GCC worth using on Windows to replace MSVC?

MSVC has the huge advantage of coming with an IDE that has no equals under Windows, including debugger support.

The probably best alternative for MinGW would be Code::Blocks, but there are worlds in between, especially regarding code completion and the debugger.

Also, MSVC lets you use some proprietary Microsoft stuff (MFC, ATL, and possibly others) that MinGW has no support for, and makes using GDI+ and DirectX easier and more straightforward (though it is possible to do both with MinGW).

Cygwin, as mentioned in another post, will have extra dependencies and possible license issues (the dependency is GPL, so your programs must be, too). MinGW does not have any such dependency or issue.

MinGW also compiles significantly slower than MSVC (though precompiled headers help a little).

Despite all that, GCC/MinGW is an entirely reliable quality compiler, which in my opinion outperforms any to date available version of MSVC in terms of quality of generated code.
This is somewhat less pronounced with the most recent versions of MSVC, but still visible. Especially for anything related to SSE, intrinsics, and inline assembly, GCC has been totally anihilating MSVC ever since (though they're slowly catching up).

Standards compliance is a lot better in GCC too, which can be a double-edged sword (because it can mean that some of your code won't compile on the more conforming compiler!), as is C++11 support.

MinGW optionally also supports DW2 exceptions, which are totally incompatible with the "normal" flavour and take more space in the executable, but on the positive side are "practically zero cost" in runtime.

I want to add some information because the field may have changed since the question was asked.

The main problem for switching away from MSVC was the lack of a good IDE that flawlessly integrates with MinGW . Visual Studio is a very powerful tool and was the only player on Windows for quite some time. However, Jetbrains released a preview version of their new C++ IDE CLion some days ago.

The main benefit comes when working on cross platform applications. In this case, a GCC based tool chain can make life much easier. Moreover, CLion narrowly integrates with CMake, which is also a big plus compared to Visual Studio. Therefore, in my opinion, it is worth to consider switching to MinGW now.

GCC's C++11 support is quite phenomenal (and quite up to par with standards conformance, now that <regex> has been implemented).

If you replace your compiler, you'll need to make sure every dependency can be built with that new compiler. They're not made to be substitutable plugins (although Clang is working on becoming that way).

GCC is a fine compiler, and can produce code that has pretty much the same performance, if not better, than MSVC. It is missing some low-level Windows-specific features though.

Apart from this, to answer your questions:

1. To get VS to use GCC as a compiler, you'd pretty much need to turn to makefiles or custom build steps all the way. You'd be much better off compiling from the commandline and using CMake or something similar.
2. You cannot use the VS debugger for GCC code. GCC outputs GDB compatible debug information, and the VS debug format is proprietary, so nothing will change in that area anytime soon.
3. Code quality is just as good as you'd want it. See above.
4. No, the quality of your code will actually increase, as GCC will point out several assumed standard extensions MSVC would hide from you. All self-respecting open source projects can be compiled with GCC.

I my humble opinion, it's depends how someone started to code in the first place. I've been using g++ and gcc for more than 20 years now but the reason why i keep using gcc is mainly for licensing reasons. Although i like it too when i don't have a bunch of runtime dependencies or dll's to bundle with my stuff since i came from the DOS era, i still like my stuff small and fast. gcc for windows comes with standard win32 libraries and common control but i had to develop my own win32 controls for stuff that might require mcf shit to work properly or just to look nicer.

Although gcc might have strong support over internet, when it comes to win32 stuff, many rely on mcf and vc proprietary stuff so again, one may have to work his own issues around and be creative when difficulty arises.

I think it's all about needs and circumstances. If you are just a hobbyist coders and have the time for researches, creating you own libs and stuff but you want a solid compiler that's around since the late 80's and free, gcc sound perfect for the job.

But in the industry visual studio is a must if you want to be competitive and stay in the race. Many hardware manufacturers would prefer bundling visual studio compatible libraries for they hardware over some opensource gnu stuff.

That's my two cents.

It can't be used as a direct swap-out replacement for the microsoft compilers, for a start it has a vastly different set of command line arguments and compiler specific options.

You can make use of MinGW or Cygwin to write software but introduce extra dependencies ( especially in the case of cygwin ).

One not often touted advantage of gcc over cl is that gcc can be used with ccache to drastically speed up rebuilds or distcc to build using several other machines as compiler slaves.