Add note about _CRT_DECLARE_NONSTDC_NAMES
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With `/c11` and `/c17` properly defining `__STDC__`, users may encounter that the POSIX functions they are relying on are no longer exposed. This was always the case with `/Za` but is now also visible with the standard C versions.
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colin-home
approved these changes
Jan 19, 2022
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Oops, I missed the part about 17.2. We'll fix it in post. Although I note the flag has been around a long time and already guarded the POSIX typedefs and defined macros. Also, we recommend Microsoft people use the private repo, cpp-docs-pr, for their contributions, since it does additional build validations and also lets us embargo content for release. |
amyw-msft
reviewed
Jan 19, 2022
| @@ -20,7 +20,7 @@ The UCRT also implements a large subset of the POSIX.1 (ISO/IEC 9945-1:1996, the | |||
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| Functions specific to the Microsoft implementation of Visual C++ are found in the vcruntime library. Many of these functions are for internal use and can't be called by user code. Some are documented for use in debugging and implementation compatibility. | |||
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| The C++ standard reserves names that begin with an underscore in the global namespace to the implementation. Both the POSIX functions and Microsoft-specific runtime library functions are in the global namespace, but aren't part of the standard C runtime library. That's why the preferred Microsoft implementations of these functions have a leading underscore. For portability, the UCRT also supports the default names, but the Microsoft C++ compiler issues a deprecation warning when code that uses them is compiled. Only the default names are deprecated, not the functions themselves. To suppress the warning, define `_CRT_NONSTDC_NO_WARNINGS` before including any headers in code that uses the original POSIX names. | |||
| The C++ standard reserves names that begin with an underscore in the global namespace to the implementation. Both the POSIX functions and Microsoft-specific runtime library functions are in the global namespace, but aren't part of the standard C runtime library. That's why the preferred Microsoft implementations of these functions have a leading underscore. For portability, the UCRT also supports the default names, but the Microsoft C++ compiler issues a deprecation warning when code that uses them is compiled. Only the default names are deprecated, not the functions themselves. To suppress the warning, define `_CRT_NONSTDC_NO_WARNINGS` before including any headers in code that uses the original POSIX names. Because the C standard doesn't allow non-standard names in header files, by default [`/std:c11`](../build/reference/std-specify-language-standard-version.md) and [`/std:c17`](../build/reference/std-specify-language-standard-version.md) don't expose the default names for POSIX functions, types, and macros. If these names are necessary, define `_CRT_DECLARE_NONSTDC_NAMES` to expose them. | |||
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If these names are necessary, define
_CRT_DECLARE_NONSTDC_NAMESto expose them.
This is actually an on/off switch. Defining that macro to 1 will enable the default names and defining that macro to 0 will disable the default names, regardless of the /std or /Za setting.
Xazax-hun
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to Xazax-hun/cpp-docs
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Feb 23, 2022
add debugInfo macro definitions
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With
/c11and/c17properly defining__STDC__, users may encounter that the POSIX functions they are relying on are no longer exposed. This was always the case with/Zabut is now also visible with the standard C versions.Gated by 17.2 preview 2 at the earliest.