bug fix: 1536384 note implicit compiler flag that is set when using header units. Also, update how null is specified.

TylerMSFT · TylerMSFT · commit 711ceafe3d05 · 2022-05-09T11:10:18.000-07:00
diff --git a/docs/build/walkthrough-header-units.md b/docs/build/walkthrough-header-units.md
@@ -1,7 +1,7 @@
 ---
 description: "Learn more about C++ header units. Convert a header file to a header unit using Visual Studio 2022."
 title: "Walkthrough: Build and import header units in Visual C++ projects"
-ms.date: 02/04/2022
+ms.date: 05/09/2022
 ms.custom: "conceptual"
 author: "tylermsft"
 ms.author: "twhitney"
@@ -143,6 +143,14 @@ These features are designed for legacy code. For new code, move to modules inste
 
 For an example of how this technique is used to import STL header files as header units, see [Walkthrough: Import STL libraries as header units](walkthrough-import-stl-header-units.md#approach2).
 
+## Compiler flag side effects
+
+The compiler implicitly enables the new C99 and C++11 conforming preprocessor when compiling header units. That is, [`/Zc:preprocessor`](/cpp/build/reference/zc-preprocessor) is added to the command line by the compiler if any form of `/exportHeader` is used.
+
+Enabling the new preprocessor affects processing variadic macros. See the remarks section of [Variadic macros](/cpp/preprocessor/variadic-macros#remarks) for details.
+
+To opt out of the implicit `/Zc:preprocessor`, add `/Zc:preprocessor-` to the command line switches to use the traditional (non-conforming) preprocessor.
+
 ## See also
 
 [`/translateInclude`](./reference/translateinclude.md)\
diff --git a/docs/text/how-to-convert-between-various-string-types.md b/docs/text/how-to-convert-between-various-string-types.md
@@ -2,7 +2,7 @@
 description: "Learn more about: How to: Convert Between Various String Types"
 title: "How to: Convert Between Various String Types"
 ms.custom: "get-started-article"
-ms.date: 05/04/2022
+ms.date: 05/09/2022
 helpviewer_keywords: ["converting string types", "string conversion [C++]", "strings [C++], converting"]
 ---
 # How to: Convert between various string types
@@ -40,7 +40,7 @@ The `/clr` switch conflicts with some compiler switches that are set when you cr
 
 ### Description
 
-This example demonstrates how to convert from a `char *` to the string types listed above. A `char *` string (also known as a C-style string) uses a null character to indicate the end of the string. C-style strings usually require 1 byte per character, but can also use 2 bytes. In the examples below, `char *` strings are sometimes referred to as multibyte character strings because of the string data that results from converting from wide Unicode strings. Single byte and multibyte character (`MBCS`) functions can operate on `char *` strings.
+This example demonstrates how to convert from a `char *` to the string types listed above. A `char *` string (also known as a C-style string) uses a terminating null to indicate the end of the string. C-style strings usually require 1 byte per character, but can also use 2 bytes. In the examples below, `char *` strings are sometimes referred to as multibyte character strings because of the string data that results from converting from wide Unicode strings. Single byte and multibyte character (`MBCS`) functions can operate on `char *` strings.
 
 For information about running and debugging this example, see [Run the examples](#run-the-examples).
 
@@ -267,7 +267,7 @@ Hello, World! (System::String)
 
 ### Description
 
-This example demonstrates how to convert from a `_bstr_t` to other string types. The `_bstr_t` object encapsulates wide character `BSTR` strings. A `BSTR` string has a length value and doesn't use a null character to terminate the string, but the string type you convert to may require a terminating `NULL`.
+This example demonstrates how to convert from a `_bstr_t` to other string types. The `_bstr_t` object encapsulates wide character `BSTR` strings. A `BSTR` string has a length value and doesn't use a null character to terminate the string, but the string type you convert to may require a terminating null character.
 
 For information about running and debugging this example, see [Run the examples](#run-the-examples).
 ### Code
@@ -296,7 +296,7 @@ int main()
 
     // Convert the wide character _bstr_t string to a C-style
     // string. To be safe, allocate two bytes for each character
-    // in the char* string, including the terminating NULL.
+    // in the char* string, including the terminating null.
     const size_t newsize = (orig.length() + 1) * 2;
     char* nstring = new char[newsize];
 
@@ -368,7 +368,7 @@ Hello, World! (System::String)
 
 ### Description
 
-This example demonstrates how to convert from a `CComBSTR` to other string types. Like `_bstr_t`, a `CComBSTR` object encapsulates wide character `BSTR` strings. A `BSTR` string has a length value and doesn't use a null character to terminate the string, but the string type you convert to may require a terminating `NULL`.
+This example demonstrates how to convert from a `CComBSTR` to other string types. Like `_bstr_t`, a `CComBSTR` object encapsulates wide character `BSTR` strings. A `BSTR` string has a length value and doesn't use a null character to terminate the string, but the string type you convert to may require a terminating null.
 
 For information about running and debugging this example, see [Run the examples](#run-the-examples).
 
@@ -403,7 +403,7 @@ int main()
     // Convert a wide character CComBSTR string to a
     // regular multibyte char* string. Allocate enough space
     // in the new string for the largest possible result,
-    // including space for a terminating NULL.
+    // including space for a terminating null.
     const size_t newsize = (orig.Length() + 1) * 2;
     char* nstring = new char[newsize];
 
@@ -657,7 +657,7 @@ int main()
 
     // Convert a wide character basic_string string to a multibyte char*
     // string. To be safe, we allocate two bytes for each character
-    // in the original string, including the terminating NULL.
+    // in the original string, including the terminating null.
     const size_t newsize = (orig.size() + 1) * 2;
 
     char* nstring = new char[newsize];
@@ -765,7 +765,7 @@ int main()
     // Make a copy of the System::String as a multibyte
     // char* string. Allocate two bytes in the multibyte
     // output string for every wide character in the input
-    // string, including space for a terminating NULL.
+    // string, including space for a terminating null.
     size_t origsize = wcslen(wch) + 1;
     const size_t newsize = origsize * 2;
     size_t convertedChars = 0;
