How to Detect if I'm Compiling Code with a particular Visual Studio version?

_MSC_VER and possibly _MSC_FULL_VER is what you need. You can also examine visualc.hpp in any recent boost install for some usage examples.

Some values for the more recent versions of the compiler are:

MSVC++ 14.24 _MSC_VER == 1924 (Visual Studio 2019 version 16.4)
MSVC++ 14.23 _MSC_VER == 1923 (Visual Studio 2019 version 16.3)
MSVC++ 14.22 _MSC_VER == 1922 (Visual Studio 2019 version 16.2)
MSVC++ 14.21 _MSC_VER == 1921 (Visual Studio 2019 version 16.1)
MSVC++ 14.2  _MSC_VER == 1920 (Visual Studio 2019 version 16.0)
MSVC++ 14.16 _MSC_VER == 1916 (Visual Studio 2017 version 15.9)
MSVC++ 14.15 _MSC_VER == 1915 (Visual Studio 2017 version 15.8)
MSVC++ 14.14 _MSC_VER == 1914 (Visual Studio 2017 version 15.7)
MSVC++ 14.13 _MSC_VER == 1913 (Visual Studio 2017 version 15.6)
MSVC++ 14.12 _MSC_VER == 1912 (Visual Studio 2017 version 15.5)
MSVC++ 14.11 _MSC_VER == 1911 (Visual Studio 2017 version 15.3)
MSVC++ 14.1  _MSC_VER == 1910 (Visual Studio 2017 version 15.0)
MSVC++ 14.0  _MSC_VER == 1900 (Visual Studio 2015 version 14.0)
MSVC++ 12.0  _MSC_VER == 1800 (Visual Studio 2013 version 12.0)
MSVC++ 11.0  _MSC_VER == 1700 (Visual Studio 2012 version 11.0)
MSVC++ 10.0  _MSC_VER == 1600 (Visual Studio 2010 version 10.0)
MSVC++ 9.0   _MSC_FULL_VER == 150030729 (Visual Studio 2008, SP1)
MSVC++ 9.0   _MSC_VER == 1500 (Visual Studio 2008 version 9.0)
MSVC++ 8.0   _MSC_VER == 1400 (Visual Studio 2005 version 8.0)
MSVC++ 7.1   _MSC_VER == 1310 (Visual Studio .NET 2003 version 7.1)
MSVC++ 7.0   _MSC_VER == 1300 (Visual Studio .NET 2002 version 7.0)
MSVC++ 6.0   _MSC_VER == 1200 (Visual Studio 6.0 version 6.0)
MSVC++ 5.0   _MSC_VER == 1100 (Visual Studio 97 version 5.0)

The version number above of course refers to the major version of your Visual studio you see in the about box, not to the year in the name. A thorough list can be found here. Starting recently, Visual Studio will start updating its ranges monotonically, meaning you should check ranges, rather than exact compiler values.

cl.exe /? will give a hint of the used version, e.g.:

c:\program files (x86)\microsoft visual studio 11.0\vc\bin>cl /?
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.50727.1 for x86
.....

_MSC_VER should be defined to a specific version number. You can either #ifdef on it, or you can use the actual define and do a runtime test. (If for some reason you wanted to run different code based on what compiler it was compiled with? Yeah, probably you were looking for the #ifdef. :))

By using the _MSC_VER macro.

This is a little old but should get you started:

//******************************************************************************
// Automated platform detection
//******************************************************************************

// _WIN32 is used by
// Visual C++
#ifdef _WIN32
#define __NT__
#endif

// Define __MAC__ platform indicator
#ifdef macintosh
#define __MAC__
#endif

// Define __OSX__ platform indicator
#ifdef __APPLE__
#define __OSX__
#endif

// Define __WIN16__ platform indicator 
#ifdef _Windows_
#ifndef __NT__
#define __WIN16__
#endif
#endif

// Define Windows CE platform indicator
#ifdef WIN32_PLATFORM_HPCPRO
#define __WINCE__
#endif

#if (_WIN32_WCE == 300) // for Pocket PC
#define __POCKETPC__
#define __WINCE__
//#if (_WIN32_WCE == 211) // for Palm-size PC 2.11 (Wyvern)
//#if (_WIN32_WCE == 201) // for Palm-size PC 2.01 (Gryphon)  
//#ifdef WIN32_PLATFORM_HPC2000 // for H/PC 2000 (Galileo)
#endif

In visual studio, go to help | about and look at the version of Visual Studio that you're using to compile your app.