annotate new linkage info

Author: TylerMSFT

docs/c-runtime-library/reference/ctime-ctime32-ctime64-wctime-wctime32-wctime64.md

@@ -17,10 +17,10 @@ Convert a time value to a string and adjust for local time zone settings. More s
 ## Syntax
 
 ```C
-char *ctime( const time_t *sourceTime );
+char *ctime( const time_t *sourceTime ); // See note in remarks section about linkage
 char *_ctime32( const __time32_t *sourceTime );
 char *_ctime64( const __time64_t *sourceTime );
-wchar_t *_wctime( const time_t *sourceTime );
+wchar_t *_wctime( const time_t *sourceTime ); // See note in remarks section about linkage
 wchar_t *_wctime32( const __time32_t *sourceTime );
 wchar_t *_wctime64( const __time64_t *sourceTime );
 ```
@@ -62,6 +62,12 @@ These functions validate their parameters. If *`sourceTime`* is a null pointer,
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting with Windows SDK version 10.0.xxxxx.xxxx and Visual Studio 2026 or later, the following functions are no longer declared as `static inline` (internal linkage). Instead, they are now declared as `inline` (external linkage).\
+> To return to the previous behavior, `#define _STATIC_INLINE_UCRT_FUNCTIONS=1`before including any CRT headers. By default, `_STATIC_INLINE_UCRT_FUNCTIONS` is set to 0.\
+> This change increases UCRT conformance with the C++ standard, while also improving compatibility with C++ modules.\
+> This applies to the following functions: ctime, _wctime
+
 ### Generic-text routine mappings
 
 | TCHAR.H routine | `_UNICODE` and `_MBCS` not defined | `_MBCS` defined | `_UNICODE` defined |

docs/c-runtime-library/reference/ctime-s-ctime32-s-ctime64-s-wctime-s-wctime32-s-wctime64-s.md

@@ -16,7 +16,7 @@ Convert a time value to a string and adjust for local time zone settings. These
 ## Syntax
 
 ```C
-errno_t ctime_s(
+errno_t ctime_s( // See note in remarks section about linkage
    char* buffer,
    size_t numberOfElements,
    const time_t *sourceTime
@@ -31,7 +31,7 @@ errno_t _ctime64_s(
    size_t numberOfElements,
    const __time64_t *sourceTime
 );
-errno_t _wctime_s(
+errno_t _wctime_s( // See note in remarks section about linkage
    wchar_t* buffer,
    size_t numberOfElements,
    const time_t *sourceTime
@@ -124,6 +124,12 @@ The debug library versions of these functions first fill the buffer with 0xFE. T
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting with Windows SDK version 10.0.xxxxx.xxxx and Visual Studio 2026 or later, the following functions are no longer declared as `static inline` (internal linkage). Instead, they are now declared as `inline` (external linkage).\
+> To return to the previous behavior, `#define _STATIC_INLINE_UCRT_FUNCTIONS=1`before including any CRT headers. By default, `_STATIC_INLINE_UCRT_FUNCTIONS` is set to 0.\
+> This change increases UCRT conformance with the C++ standard, while also improving compatibility with C++ modules.\
+> This applies to the following functions: ctime_s, _wctime_s
+
 ### Generic-text routine mappings
 
 | TCHAR.H routine | `_UNICODE` and `_MBCS` not defined | `_MBCS` defined | `_UNICODE` defined |

docs/c-runtime-library/reference/difftime-difftime32-difftime64.md

@@ -17,7 +17,7 @@ Finds the difference between two times.
 ## Syntax
 
 ```C
-double difftime( time_t timeEnd, time_t timeStart );
+double difftime( time_t timeEnd, time_t timeStart ); // See note in remarks section about linkage
 double _difftime32( __time32_t timeEnd, __time32_t timeStart );
 double _difftime64( __time64_t timeEnd, __time64_t timeStart );
 ```
@@ -46,6 +46,13 @@ These functions validate their parameters. If either of the parameters is zero o
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting in Visual Studio 2025 and the Windows SDK 26000, this function changes from declaring the function (or functions for multi-function pages) with `static inline` to `inline`.\
+> You can opt-out of the change for your project by defining `_STATIC_INLINE_UCRT_FUNCTIONS=1`.\
+> You can adopt the change early by defining `_STATIC_INLINE_UCRT_FUNCTIONS=0`.\
+> This change improves conformance and helps avoid One Definition Rule (ODR) violations, especially when using modules.\
+> This applies to the following functions: difftime
+
 ## Requirements
 
 | Routine | Required header |

docs/c-runtime-library/reference/fstat-fstat32-fstat64-fstati64-fstat32i64-fstat64i32.md

@@ -16,7 +16,7 @@ Gets information about an open file.
 ## Syntax
 
 ```C
-int _fstat(
+int _fstat( // See note in remarks section about linkage
    int fd,
    struct _stat *buffer
 );
@@ -81,6 +81,12 @@ Unless `_USE_32BIT_TIME_T` is defined, **`_fstat`** is equivalent to **`_fstat64
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting with Windows SDK version 10.0.xxxxx.xxxx and Visual Studio 2026 or later, the following functions are no longer declared as `static inline` (internal linkage). Instead, they are now declared as `inline` (external linkage).\
+> To return to the previous behavior, `#define _STATIC_INLINE_UCRT_FUNCTIONS=1`before including any CRT headers. By default, `_STATIC_INLINE_UCRT_FUNCTIONS` is set to 0.\
+> This change increases UCRT conformance with the C++ standard, while also improving compatibility with C++ modules.\
+> This applies to the following functions: _fstat
+
 ### Time type and file length type variations of `_stat`
 
 | Functions | `_USE_32BIT_TIME_T` defined? | Time type | File length type |

docs/c-runtime-library/reference/ftime-ftime32-ftime64.md

@@ -17,7 +17,7 @@ Get the current time. More secure versions of these functions are available; see
 ## Syntax
 
 ```C
-void _ftime( struct _timeb *timeptr );
+void _ftime( struct _timeb *timeptr ); // See note in remarks section about linkage
 void _ftime32( struct __timeb32 *timeptr );
 void _ftime64( struct __timeb64 *timeptr );
 ```
@@ -46,6 +46,12 @@ The **`_ftime`** function is equivalent to **`_ftime64`**, and `_timeb` contains
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting with Windows SDK version 10.0.xxxxx.xxxx and Visual Studio 2026 or later, the following functions are no longer declared as `static inline` (internal linkage). Instead, they are now declared as `inline` (external linkage).\
+> To return to the previous behavior, `#define _STATIC_INLINE_UCRT_FUNCTIONS=1`before including any CRT headers. By default, `_STATIC_INLINE_UCRT_FUNCTIONS` is set to 0.\
+> This change increases UCRT conformance with the C++ standard, while also improving compatibility with C++ modules.\
+> This applies to the following functions: _ftime
+
 ## Requirements
 
 | Function | Required header |

docs/c-runtime-library/reference/futime-futime32-futime64.md

@@ -17,7 +17,7 @@ Sets the modification time on an open file.
 ## Syntax
 
 ```C
-int _futime(
+int _futime( // See note in remarks section about linkage
    int fd,
    struct _utimbuf *filetime
 );
@@ -51,6 +51,12 @@ The **`_futime`** routine sets the modification date and the access time on the
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting with Windows SDK version 10.0.xxxxx.xxxx and Visual Studio 2026 or later, the following functions are no longer declared as `static inline` (internal linkage). Instead, they are now declared as `inline` (external linkage).\
+> To return to the previous behavior, `#define _STATIC_INLINE_UCRT_FUNCTIONS=1`before including any CRT headers. By default, `_STATIC_INLINE_UCRT_FUNCTIONS` is set to 0.\
+> This change increases UCRT conformance with the C++ standard, while also improving compatibility with C++ modules.\
+> This applies to the following functions: _futime
+
 ## Requirements
 
 | Function | Required header | Optional header |

docs/c-runtime-library/reference/gmtime-gmtime32-gmtime64.md

@@ -16,7 +16,7 @@ Converts a `time_t` time value to a `tm` structure. More secure versions of thes
 ## Syntax
 
 ```C
-struct tm *gmtime( const time_t *sourceTime );
+struct tm *gmtime( const time_t *sourceTime ); // See note in remarks section about linkage
 struct tm *_gmtime32( const __time32_t *sourceTime );
 struct tm *_gmtime64( const __time64_t *sourceTime );
 ```
@@ -56,6 +56,13 @@ The **`_gmtime32`** function breaks down the *`sourceTime`* value and stores it
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting in Visual Studio 2025 and the Windows SDK 26000, this function changes from declaring the function (or functions for multi-function pages) with `static inline` to `inline`.\
+> You can opt-out of the change for your project by defining `_STATIC_INLINE_UCRT_FUNCTIONS=1`.\
+> You can adopt the change early by defining `_STATIC_INLINE_UCRT_FUNCTIONS=0`.\
+> This change improves conformance and helps avoid One Definition Rule (ODR) violations, especially when using modules.\
+> This applies to the following functions: gmtime
+
 ## Requirements
 
 | Routine | Required C header | Required C++ header |

docs/c-runtime-library/reference/gmtime-s-gmtime32-s-gmtime64-s.md

@@ -16,7 +16,7 @@ Converts a time value to a `tm` structure. These functions are versions of [`_gm
 ## Syntax
 
 ```C
-errno_t gmtime_s(
+errno_t gmtime_s( // See note in remarks section about linkage
    struct tm* tmDest,
    const __time_t* sourceTime
 );
@@ -76,6 +76,13 @@ Each of the structure fields is of type **`int`**, as shown in the following tab
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting in Visual Studio 2025 and the Windows SDK 26000, this function changes from declaring the function (or functions for multi-function pages) with `static inline` to `inline`.\
+> You can opt-out of the change for your project by defining `_STATIC_INLINE_UCRT_FUNCTIONS=1`.\
+> You can adopt the change early by defining `_STATIC_INLINE_UCRT_FUNCTIONS=0`.\
+> This change improves conformance and helps avoid One Definition Rule (ODR) violations, especially when using modules.\
+> This applies to the following functions: gmtime_s
+
 ## Requirements
 
 | Routine | Required C header | Required C++ header |

docs/c-runtime-library/reference/localtime-localtime32-localtime64.md

@@ -17,7 +17,7 @@ Converts a time value and corrects for the local time zone. More secure versions
 ## Syntax
 
 ```C
-struct tm *localtime( const time_t *sourceTime );
+struct tm *localtime( const time_t *sourceTime ); // See note in remarks section about linkage
 struct tm *_localtime32( const __time32_t *sourceTime );
 struct tm *_localtime64( const __time64_t *sourceTime );
 ```
@@ -72,6 +72,13 @@ These functions validate their parameters. If *`sourceTime`* is a null pointer,
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting in Visual Studio 2025 and the Windows SDK 26000, this function changes from declaring the function (or functions for multi-function pages) with `static inline` to `inline`.\
+> You can opt-out of the change for your project by defining `_STATIC_INLINE_UCRT_FUNCTIONS=1`.\
+> You can adopt the change early by defining `_STATIC_INLINE_UCRT_FUNCTIONS=0`.\
+> This change improves conformance and helps avoid One Definition Rule (ODR) violations, especially when using modules.\
+> This applies to the following functions: localtime
+
 ## Requirements
 
 | Routine | Required C header | Required C++ header |

docs/c-runtime-library/reference/localtime-s-localtime32-s-localtime64-s.md

@@ -17,7 +17,7 @@ Converts a **`time_t`** time value to a **`tm`** structure, and corrects for the
 ## Syntax
 
 ```C
-errno_t localtime_s(
+errno_t localtime_s( // See note in remarks section about linkage
    struct tm* const tmDest,
    time_t const* const sourceTime
 );
@@ -84,6 +84,13 @@ If the **`TZ`** environment variable is set, the C run-time library assumes rule
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).
 
+> [!Note]
+> Starting in Visual Studio 2025 and the Windows SDK 26000, this function changes from declaring the function (or functions for multi-function pages) with `static inline` to `inline`.\
+> You can opt-out of the change for your project by defining `_STATIC_INLINE_UCRT_FUNCTIONS=1`.\
+> You can adopt the change early by defining `_STATIC_INLINE_UCRT_FUNCTIONS=0`.\
+> This change improves conformance and helps avoid One Definition Rule (ODR) violations, especially when using modules.\
+> This applies to the following functions: localtime_s
+
 ## Requirements
 
 | Routine | Required C header | Required C++ header |