You will usually not get good C++ out of a binary unless you compiled in debugging information. Prepare to spend a lot of manual labor reversing the code.
What tool can decompile a DLL into C++ source code?
Best Reverse Engineering Tools for decompile a exe into C++ source code
DLL to C
DLL to C is a tool which can convert a DLL into compilable C/C++ code. When you lost the source code of a DLL, you can recover the source code with DLL to C. It can generate data structures for all data sections and disassemble the code section. It can also generate Function Relationship Tree, and then you can export the specified feature you want in the DLL easily. And it can convert assembly code to C code, and the C code is also compilable and reliable.
Supported OS: 64-bit & 32-bit of Windows 10/8/7/Vista/XP/ 2008(R2)/2003(R2)/2000/98
DLL to C，一个非常屌的工具，可以从dll decompiler上下载。DLL to C 是一个能够把所有DLL文件和部分EXE文件转换为可编译的C/C++代码的工具，转换之后生成的代码高度可靠，可直接编译运行，并且可以很容易地阅读和编辑。
https://www.dll-decompiler.com/
other tools:
Open MFC application to get source-code
ida and ida pro
Hex-Rays decompiler is probably the best in this field !!!
Use Hex-Rays Decompiler http://www.hex-rays.com/products/decompiler/index.shtml It converts executable programs into a human readable C-like pseudocode text
https://www.hex-rays.com/
Decompiler
Decompiler reads program binaries, decompiles them, infers data types, and emits structured C source code.
http://decompiler.sourceforge.net/
https://sourceforge.net/projects/decompiler/
dcc
DCC (Dex-to-C Compiler) is method-based aot compiler that can translate DEX code to C code.
The dcc Decompiler Example of Decompilation
Snowman
Snowman is a native code to C/C++ decompiler.
Examples:https://derevenets.com/examples.html
Reko decompiler