MS Visual C++ runtime library - what for?

Question

What's in MS Visual C++ runtime library? I mean, I googled it, and I always found things like help, app xxxx gives me MS Visual C++ runtime library error, with no explanation.

I thought that Windows C runtime libraries come with Windows? Not with VC++? Thanks.

EDIT: First, thanks for answers. I thing now I have bad idea of runtime libraries in windows. I mean, the first part, that Windows internally has its win32 API and so, that's OK, I knew it. Also, that Win32API are from kernel and user parts.

But I always thought that functions like GDI are accessed as DLL (which I still believe they are). But I thought even functions like printf and so are in some windows file.

So, am I right, when I know get it that "simple" functions like printf need to be linked directly and than use only Kernel part of OS directly, and more sophisticated Windows API functions are linked as dlls, therefore ARE NOT distributed with compiler but with OS? And they subsequently access Kernel?

I mean, lets say GDI, I tell it to draw picture, it makes all the hard work in user mode and than call kernel function which puts it all in framebuffer?

And last thought, why is this even solved this way? I mean, if VC++ runtime is just layer between C and WinAPI, why cant VC++ call directly WinAPI?

Answer 1

A brief answer would be that the MSVS C/C++ runtime implements functions like malloc/free, stdio, iostream and some c++-stuff like dynamic_cast and exception handling. These differs between versions of visual studio, so there are different runtimes for different versions.

Windows ship mostly with a C API (the Win32 API) which rather different from the C/C++ standard library. The MSVS C/C++ runtime calls into this API to allocate memory, etc etc.

(I suppose some of the applications included with Windows are written with MSVS and in C++, so they do include the MSVS runtime for that version.)

Also, the runtime changes as new Visual Studio versions are released. A Windows release lasts much longer than that.

Answer 2

This is an oversimplification, but it will give you the gist. The MSVCRT is a set of DLLs that implements parts of the C++ language. Functions like printf, memcpy and the like are implemented in these DLLs.

Every program that is compiled with a particular compiler and dynamically linked to the C++ runtimes must somehow have the correct version of the CRT binaries on the target machine. As a result, applications that ship to end users are often (usually?) also shipped with a package of these DLLs. This package is called a "redistributable" (or "redist"), and there is a different one for every combination of exact compiler version and target platform. For example, there are seperate and distinct redists for each of the following:

• MSVC 10, 64-bit windows
• MSVC 10, 32-bit windows
• MSVC9, 64-bit windows
• MSVC9 SP1, 64-bit windows

et cetera.

Yes, Windows usually "comes with" some version of the CRT. However, it comes with the version(s) that it needs in order to run the apps that shipped with Windows. If Windows and all it's apps were compiled in MSVC8 SP2 and your app is compiled in MSVC10, the CRT you require won't be present on the box simply because it's running Windows.

This is why its common practice to ship apps along with redists.

EDIT:

By way of Houdini like magic, I predict your next question will be "where do I get the redists?"

The answer is, from MicroSoft. Try a google search for "msvc 9 x64 redist" and you will find:

http://www.microsoft.com/downloads/en/details.aspx?familyid=bd2a6171-e2d6-4230-b809-9a8d7548c1b6&displaylang=en

Answer 3

They are the libraries that implement the C and C++ standard library functions. Standard functions such as printf are implemented in these libraries.

The core Windows libraries only provide interfaces to system calls, i.e. the Win32 API, since that is all you need to build a full-featured Windows application. The VC++ libraries are mostly wrappers around this API, and are analogous to the glibc library on Linux.

As an example, malloc from the C library might in turn use the VirtualAlloc API to allocate memory.

Answer 4

Programs compiled with Visual C++ require a "runtime" - this is a bit of code that handles application startup/shutdown, memory allocation/deallocation, support for reading and writing files, etc.

This is not part of the operating system, and not part of the final application - Because all C++ applications can share it, by default the runtime is a separate installation.

In addition, each version of Visual C++ has its own runtime installer, because with each version there are slight differences and improvements in the way all this works. There are also different verisons of the runtime for different platforms (e.g. x86 and x64)

Hence, there are a number of "Visual Studio XXXX runtime installer (YYY)" downloads available from Microsoft, where the XXXX is the visual studio version (2005, 2008, 2010, etc), and YYY is usually "x86" or "x64".

Most applications that need the runtime will automatically install it if needed, so generally end-users are not very aware of these redistributables.