Functions like malloc , free , and realloc for dynamic memory allocation.
: When you statically link the CRT, your linker takes the actual code for the CRT functions from libcmt.lib and embeds it directly into your final .exe or .dll file. This creates a larger executable, but it becomes self-contained. The major advantage is that your application does not require any external CRT DLLs to be present on the target system to run. However, a significant downside emerges when multiple components in a process statically link the CRT. Because each component has its own copy of the CRT code, they also have separate internal states. For example, if one DLL uses the strtok function to parse a string, its internal parsing state is completely separate from the state used by the main .exe file. This can lead to unpredictable behavior. Furthermore, mixing different versions of statically linked CRTs in the same process can cause hard-to-diagnose errors and memory corruption.
When building your project, you must choose how to link the CRT:
: This occurs when mixing static ( /MT ) and dynamic ( /MD ) libraries within the same project. If a third-party dependency uses static linking while the main project uses dynamic linking, their respective CRT routines conflict during the compilation phase. microsoft c runtime
The application links dynamically against the CRT DLLs ( vcruntime140.dll and ucrtbase.dll ).
The remaining functions—those deeply tied to the compiler itself, such as exception handling, runtime type information (RTTI), and process startup—were moved into a separate, versioned library called vcruntime140.dll . Visual Studio 2015, 2017, 2019, 2022, and subsequent releases share this same binary compatibility layer, allowing tools compiled across different recent VS versions to interoperate seamlessly. Linking Options: Static vs. Dynamic
This component contains the core C standard library functions adhering to the ISO C99 standard. It was transformed into a Windows operating system component, now shipping as part of Windows 10 and later versions. For older versions of Windows, it can be installed via Windows Update. The UCRT implements a stable Application Binary Interface (ABI), meaning it is no longer tied to a specific Visual Studio version. Functions like malloc , free , and realloc
Historically, every major release of Visual C++ shipped with its own distinct, self-contained runtime library (e.g., msvcr100.dll for Visual Studio 2010, msvcr120.dll for Visual Studio 2013). This created massive deployment friction, as users had to install dozens of "Visual C++ Redistributables" to run different applications.
This architectural change has profound implications:
The Architecture and Evolution of the Microsoft C Runtime (CRT) The major advantage is that your application does
+-----------------------------------------------------------------------+ | Your Application | +-----------------------------------------------------------------------+ | +-----------------------+-----------------------+ | | v v +-----------------------+ +-----------------------+ | VC++ Runtime (VCRuntime) | | Universal CRT (UCRT) | | e.g., vcruntime140.dll | | ucrtbase.dll | +-----------------------+ +-----------------------+ | C++ features, name | | ISO C99 standard lib, | | mangling, SEH support | | POSIX, file I/O | +-----------------------+ +-----------------------+ | | +-----------------------+-----------------------+ | v +-----------------------------------------------------------------------+ | Windows Operating System | +-----------------------------------------------------------------------+ 1. The Universal CRT ( ucrtbase.dll )
Even with a solid understanding of the CRT, problems can still arise. Here are some of the most common issues developers and users face: