What is the difference between Debug and Release in Visual Studio?

“Debug” and “Release” are actually just two labels for a whole slew of settings that can affect your build and debugging.

In “Debug” mode you usually have the following:

• Program Debug Database files, which allow you to follow the execution of the program quite closely in the source during run-time.
• All optimizations turned off, which allows you to inspect the value of variables and trace into functions that might otherwise have been optimized away or in-lined
• A _DEBUG preprocessor definition that allows you to write code that acts differently in debug mode compared to release, for example to instrument ASSERTs that should only be used while debugging
• Linking to libraries that have also been compiled with debugging options on, which are usually not deployed to actual customers (for reasons of size and security)
  
  

In “Release” mode optimizations are turned on (though there are multiple options available) and the _DEBUG preprocessor definition is not defined. Usually you will still want to generate the PDB files though, because it’s highly useful to be able to “debug” in release mode when things are running faster.


Here’s the difference between VCXPROJ context

RELEASE

<PropertyGroup>
    <WholeProgramOptimization>true</WholeProgramOptimization>

<ClCompile>
    <Optimization>MaxSpeed</Optimization>
    <FunctionLevelLinking>true</FunctionLevelLinking>
    <IntrinsicFunctions>true</IntrinsicFunctions>
<Link>
    <EnableCOMDATFolding>true</EnableCOMDATFolding>
    <OptimizeReferences>true</OptimizeReferences>

DEBUG

<PropertyGroup>
    <UseDebugLibraries>true</UseDebugLibraries>`

<ClCompile>
    <Optimization>Disabled</Optimization>