Introduction
Whenever you do a build from Visual Studio, normally, you also get a PDB file besides your executable file. You can see this file in the ..bin\Debug or ..bin\Release directory.
This PDB file keeps a mapping to your source code lines and executable code in your assembly. Also, the original locations of the source code files from which a build was done is stored inside a PDB file.
This means that if you build a class library which had a single file located at G:\ClassLibrary\Class1.cs, this path will be stored inside ClassLibrary.pdb.
What is important to remember from all this is that without a PDB file it is impossible to do source code step-in debugging.
Real-life scenario
So, suppose I do a build on my drive G:\ClassLibrary1, for a class library.
I give you a ClassLibrary.dll and a ClassLibrary.pdb file, or you get them by checking them out from source control.
You reference the ClassLibrary.dll in your project and you use a class from the library.
If you now try to step into class code from the library the following will happen:
Visual Studio tries to locate a ClassLibrary.pdb file in a couple of locations
1.1 If it doesn't find it, you get a "Browse to find source" disabled
page. Remember, you can't debug without a valid PDB file.
1.2 If it does find a PDB file, it looks inside the PDB file and sees that you are trying to debug Class1.cs which was originally built from
G:\ClassLibrary1\Class1.cs
and looks on your computer for that file.
1.2.1 If it finds it, it steps into the code automatically.
1.2.2 If it doesn't find it, you get the following dialog:
![Browse to source file]()
If you press Cancel, you will be presented with the: "No source available" and you will have "Browse to find source" enabled in this case.
![Enter image description here]()
Why? Because you have a valid PDB file, but Visual Studio can't possibly know where you have the source code for ClassLibrary1 on your computer or if you even have it on your computer. That's why you got the dialog -> so that you can point Visual Studio to the exact location of the source code file.
Final notes
So what will you do when you get a browse to find source disabled?
In Visual Studio, you open menu Debug -> Windows -> Call stack.
You right click on the top call stak instruction and you choose "Symbol Load Information". It will show you the locations where Visual Studio has tried to find a valid PDB file.
- 1.a If you only see "Cannot find or open PDB file" messages put a valid PDB file at any of these locations. (You might have to scroll right to see the messages) Stop and start debugging again.
- 1.b If you see a "PDB does not match the image" message it means the following. Visual Studio has found a PDB file, but it is for another build. If I build ClassLibrary1.dll and give it to you, and then I build it again without changing a single line of code and then give you the PDB, and you try
to debug
classLibrary1.dll you will get this message. The assembly and its PDB file must be exactly from the same build, otherwise you will get this message. (This check is done using some unique number put inside the assembly and PDB file every time you do a built)
- 1.c You see a "symbols loaded" message but still get a "Browse to find" disabled. It means that the PDB file you have is not good for step-in debugging. Some PDB files you try to use don't have all the information in them necessary for step-in debugging. I think you can control this from somewhere in the advanced build settings, but I haven't tried it though, because I want to have usable PDB files generated everytime I do a build. This situation often happens if you try to debug the source code of the .NET framework itself and Microsoft hasn't put usable PDB files for the source code, but instead Microsoft has put some PDB files which can't be used for step-in debug. This happens more often than you think, because often Microsoft makes updates (patches) to the .NET Framework source code. These updates silently install onto your computer via Windows Update, and you are surprised to see that yesterday you could debug .NET Framework source code and today you can't. It usually takes some time until they put a valid PDB file for the latest code. In this case you can use .NET Reflector Pro step-debug ability or a virtual machine which has a .NET framework version with usable PDB files and disable Windows Update on that machine.
