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Debugging C# application - Visual Studio

I am trying to learn C# and have followed the instructions in this tutorial
I have created a project, added the controls to the design surface and added code to the button click event. When I get to the part which asks me to test the application, I click "start debugging" and I get an error message saying
There were build errors, would you like to continue and run the last successful build?
If I click no, nothing happens. If I click yes I get another error saying:
Visual Studio cannot start debugging because the debug target 'C:\Users\hp\source\repos\HelloWPFApp\HelloWPFApp\bin\Debug\HelloWPFApp.exe' is missing.
As a complete beginner I have no idea why this exe file is missing or how to fix it. Could someone point me in the right direction at all?

It's possible that your code has never compiled. Press Ctrl-Shift-B and try again (or look in the Build menu).

First: You should clean the project than Build project again.
Second: Run project by pressing F5
Executable file you can find in bin/Debug folder in your root of project.

I do not have VS now, why don't you rebuild (or rebuild-all) your project, and if successfully rebuilds check whether the executable file exists in that folder, and also check the release folder, if it is there then change rebuild option to debug, as far as i remember you will see a drop down, on the toolbar,

Visual Studio doesn't show me the red squiggle Intellisense errors [duplicate]

My Visual Studio (2008) Editor has stopped to underline Errors (this nifty wavy red lines). I can't really tell when, but it can be related to the installation of .Net Framework 3.5 SP 1 or the MVC Beta (which I guess is unlikely). Furthermore have I installed and uninstalled both CodeRush and Resharper for evaluation purposes (decided not to keep either one of them).
Does anyone know the problem and how to restore this functionality again?

Have you checked Tools→Options...→Text Editor→C#→Advanced→Underline errors in the editor?
I usually like to reset my settings after messing around with plugins, as they tend to mess with settings: Tools→Import and Export Settings...→Reset all settings.

About possible causes.
For VS 2012 and 2013 if you have more than one instance of Visual Studio on different machines binded to one "live" account and have installed ReSharper on one of them, it disables the native IntelliSense and error underlines (to replace by it's own rules) that will be synchronised through your account to another machine without ReSharper.

Found it in Visual Studio 2019 as: Tools > Options > Text Editor > General > Show error squiggles

This is generally called Disable Squiggly or Wavy lines in Visual Studio.
How you will do in Visual studio 2013?
TOOLS -> Options... -> Text Editor -> C/C++ -> Advanced -> Disable Squiggles: True/False (Under IntelliSense) -> Press OK

I know its an old question, and with various solutions, but I have fixed it in different way. I'm working with Unity3D on my C# code using VS2017, when suddenly VS decides to stop underlining error while im typing. However, if I close the file tab and reopen, it suddenly undelines the error.
For example:
class A {
public int x;
s;
}
should obvsiouly give an error for that lonely 's' symbol. But, VS doesn't underline it until I close and reopen this file tab.
Solution:
Copied the entire Unity Project folder (which is like a regular VS Solution folder basically) and worked with the new folder, which issue was gone there.

For visual studio 2017 act according to HeeJae's comments in:
https://developercommunity.visualstudio.com/content/problem/113112/design-time-error-checking-isnt-working.html
i.e:
Hi. you are probably hitting a known issue. can you try this?
1.Update to latest release If that doesn’t solve it
2.Go to Tools\Options\Projects and Solutions\General and uncheck “Allow parallel project initialization”.
3.Close VS.
4.Delete the “.vs” directory beside their solution file.
5.Reopen VS.
..
thank you
You can re-enable the "Allow parallel project initialization" option after the issue was solved.
I tried to upgrade VS, reset VS settings, clear VS cache and everything people do conventionally but none of them solved this issue! At the end the mentioned solution worked for me magically.
Good luck

Unloading and loading same project again from the solution does the trick. Just right click on the project and click "Unload Project". Once unloaded, again right click the same project and click "Reload Project". Error highlighting will return.

I had the same issue with 2017. There was a 'disable intelisense' option, make sure that is set to false.

For everyone wondering in 2021..
search for "C_Cpp.errorSquiggles" in the settings.
Make sure to have it active for the user, as well as the workspace.
No need to restart Visual Studio.

For me (VS 2019) , after trying the other answers also, setting the scope of analysis from "Current document" to Open document" brought back the missing error markers

Just go to settings and search for errors and Image in Error Squiggles. You can see the Error squiggles (Modified: Workspace - Right now you can't see it because I modified it). Just click on modified and you will see the disabled option. If by mistake you disabled it, just enable it and you can see the red line errors again in your code.

In latest edition, check for .vscode folder in same project folder. There will be a setting.json file in that. Delete the key value pair of "C_Cpp.errorSquiggles": "Disabled". Restart the vs code.

Visual Studio 2012 won't let me debug

I can't seem to be able to debug. When I try to, I don't get any build errors, and the layout changes to debug mode, but the windows never pops up. I have an orange bar at the bottom of VS, which I think is standard, but nothing happens after that. It's not just in the project I'm working on. I have started a new WFA and tried to debug without adding any code and the same thing happens. Anybody have similar issues?

I've encountered this before. Not sure what causes it, but generally it is one of a couple of things to fix it.
make sure you are building in debug and not release
close VS, go to the project's dir and delete the obj and bin directories. Reopen in VS and rebuild.
there is an option under tools - options - build (iirc) that allows for checking if source is same as code file. However, you should see a message in output window if this is the case.
on the project properties in the build (iirc) you can throttle the pdb file from full debug symbols to no pdb at all. If you are not the only person on the project check this setting still has full pdb enabled (low probability this got changed though)
make sure you're on the right platform that you are building to (x64 vs x32)
...lots more, but a starting place...
Addendum as per comment...
So, those messages are good. It is saying there are no problems (but it sounds like you already know that :) ). I would start with the general debug options you mention. Do this on a hello world app. That way you can troubleshoot the lowest common first. Here are my settings. Try to match them and see if that works. For example, I know "ask before deleting breakpoint" is irrelevant, but "break all processes when one process breaks" is important. So, I just added them all to make it easier to troubleshoot.
ALso, make sure you are getting a red dot here like so in your code in visual studio (I've seen instances where VS won't let you put this here):

Right click on the project
Click on the properties.
go to web.
Check the Box for Enable Edit and Continue .
Hope that helps :)

This is an issue with visual studio 2012. It doesn't ALWAYS show up. I've found that if you stop your program during debugging, or if you close the console window, this will almost always trigger.
However, letting it run to completion isn't enough either, sometimes this just happens.
Also you can build your application in debug mode, go to the output, run the program, and attach to that process. :P

Amazing answers already given but they dont help in the purpose. So here is my finding, no matter if i am late in answering, but it really works for me.
Even if you are developing a web app, just go to the website properties by right-clicking the project and then you see a "Web" tab on left as i have highlighted. Then just check the box saying "Enable Edit and Continue". Thats all you need to do. it works for me!

I had a similar problem, and solution was absolutely dumb. VS was confused with two instances of Internet Explorer in “Browse with” setting. So, I set Google Chrome (any browser) as default, and then set IE as default again. It deleted the other instance of IE (only one remained) and debugging was enabled.
Hope it help!

I had a similar issue.
I added up:
using namespace std;
and this solved the problem

For me, uninstalling the Redgate's Reflector plugin that had expired fixed it. I spent more than 4 hours uninstalling, rebooting, reverting to older code, etc etc..

When my default browser was changed to CHROME, I could no longer debug my User Interface. Setting IE back to the default browser fixed it. Alternatively you can attach the process plug-in during debug.

I had the same problem with my desktop application and as this forum says you should mark your project as a startup project, since visual studio has unmarked. It worked just fine for me an I believe it will help other people that may have this problem, since I believe you have finished this project.

One of my VB .NET Winforms projects wouldn't allow debugging.
This was due to the configuration manager set to 'Release' even though the toolbar dropdown indicated 'Debug'.
You need to select the mode dropdown and select the last option 'Configuration Manager' and ensure that the main project is set to 'Debug' and not 'Release'

Install Microsoft SSDTSetup.exe 450Kb and Close the SSDT tool during install. After installation open the SSDT tool and execute the script task and Component with breakpoint. Worked for me

try checking your output without debugging
Ctrl + F5
good luck

Visual Studio 2012 not compiling anymore after changes made

i recently installed VS 12 Service Pack 1.
Since then, i noticed Visual Studio doesn't compile my project on start if changes were made.
Normally if you start (debugging) a project which has some changes, it recompiles it and starts then. But now, i always get debugging errors like "this breakpoint can´t be reached, because the source code is unequal to the runtime code" or whatever.
It´s annoying to recompile it manually always before starting - I always forget that :-/
Is there any option to fix this?

Can you check if the build on run option is set?
You will find it under Tools->Options->Project and Solutions->Build and Run.
I dont have a good answer as to why this would have been flipped just via installing the update1.

I think that you should enter the Solution's Property Pages (by right clicking the solution in the Solution Explorer pane) and setting the 'build' check-box of the relevant project.

How do I remedy "The breakpoint will not currently be hit. No symbols have been loaded for this document." warning?

A C# desktop application (on the Visual Studio Express edition) worked, but then it didn't work 5 seconds later.
I tried the following:
Ensure debug configuration, debug flag, and full debug information are set on all assemblies.
Delete all bin and obj folders and all DLL files related to the project from my entire machine.
Recreate projects causing the problem from scratch.
Reboot.
I have two Windows Forms projects in the solution. One of them loads the debug information, one doesn't. They both refer to the assembly I'm trying to get debug information on in exactly the same way in the project file. Any ideas?
I want to add here, mostly for myself when I come back to review this question, that symbols are not loaded until the assembly is loaded, and the assembly is not loaded until it is needed. If the breakpoint is in a library that is only used in one function in your main assembly, the symbols will not be loaded (and it will show the breakpoint as not being hit) until that function is called.

Start debugging, as soon as you've arrived at a breakpoint or used Debug > Break All, use Debug > Windows > Modules. You'll see a list of all the assemblies that are loaded into the process. Locate the one you want to get debug info for. Right-click it and select Symbol Load Information. You'll get a dialog that lists all the directories where it looked for the .pdb file for the assembly. Verify that list against the actual .pdb location. Make sure it doesn't find an old one.
In normal projects, the assembly and its .pdb file should always have been copied by the IDE into the same folder as your .exe, i.e. the bin\Debug folder of your project. Make sure you remove one from the GAC if you've been playing with it.

Check to make sure that you are not in release but in Debug.
When in debug:
First try rebuilding your project by right mouse click the project > Rebuild
If that doesn't work, try a clean of the project (right mouse click on the project > clean)
If that didn't work check this:
Right mouse click your project
Select [Properties]
Select the [Build] tab
Make sure [Define DEBUG constant] and [Define TRACE constant] are checked
Make sure [Optimize Code] is unchecked
Click the [Advanced] button at the bottom of the Build tabpage
Make sure that [Debug Info:] is set to [full]
Click [OK] and rebuild the project ;-)
(step 7 generates the .pdb files, these are the debugging symbols)

Uncheck the "Enable Just My Code" option in the
Tools/Options/Debugging/General

Just something simple to try - you may have tried it already.
Right click the Solution in solution explorer, click "clean solution", this deletes all the compiled and temporary files associated with a solution.
Do a rebuild of the solution and try to debug again.
I've also had troubles with breakpoints multiple projects in a solution - some compiled as x86, some as x64.

The selected answer led me to fix my problem. But I need to do a few things more:
Even with "Debug" selected in the dropdown:
And in the project Properties > Build:
The Visual Studio was not loading symbols to a specific project. So in that dropdown I select "Configuration Manager" and saw that the settings to my web project was incorrect:
Then I set that to "Debug" and it started to generate the .pdb file.
BUT I need to manually copy the PDB and DLL and put in the folder that VS was looking (here is where the selected answer helped me):

Sometimes, even though it gives you this error, the Breakpoint still gets hit, so just ignore the error.
This happens fairly often in the Views of an MVC web app, i.e. .cshtml.

I was able to fix the error by simply setting the option in the 'Attach to Process' to 'Automatically determine the type of code to debug' option as shown in the attached screenshot.
Simply follow the steps below:
Go to Debug from the menu bar
Click on Attach to Process
Near the Attach to option, click on the Select button
The Select Code Type window will appear
Now select the option Automatically determine the type of code to debug and click the OK button.

Debug > Windows > Modules to see what modules were being loaded put me in the right direction.
In my case IIS Express seemed to be loading a different DLL from the temporary ASP.NET files.
The solution?
Browse to C:\Users\<YOUR USER>\AppData\Local\Temp\Temporary ASP.NET Files\vs
Delete everything in this directory!

Check if your .pbd file is missing in your bin/Debug folder. If it is then go to "Properties" of your project, selected "Build" and then "Advanced" at the bottom. Choose "full" under "Debug info" in the new window that appeared. This was my issue and solved it for me.

In my case "Optimize Code" was checked in my project properties. This caused VS to see my assembly as "not my code", and in turn, it did not load symbols for it.
The solution was to uncheck this.

Try running visual studio as an administrator within windows.

You need to enable "Generate debug info" in compiler settings

I tried everything mentioned above, but nothing worked.
[Clean solution, and check for PDB files etc.]
Even publishing the same solution did not resolve the issue.
Then I went to back to what I usually do to resolve (fool this stubborn Visual Studio)
All I did was to make a deliberate change in code and publish the solution.
Then I reverted the change and published again.
Voila [PDB files rid of evil spirits].. Not a smart resolution, but this did work.. :-|

We found the cause of our problem. This code was using the "CodeBehind" attribute in the Page directive of the .aspx file instead of the "CodeFile" attribute (ASP.NET 2.0 and beyond). After days of desperation, a simple search and replace solved the problem.

Option "Start debugging, Debug + Windows + Modules" does not exist in Microsoft Visual Studio Express 2013 edition.
Unchecking "Use Managed Compatibility Mode" in Tools Options Debugging fixes this.

Webapplications (IIS Express) only:
Rightclick IIS Express Tray and close the IIS.
Clean Solution

Clean solution and Rebuild
Check the configuration is set to Debug
Make sure that the PDB file is in the Debug folder it self
From Debug menu click Enable All Break points

Make sure you're in Debug and not is release by choosing debug in the dropdown menu like you can see in the picture below.
Then, try cleaning your project by clicking the right button in your mouse on the solution in the solution explorer window and choosing Clean solution.
Then rebuild your solution by clicking the right button in your mouse on the solution in the solution explorer window and choose Rebuild solution

Check are the following two setting the same in Visual Studio:
Right click test project, go to Properties, Build tab, and look at Platform target
Mine are all set to "Any CPU" so x64
On the Main Menu bar, go to Test, Test Settings, Default Processor Architecture
Mine was set to X86
Changing this to X64 to match above setting made the built in Visual Studio menu “Debug Test(s)” work and hit breakpoints that were previously ignored with the message “The breakpoint will not currently be hit. No symbols have been loaded for this document”.
Update:
For Visual Studio 2019 the menus have been moved around a bit:

I also had the same issue what I rebuild the whole solution (including refereced projects) in x86( or x64)
Even though I set all of my projects to x86 from Configuration Manager (Build->ConfigManager) some of my projects were not set to x86.
So Just to make sure right click on the project and follow
project -> properties -> Debug Tab, verify Configuration and Platform.

The .dll where I want to stop debugger and the associated .pdb files where copied near the .exe file. Those files had an older date so I thought they weren't updated in the runtime. I manually deleted them, Visual Studio create another pair AND put this new pair near the .exe. Now the breakpoint works!
Maybe Visual Studio cannot copy and REPLACE existing files (.dll and .pdb) near the .exe since there are another there. So if I deleted manually then VS could create new one near .exe.
I think that the root cause of the problem is that the Visual Studio use another file in runtime, no the file from the project, with the stop.

Instead of doing all these things just Close and reopen

Project Properties (then select your build config) > Build Tab > Advanced... > Debug Info (dropdown)
Set to 'all' or 'pdb-only' then rebuild

This took me a while tried other options above and for some strange reason debugging stopped working.
Tool -> Options -> Debugging -> General -> (untick) "Require source files to exactly match the original version" option

I was integrating a C# application with a static library using VS10 - which I'm new to. I wrote a managed code dll to interface them. I could set breakpoints everywhere but the static lib. I got the message described above - no symbols have been loaded for this document. I tried many of the suggestions above. I could see that the symbols weren't being loaded. I finally noticed a check box Configuration Debug, Enable unmanaged code debugging. That allowed me to set breakpoints in the static lib functions.

In my case, I was compiling a class library (DLL). No modules seem to be loaded in Debug -> Modules, so I couldn't even load the symbols manually.
My solution was to add this line to my code:
System.Diagnostics.Debugger.Launch();
Once this code is reached, an exception is triggered and .NET Framework shows a dialog box asking which Visual Studio (i.e. new instance of VS 2008, new instance of VS 2013, etc) you want to use to debug the program. You can choose the existing instance of VS with your project loaded. This will attach the process to your VS session and load all symbols, and now you can debug your project.
Of course, the compilation has to be done using the Debug configuration, not Release.

For an ASP.Net application, check the properties of the site, ASP.NET tab. Ensure that the correct ASP.NET version is selected.

I think the source if this error is, the debug symbols have a hard time surfacing to the solution after building for release.
I tried all the other answers -- generally, regenerating .pdb symbols or checking their location, cleaning and rebuilding project, ensuring active configuration is not Release etc.
What eventually worked for me is right-clicking on the project in solution explorer > Debug > Start new instance.

After trying a bunch of these, the thing that ultimately worked for me was this:
In Debug > Options > General, uncheck Enable Edit and Continue.

this happened to me after copy paste another webservice asmx file into an existing webservice, resulting in the same error when trying to debug the recently added service, to be able to debug I had to start without debug, then attach to the process. its weird but its the only way i found to be able to debug.