VS2010 Not Always Building Before Debugging

I have had a problem where VS2010 will 开发者_如何学运维not build my projects before debugging. Even when they have never been built before (i.e. on a fresh checkout from source control).

I will either find I am stepping through on the wrong lines of code (because the symbols are out of date), or an error message if there is no build output (bin\debug folder is empty).

Performing a build manually before debugging is the workaround.

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I'm answering this myself, so that Stack Overflow can be the canonical answer to this problem in case someone else experiences the same thing.

Essentially it's a VS configuration issue. Navigate to the options as follows:

Tools->Options->Projects and Solutions->Build and Run->On Run, when projects are out of date:

and make sure it is set to "Always Build" if it is not already.

Hope this helps someone, it's caused me a lot of trouble for weeks now.

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Go to the configuration manager, and change Debug->Mixed CPU to Debug->Any CPU, I had resolved mine with the same option.

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What resolved the problem for me was going to the configuration manager and making sure the "Build" checkbox was checked. In my case, it had somehow become un-checked:

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Update: I've found your answer and checked a Tools->Options->Projects and Solutions->Build and Run And a value of "On Run, when projects are out of date" is "Prompt to Build", but VS does not prompt! But then I found a problem in "Configuration Manager" - for some reason a mark "Build" disappear. It happened to my projects when I create a some project based on some another one using a copying a files and changing a project's and solution's GUIDs, names etc. inside a proj/sln files manually.