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C Run-Time Debug Libraries

The following table lists the debug versions of the C run-time library files, along with their associated compiler options and environment variables. For a list of the release versions of these libraries, see C Run-Time Libraries.

Prior to Visual C++ 4.2, the C run-time libraries contained the iostream library functions. In Visual C++ 4.2, the old iostream library functions were removed from LIBCD.LIB, LIBCMTD.LIB, and MSVCRTD.LIB. This change was made because the Standard C++ library was added to Visual C++, and it contains a new set of iostream libraries.

Two sets of iostream functions are now included in Visual C++. The old iostream functions now exist in their own libraries: LIBCID.LIB, LIBCIMTD.LIB, and MSVCIRTD.LIB. The new iostream functions, as well as many other new functions, exist in the Standard C++ libraries: LIBCPD.LIB, LIBCPMTD.LIB, and MSVCPRTD.LIB.

The Standard C++ library and the old iostream library are incompatible and only one of them can be linked with your project. See the Standard C++ Library Overview and Make the Old iostream Library the Default for details.

When you build a debug version of your project, one of the basic C run-time debug libraries (LIBCD.LIB, LIBCMTD.LIB, and MSVCRTD.LIB) is linked by default, depending on the compiler option you choose (single-threaded, multithreaded, or DLL). Depending on the headers you use in your code, a debug library from the Standard C++ libraries or one from the old iostream libraries may also be linked.

• If you include a Standard C++ library header in your code, a Standard C++ library will be linked in automatically by Visual C++ at compile time. For example:

   #include <ios> 

• If you include an old iostream library header, an old iostream library will be linked in automatically by Visual C++ at compile time. For example:

   #include <ios.h>

Note that headers from the Standard C++ library and the old iostream library cannot be mixed.

Headers determine whether a Standard C++ library, an old iostream library, or neither will be linked. Compiler options determine which of the libraries to be linked is the default (single-threaded, multithreaded, or DLL). When a specific library compiler option is defined, that library is considered to be the default and its environment variables are automatically defined.

C Run-Time Debug Library (without iostream) Characteristics Option Defined LIBCD.LIB Single-threaded, static link /MLd _DEBUG LIBCMTD.LIB Multithreaded, static link /MTd _DEBUG, _MT MSVCRTD.LIB Multithreaded, dynamic link
(import library for MSVCRTD.DLL)¹ /MDd _DEBUG, _MT, _DLL ¹   In place of the “x” in the DLL name, substitute the major version numeral of Visual C++ that you are using. For example, if you are using Visual C++ version 4, then the library name would be MSVCR40D.DLL.
Standard C++ Debug Library Characteristics Option Defined LIBCPD.LIB Single-threaded, static link /MLd _DEBUG LIBCPMTD.LIB Multithreaded, static link /MTd _DEBUG, _MT MSVCPRTD.LIB Multithreaded, dynamic link (import library for MSVCRTD.DLL) /MDd _DEBUG, _MT, _DLL
iostream Debug Library Characteristics Option Defined LIBCID.LIB Single threaded, static link /MLd _DEBUG LIBCIMTD.LIB Multithreaded, static link /MTd _DEBUG, _MT MSVCIRTD.LIB Multithreaded, dynamic link (import library for MSVCIRTD.DLL) /MDd _DEBUG, _MT, _DLL

The debug versions of the library functions differ from the release versions mainly in that debug information was included when they were compiled (using the /Z7 or /Zi compiler option), optimization was turned off, and source code is available. A few of the debug library functions also contain asserts that verify parameter validity.

Using one of these debug libraries is as simple as linking it to your application with the /DEBUG:FULL linker option set. You can then step directly into almost any run-time function call.

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