Treat the rest of the file as external for diagnostics reports.

#pragma system_header

The system_header pragma tells the compiler to show diagnostics at the level specified by the /external:Wn option for the rest of the current source file. For more information on how to specify external files and the external warning level to the compiler, see /external.

The system_header pragma doesn't apply past the end of the current source file. In other words, it doesn't apply to files that include this file. The system_header pragma applies even if no other files are specified as external to the compiler. However, if no /external:Wn option level is specified, the compiler may issue a diagnostic and uses the same warning level it applies to non-external files. Other pragma directives that affect warning behavior still apply after a system_header pragma. The effect of #pragma system_header is similar to the warning pragma:

// If n represents the warning level specified by /external:Wn,
// #pragma system_header is roughly equivalent to:
#pragma warning( push, n )

// . . .

// At the end of the file:
#pragma warning( pop )

The system_header pragma is available starting in Visual Studio 2019 version 16.10.

This sample header shows how to mark the contents of a file as external:

// library.h
// Use /external:Wn to set the compiler diagnostics level for this file's contents

#pragma once
#ifndef _LIBRARY_H // include guard for 3rd party interop
#define _LIBRARY_H
#pragma system_header
// The compiler applies the /external:Wn diagnostic level from here to the end of this file.

// . . .

// You can still override the external diagnostic level for warnings locally:
#pragma warning( push )
#pragma warning( error : 4164 )

// . . .

#pragma warning(pop)

// . . .

#endif

/external
warning pragma
/Wn (Compiler warning level)
Pragma directives and the __pragma and _Pragma keywords