The Microsoft C Runtime (CRT) is the foundational layer that allows C and C++ programs to function on the Windows operating system. Far from being just a background component, it provides the essential "glue" between a developer’s code and the Windows kernel. The Core Role of the CRT
Modern Microsoft C development involves three primary library layers that work together: Functionality Deployment Universal CRT (UCRT) Standard ISO C99 library functions (e.g., OS Component (Windows 10+)
Even if you write “modern C++” (using std::vector, std::string, std::unique_ptr), the CRT is still there underneath:
When C became the lingua franca for systems and application programming, compiler vendors wrapped common functionality into runtime libraries. These runtimes provided consistent implementations of the C standard library—functions like printf, malloc, fopen, and strcmp—and handled startup and shutdown chores for C and C++ programs. Microsoft’s runtime evolved from this tradition, first as part of its C compiler toolchains for MS-DOS and then as a core part of Microsoft Visual C++ for Windows.