The **Time [sec, %]** column shows how long it took to compile each function in [wall clock responsibility time (WCTR)](https://devblogs.microsoft.com/cppblog/faster-cpp-builds-simplified-a-new-metric-for-time/#:~:text=Today%2C%20we%E2%80%99d%20like%20to%20teach%20you%20about%20a,your%20build%2C%20even%20in%20the%20presence%20of%20parallelism). This metric distributes the wall clock time among functions based on their use of parallel compiler threads. For example, if two different threads are compiling two different functions simultaneously within a one-second period, each function’s WCTR is recorded as 0.5 seconds. This reflects each function’s proportional share of the total compilation time, taking into account the resources each consumed during parallel execution. Thus, WCTR provides a better measure of the impact each function has on the overall build time in environments where multiple compilation activities occur simultaneously.

- You may see cases (like `Windows.h`) where the aggregated duration of all the times for a header file is longer than the duration of the entire build. What’s happening is that headers are being parsed on multiple threads at the same time. If two threads simultaneously spend one second parsing a header file, that's 2 seconds of build time even though only one second of wall clock time has gone by. For more information, see [wall clock responsibility time (WCTR)](https://devblogs.microsoft.com/cppblog/faster-cpp-builds-simplified-a-new-metric-for-time/#:~:text=Today%2C%20we%E2%80%99d%20like%20to%20teach%20you%20about%20a,your%20build%2C%20even%20in%20the%20presence%20of%20parallelism).

description: "Learn more about: /MD, /MT, /LD (Use Run-Time Library)"

title: "/MD, -MT, -LD (Use Run-Time Library)"

ms.date: "07/17/2019"

ms.assetid: cf7ed652-dc3a-49b3-aab9-ad60e5395579

Indicates whether a multithreaded module is a DLL and specifies retail or debug versions of the run-time library.

|**/MD**|Causes the application to use the multithread-specific and DLL-specific version of the run-time library. Defines `_MT` and `_DLL` and causes the compiler to place the library name MSVCRT.lib into the .obj file.|

|**/MDd**|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**|Causes the application to use the multithread, static version of the run-time library. 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**|Defines `_DEBUG` and `_MT`. This option 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.|

|**/LD**|Creates a DLL.<br /><br /> Passes the **/DLL** option to the linker. The linker looks for, but does not require, a `DllMain` function. If you do not write a `DllMain` function, the linker inserts a `DllMain` function that returns TRUE.<br /><br /> Links the DLL startup code.<br /><br /> Creates an import library (.lib), if an export (.exp) file is not specified on the command line. You link the import library to applications that call your DLL.<br /><br /> Interprets [/Fe (Name EXE File)](fe-name-exe-file.md) as naming a DLL rather than an .exe file. By default, the program name becomes *basename*.dll instead of *basename*.exe.<br /><br /> Implies **/MT** unless you explicitly specify **/MD**.|

|**/LDd**|Creates a debug DLL. Defines `_MT` and `_DEBUG`.|

For more information about C run-time libraries and which libraries are used when you compile with [/clr (Common Language Runtime Compilation)](clr-common-language-runtime-compilation.md), see [CRT Library Features](../../c-runtime-library/crt-library-features.md).

All modules passed to a given invocation of the linker must have been compiled with the same run-time library compiler option (**/MD**, **/MT**, **/LD**).

For more information about how to use the debug versions of the run-time libraries, see [C Run-Time Library Reference](../../c-runtime-library/c-run-time-library-reference.md).

[MSVC Compiler Options](compiler-options.md)<br/>

[MSVC Compiler Command-Line Syntax](compiler-command-line-syntax.md)

helpviewer_keywords:

void main() {

// Missing side effect annotation _Acquires_lock_(&p->cs)

// Missing side effect annotation _Releases_lock_(&p->cs)

description: "Learn more about: Warning C6387"

ms.assetid: 3ea2fc4d-ffc3-4c3c-bfae-d42aa56235d8

void main()

description: "Learn more about: Warning C6394"

This rule is enforced by checking if a lookup table has an initial size of 365 elements, but can be expanded to 366. However, it doesn't check if the table’s size is adjusted through proper leap year check or not, and so is a low confidence warning.

description: "Learn more about: Fundamental types (C++/CX)"

ms.assetid: c9f82907-25f2-440b-91d6-afb8dbd46ea6

In addition to the standard C++ built-in types, C++/CX supports the type system that's defined by the Windows Runtime architecture by providing typedefs for the Windows Runtime fundamental types that map to standard C++ types.. C++/CX implements Boolean, character, and numeric fundamental types. These typedefs are defined in the `default` namespace, which never needs to be specified explicitly. In addition, C++/CX provides wrappers and concrete implementations for certain Windows Runtime types and interfaces.

| `cpp_include_cleanup_excluded_files`</br></br>Excludes the specified files from Include Cleanup messages. You won’t get a suggestion related to the header at all, whether to add it or that it's unused. | *filename* | `cpp_include_cleanup_excluded_files = vcruntime.h, vcruntime_string.h` |