How do I build against the UCRT with mingw-w64?

Question

I would like to be able to use mingw-w64 to build binaries that link to the Universal CRT available with Visual Studio 2015+ instead of MSVCRT.lib. The release notes for mingw-w64 v6.0.0 include the following: "Massive additions to support UCRT thanks to Martin Storsjö"

Unfortunately my searches have not revealed the documentation on how to use this support.

Does anyone know what options I need to supply and where to supply them?

Answer 1

Well, I have done it along with VS 2017. But as far as I understand both VS 2015 and VS 2017 use the VCRUNTIME140.DLL, so no worries here.

It is divided into two steps:

1. Creating an import library for VCRUNTIME140.DLL:

This is done by doing the following:

mkdir scratch; cd scratch
cp C:/Windows/System32/vcruntime140.dll .
dumpbin /exports vcruntime140.dll > exports.txt
echo LIBRARY VCRUNTIME140 > vcruntime140.def
echo EXPORTS >> vcruntime140.def
tail +20 exports.txt | head -n -10 | awk '{print $4}' >> vcruntime140.def
lib /def:vcruntime140.def /out:libvcruntime140.a /machine:x86
cp libvcruntime140.a $(MINGW_ROOT)/i686-w64-mingw32/lib

2. Change the way MinGW GCC operates to link against VCRUNTIME140 and UCRT instead of MSVCRT

gcc -dumpspecs > $(MINGW_ROOT)/lib/gcc/i686-w64-mingw32/$(GCC_VERSION)/specs

1. Add -D_UCRT to cpp and cc1plus sections of the specs file. This will prevent undefined references linking errors for the scanf functions family. Check my other question.
2. Replace -lmsvcrt to -lvcruntime140 -lucrt in the libgcc section of the specs file.

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Please exchange $(MINGW_ROOT) with the location of where u have MinGW.

Notes:

• The platform signature part, i686-w64-mingw32, within the paths I included may differ for your case. I believe based on the architecture. So you may have to modify that accordingly.
• You need to use a relatively new MinGW that has libucrt.a in the $(MINGW_ROOT)/i686-w64-mingw32/lib folder. I am using MinGW 7.0.0 with GCC 7.4.0.