Visual Studio #

Compiler Options #

In Microsoft Visual Studio compiler, /MD, /MDd, /MT, and /MTd are options that determine which version of the C++ runtime library to use. Here’s what each of them means:

/MD: This option causes the application to use the multithread-specific and DLL-specific version of the run-time library. It defines _MT and _DLL and causes the compiler to place the library name MSVCRT.lib into the .obj file. Applications compiled with this option are statically linked to MSVCRT.lib. The actual working code is contained in MSVCR versionnumber .DLL, which must be available at run time to applications linked with MSVCRT.lib.
/MDd: This option defines _DEBUG, _MT, and _DLL and causes the application to use the debug multithread-specific and DLL-specific version of the run-time library. It also causes the compiler to place the library name MSVCRTD.lib into the .obj file.
/MT: This option causes the application to use the multithread, static version of the run-time library. It defines _MT and causes the compiler to place the library name LIBCMT.lib into the .obj file so that the linker will use LIBCMT.lib to resolve external symbols.
/MTd: This option defines _DEBUG and _MT. It also causes the compiler to place the library name LIBCMTD.lib into the .obj file so that the linker will use LIBCMTD.lib to resolve external symbols.

In general, if you are using DLLs, you should go for the dynamically linked CRT (/MD). Either /MT or /MD (or their debug equivalents /MTd or /MDd) is required to create multithreaded programs.