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title description ms.date author ms.author f1_keywords helpviewer_keywords
/exportHeader (Create header units)
Use the /exportHeader compiler option to create module header units for the header-name or include files specified.
05/18/2020
tylermsft
twhitney
/exportHeader
/exportHeader
Create header units

/exportHeader (Create header units)

Tells the compiler to create the header units specified by the input arguments. The compiler generates header units as IFC (.ifc) files.

Syntax

/exportHeader /headerName:angle header-name
/exportHeader /headerName:quote header-name
/exportHeader full path to header file

Arguments

The argument to /exportHeader is a /headerName command-line option that specifies the name, header-name, of the header file to export.

Remarks

/exportHeader is available starting in Visual Studio 2019 version 16.10.

The /exportHeader compiler option requires you enable the /std:c++20 or later compiler option (such as /std:c++latest).

One /exportHeader compiler option can specify as many header-name arguments as your build requires. You don't need to specify them separately.

The compiler implicitly enables the new preprocessor when this option is used. That is, /Zc:preprocessor is added to the command line by the compiler if any form of /exportHeader is used on the command line. To opt out of the implicit /Zc:preprocessor, use: /Zc:preprocessor-

By default, the compiler doesn't produce an object file when a header unit is compiled. To produce an object file, specify the /Fo compiler option. For more information, see /Fo (Object File Name).

You may find it helpful to use the complementary option /showResolvedHeader. The /showResolvedHeader option prints an absolute path to the file the header-name argument resolves to.

/exportHeader can handle multiple inputs at once, even under /MP. We recommended you use /ifcOutput <directory> to create a separate .ifc file for each compilation.

Examples

To build a header unit such as <vector> might look like:

cl . . . /std:c++latest /exportHeader /headerName:angle vector

Building a local project header such as "utils/util.h" might look like:

cl . . . /std:c++latest /exportHeader /headerName:quote util/util.h

To set this compiler option in the Visual Studio development environment

You normally shouldn't set this option in the Visual Studio development environment unless you use a different extension for your header files. By default, the build system applies this option to compiled files that have a .h extension, or no extension.

  1. To apply the /exportHeader option to a file explicitly in the IDE, select the file in Solution Explorer. Right-click to open the context menu and select Properties to open the Property Pages dialog.

  2. Set the Configuration dropdown to All Configurations. Set the Platform dropdown to All Platforms.

  3. Open the Configuration Properties > C/C++ > Advanced property page.

  4. Use the dropdown control to modify the Compile As property to Compile as C++ Header Unit (/exportHeader). Choose OK or Apply to save your changes.

See also

/headerName (Build a header unit from the specified header)
/headerUnit (Use header unit IFC)
/reference (Use named module IFC)
/translateInclude (Translate include directives into import directives)