair Resharper  using latest download off JetBrains  website - neither of these helped  This is after I tried close reopen VS  restart my machine  repeat  Build Rebuild and combination thereof   It s interesting that suspending Resharper seemed to solve the problem after the 2nd restart of VS  but it was back after I enabled Resharper  lt -- I tried to do this sequence 2-3 times to ensure the pattern   Anyway  I was still having issues when I found this article    Quick tip  What to do when Visual Studio freaks out and everything is red   So I deleted the hidden  SUO file on the same folder level with solution  and it magically solved all reds   Note - for Visual Studio 2015  the  SUO file is in  vs  solution name  v14 hidden folder

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I solved this problem by deleting the temporary files of Microsoft  NET framework  Location   C  Windows Microsoft NET Framework64 v4 0 30319 Temporary ASP NET Files and C  Windows Microsoft NET Framework v4 0 30319 Temporary ASP NET Files

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Try hovering with the mouse over the underlined elements  It should normally tell you what the problem  To see a list of all the errors warnings  go to View    Error List  A table should open on the bottom of the IDE with all the errors warnings listed

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After trying all of the options listed I discovered yet another reason why this can happen  If somebody sent you the source code as a zip  or you downloaded a zip  Windows may have blocked all files  2 ways to solve this   Method 1   Right click on the original Zip file -  Check  Unblock  -  Click apply  Method 2   If that s not an option  rather than opening properties on every file in the solution folder simply open power shell and unblock recursively using the following   Get-ChildItem -Path  C   lt ROOT FOLDER OF SOLUTION gt    -Recurse   Unblock-File

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Ran into this issue with a single type not being recognized by Visual Studio which showed the red squiggle even though the solution built successfully  I noticed in the Solution Explorer the file did not have the expand arrow on the left which shows classes and properties on expansion   The fix was to Exclude the file from the project and save build which produced an expected error and then Include the file in the project and save and build   After performing these steps Visual Studio started to recognize my type again  Looking at the diff in git it appears the issue was due to line endings not matching on the  lt Compile Include         gt  line of my  csproj file

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Here s a collection of popular answers  Upvote the OP of the answer if it helped you  Option 1  Clean  Build and Refresh   Mike Fuchs option  As  Mike Fuchs mentioned  try the following operations   In menu  Build  gt  Clean Solution And In menu  Build  gt  Build Solution  and select the project in question  and click on the refresh button   Option 2  Clean  Close  Restart and Build   Pixel option  As  Pixel mentioned  try the following sequence of operations    Clean the solution Close Visual Studio Open Visual Studio Build solution   Option 3  Clear ReSharper cache   GammaOmega option  If you have ReSharper  try emptying the ReSharper cache   In menu  ReSharper  gt  Options  gt  Environment  gt  General  gt  Clear Caches  and disabling and re-enabling ReSharper   In menu  Tools  gt  Options  gt  ReSharper  gt  General  gt  Suspend   Restore  Option 4  Delete the  suo file   Neolisk option  As  Neolisk mentioned  deleting the  suo file might solve your problem  For Visual Studio 2015  the file is located in    Path of Solution   vs  Solution Name  v14  suo  And for Visual Studio 2017    Path of Solution   vs  Solution Name  v15  suo  Note that the  vs directory is hidden  Option 5  Unload and Reload Project   TTT option  As  TTT mentioned  try unloading the project that causes problems   In Solution Explorer  right-click on project  Unload Project   And re-loading it  In Solution Explorer  right-click on project  Reload Project   Option 6  Remove and add Microsoft CSharp reference   Guilherme option  As  Guilherme mentioned  try removing and adding the reference to  quot Microsoft CSharp quot  from the projects that have problems   In Solution Explorer  expand the project  expand  quot References quot   right-click on  quot Microsoft CSharp quot  and Remove  Then  right-click on References  gt  Add Reference  select  quot Microsoft CSharp quot  from the list and click OK

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0 - Right click on the Solution and clean solution  1 - Close VS   2 - Delete project s  suo file  3 - Open VS  4 - Build solution

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For my specific case it was a service reference another developer merged into the main branch  Which was perfectly fine except syntax highlight failed to resolve the generated service class and source was all red underlined  Cleaning  rebuilding  restarting did nothing    All I had to do was refresh the service reference and VS managed to put the pieces together behind the scenes  No changes in the source code or generated files

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Deleting  vs folder solved my problem    But it also reset my solution s current settings in VS  Like  my unloaded projects in the solution were re-loaded and all the pinned and opened documents were also closed when I restarted the VS

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for VS-2017  deleting  vs folder worked for me

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I ve just ran into this issue after reverting a git commit that added files back into my project   Cleaning and rebuilding the project didn t work  even if I closed VS inbetween each step   What eventually worked  was renaming the file to something else and changing it back again   facepalm

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Unload  amp  reload the project fixed this problem

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Had this issue at work  running VS2017    Tried all of the answers here   No joy   The project would build just fine  but was complaining that namespaces   types couldn t be found   Red squiggles all over the place   Lots of errors in the Error List window   My solution contained 3 projects   Discovered that 3 of the NuGet library references for one of the projects was out of line  Consolidated the referenced library versions  and Bingo   Hope this helps someone   Brett

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Sometimes if you just clean solution the errors are disappearing  but they may eventualy come back afer a while or at the next build

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I have tried all the 6 options  nothing worked for me  Below solution resolved my issue    Close VS  Delete the hidden   vs  folder next to your solution file  Restart VS and load the solution

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I found that happens frequently when using Git in Visual Studio 2017  switching branches where there is dependent code changes  Even though the project will build successfully  there will remain errors in the error list    These errors are often namespace issues and missing references  even when the library reference exists   To resolve    Close Visual Studio Delete the  sln-root  vs SlnName v15 suo file  hidden  Restart Visual Studio

[c#] Visual Studio displaying errors even if projects build

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