Updates to documentation for string printf functions

docs/c-runtime-library/reference/snprintf-s-snprintf-s-l-snwprintf-s-snwprintf-s-l.md

@@ -84,14 +84,33 @@ The locale to use.
 
 ## Return Value
 
-**`_snprintf_s`** returns the number of characters stored in *`buffer`*, not counting the terminating null character. **`_snwprintf_s`** returns the number of wide characters stored in *`buffer`*, not counting the terminating null wide character.
+**`_snprintf_s`** and **`_snwprintf_s`** return the number of characters written, not including the terminating null, or a negative value if truncation of the data occurs (for **`_snwprintf_s`**, this is a count of wide characters). If an encoding error occurs during formatting, the invalid parameter handler is invoked — as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
 
-If the storage required to store the data and a terminating null exceeds *`sizeOfBuffer`*, the invalid parameter handler is invoked, as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution continues after the invalid parameter handler, these functions set *`buffer`* to an empty string, set **`errno`** to **`ERANGE`**, and return -1.
+* If *`count`* is less than *`sizeOfBuffer`* and the number of characters of data is less than or equal to *`count`*, or *`count`* is [`_TRUNCATE`](../../c-runtime-library/truncate.md) and the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written, a terminating null is appended and the number of characters is returned.
 
-If *`buffer`* or *`format`* is a **`NULL`** pointer, or if *`count`* is less than or equal to zero, the invalid parameter handler is invoked. If execution is allowed to continue, these functions set **`errno`** to **`EINVAL`** and return -1.
+* If *`count`* is less than *`sizeOfBuffer`* but the data exceeds *`count`* characters, then the first *`count`* characters are written. Truncation of the remaining data occurs and -1 is returned without invoking the invalid parameter handler.
+
+* If *`count`* is [`_TRUNCATE`](../../c-runtime-library/truncate.md) and the number of characters of data equals or exceeds *`sizeOfBuffer`*, then as much of the string as will fit in *`buffer`* (with terminating null) is written. Truncation of the remaining data occurs and -1 is returned without invoking the invalid parameter handler.
+
+* If *`count`* is greater than or equal to *`sizeOfBuffer`* but the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written (with terminating null) and the number of characters is returned.
+
+* If *`count`* and the number of characters of data both equal or exceed *`sizeOfBuffer`* (and *`count`* is not [`_TRUNCATE`](../../c-runtime-library/truncate.md)), the invalid parameter handler is invoked — as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution continues after the invalid parameter handler, these functions set *buffer* to an empty string, set **`errno`** to **`ERANGE`**, and return -1.
+
+* If *`buffer`* is a **`NULL`** pointer and both *`sizeOfBuffer`* and *`count`* are equal to zero, these functions return 0.
+
+* If *`format`* is a **`NULL`** pointer, or *`buffer`* is a **`NULL`** pointer and either *`sizeOfBuffer`* or *`count`* are nonzero, or if *`buffer`* is not a **`NULL`** pointer and *`sizeOfBuffer`* is zero, the invalid parameter handler is invoked. If execution is allowed to continue, these functions set **`errno`** to **`EINVAL`** and return -1.
 
 For information about these and other error codes, see [`_doserrno`, `errno`, `_sys_errlist`, and `_sys_nerr`](../../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md).
 
+### Error Conditions
+
+|**Condition**|Return|**`errno`**|
+|-----------------|------------|-------------|
+|*`buffer`* is **`NULL`** (and either *`sizeOfBuffer`* or *`count`* != 0)|-1|**`EINVAL`**|
+|*`format`* is **`NULL`**|-1|**`EINVAL`**|
+|*`buffer`* != **`NULL`** and *`sizeOfBuffer`* == 0|-1|**`EINVAL`**|
+|*`sizeOfBuffer`* too small (and *`count`* != **`_TRUNCATE`**)|-1 (and *`buffer`* set to an empty string)|**`ERANGE`**|
+
 ## Remarks
 
 The **`_snprintf_s`** function formats and stores *`count`* or fewer characters in *`buffer`* and appends a terminating null. Each argument (if any) is converted and output according to the corresponding format specification in *`format`*. The formatting is consistent with the **`printf`** family of functions; see [Format Specification Syntax: `printf` and `wprintf` Functions](../../c-runtime-library/format-specification-syntax-printf-and-wprintf-functions.md). If copying occurs between strings that overlap, the behavior is undefined.

docs/c-runtime-library/reference/snprintf-snprintf-snprintf-l-snwprintf-snwprintf-l.md

@@ -101,19 +101,21 @@ For more information, see [Format Specification Syntax: `printf` and `wprintf` F
 
 ## Return Value
 
-Let **`len`** be the length of the formatted data string, not including the terminating null. Both **`len`** and **`count`** are the number of characters for **`snprintf`** and **`_snprintf`**, and the number of wide characters for **`_snwprintf`**.
+Let **`len`** be the length of the formatted data string, not including the terminating null. Both **`len`** and *`count`* are the number of characters for **`snprintf`** and **`_snprintf`**, and the number of wide characters for **`_snwprintf`**.
 
-For all functions, if **`len`** < *`count`*, **`len`** characters are stored in *`buffer`*, a null-terminator is appended, and **`len`** is returned.
+For all functions, if an encoding error occurs during formatting, the invalid parameter handler is invoked &mdash; as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
+
+For all functions, if *`buffer`* is **`NULL`** and *`count`* is zero, **`len`** is returned as the count of characters required to format the output &mdash; not including the terminating null. To make a successful call with the same *`argument`* and *`locale`* parameters, allocate a buffer holding at least **`len`** + 1 characters.
 
-The **`snprintf`** function truncates the output when **`len`** is greater than or equal to *`count`*, by placing a null-terminator at `buffer[count-1]`. The value returned is **`len`**, the number of characters that would have been output if *`count`* was large enough. The **`snprintf`** function returns a negative value if an encoding error occurs.
+For all functions, if **`len`** < *`count`*, **`len`** characters are stored in *`buffer`*, a null-terminator is appended, and **`len`** is returned.
 
-For all functions other than **`snprintf`**, if **`len`** = *`count`*, **`len`** characters are stored in *`buffer`*, no null-terminator is appended, and **`len`** is returned. If **`len`** > *`count`*, *`count`* characters are stored in *`buffer`*, no null-terminator is appended, and a negative value is returned.
+The **`snprintf`** function truncates the output when *`count`* is nonzero and **`len`** >= *`count`*, by placing a null-terminator at `buffer[count-1]` (when *`count`* is zero, no characters are stored in *`buffer`* &mdash; whether it is **`NULL`** or not). In all cases where **`len`** >= *`count`*, the value returned by the **`snprintf`** function is **`len`** (the number of characters that would have been output if *`count`* was large enough). As a corollary, if **`snprintf`** returns a value > *`count`* - 1, the output has been truncated.
 
-If *`buffer`* is a null pointer and *`count`* is zero, **`len`** is returned as the count of characters required to format the output, not including the terminating null. To make a successful call with the same *`argument`* and *`locale`* parameters, allocate a buffer holding at least **`len`** + 1 characters.
+For all functions other than **`snprintf`**, if **`len`** = *`count`*, **`len`** characters are stored in *`buffer`*, no null-terminator is appended, and **`len`** is returned. If **`len`** > *`count`* and *`buffer`* is not **`NULL`**, *`count`* characters are stored in *`buffer`*, no null-terminator is appended, and a negative value is returned.
 
-If *`buffer`* is a null pointer and *`count`* is nonzero, or if *`format`* is a null pointer, the invalid parameter handler is invoked, as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
+If *`buffer`* is **`NULL`** and *`count`* is nonzero, or if *`format`* is **`NULL`**, the invalid parameter handler is invoked &mdash; as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
 
-For information about these and other error codes, see [`errno`, `_doserrno`, `_sys_errlist, and `_sys_nerr`](../../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md).
+For information about these and other error codes, see [`errno`, `_doserrno`, `_sys_errlist`, and `_sys_nerr`](../../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md).
 
 ## Remarks
 

docs/c-runtime-library/reference/vsnprintf-s-vsnprintf-s-vsnprintf-s-l-vsnwprintf-s-vsnwprintf-s-l.md

@@ -93,27 +93,29 @@ For more information, see [Format Specifications](../../c-runtime-library/format
 
 ## Return Value
 
-**`vsnprintf_s`**, **`_vsnprintf_s`** and **`_vsnwprintf_s`** return the number of characters written, not including the terminating null, or a negative value if either truncation of the data or an output error occurs.
+**`vsnprintf_s`**, **`_vsnprintf_s`** and **`_vsnwprintf_s`** return the number of characters written, not including the terminating null, or a negative value if truncation of the data occurs (for **`_vsnwprintf_s`**, this is a count of wide characters). If an encoding error occurs during formatting, the invalid parameter handler is invoked — as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
 
-* If *`count`* is less than *`sizeOfBuffer`* and the number of characters of data is less than or equal to *`count`*, or *`count`* is [`_TRUNCATE`](../../c-runtime-library/truncate.md) and the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written and the number of characters is returned.
+* If *`count`* is less than *`sizeOfBuffer`* and the number of characters of data is less than or equal to *`count`*, or *`count`* is [`_TRUNCATE`](../../c-runtime-library/truncate.md) and the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written, a terminating null is appended and the number of characters is returned.
 
 * If *`count`* is less than *`sizeOfBuffer`* but the data exceeds *`count`* characters, then the first *`count`* characters are written. Truncation of the remaining data occurs and -1 is returned without invoking the invalid parameter handler.
 
 * If *`count`* is [`_TRUNCATE`](../../c-runtime-library/truncate.md) and the number of characters of data equals or exceeds *`sizeOfBuffer`*, then as much of the string as will fit in *`buffer`* (with terminating null) is written. Truncation of the remaining data occurs and -1 is returned without invoking the invalid parameter handler.
 
-* If *`count`* is equal to or exceeds *`sizeOfBuffer`* but the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written (with terminating null) and the number of characters is returned.
+* If *`count`* is greater than or equal to *`sizeOfBuffer`* but the number of characters of data is less than *`sizeOfBuffer`*, then all of the data is written (with terminating null) and the number of characters is returned.
 
-* If *`count`* and the number of characters of data both equal or exceed *`sizeOfBuffer`*, the invalid parameter handler is invoked, as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution continues after the invalid parameter handler, these functions set *buffer* to an empty string, set **`errno`** to **`ERANGE`**, and return -1.
+* If *`count`* and the number of characters of data both equal or exceed *`sizeOfBuffer`* (and *`count`* is not [`_TRUNCATE`](../../c-runtime-library/truncate.md)), the invalid parameter handler is invoked — as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution continues after the invalid parameter handler, these functions set *buffer* to an empty string, set **`errno`** to **`ERANGE`**, and return -1.
 
-* If *`buffer`* or *`format`* is a **`NULL`** pointer, or if *`count`* is less than or equal to zero, the invalid parameter handler is invoked. If execution is allowed to continue, these functions set **`errno`** to **`EINVAL`** and return -1.
+* If *`buffer`* is a **`NULL`** pointer and both *`sizeOfBuffer`* and *`count`* are equal to zero, these functions return 0.
+
+* If *`format`* is a **`NULL`** pointer, or *`buffer`* is a **`NULL`** pointer and either *`sizeOfBuffer`* or *`count`* are nonzero, or if *`buffer`* is not a **`NULL`** pointer and *`sizeOfBuffer`* is zero, the invalid parameter handler is invoked. If execution is allowed to continue, these functions set **`errno`** to **`EINVAL`** and return -1.
 
 ### Error Conditions
 
 |**Condition**|Return|**`errno`**|
 |-----------------|------------|-------------|
-|*`buffer`* is **`NULL`**|-1|**`EINVAL`**|
+|*`buffer`* is **`NULL`** (and either *`sizeOfBuffer`* or *`count`* != 0)|-1|**`EINVAL`**|
 |*`format`* is **`NULL`**|-1|**`EINVAL`**|
-|*`count`* <= 0|-1|**`EINVAL`**|
+|*`buffer`* != **`NULL`** and *`sizeOfBuffer`* == 0|-1|**`EINVAL`**|
 |*`sizeOfBuffer`* too small (and *`count`* != **`_TRUNCATE`**)|-1 (and *`buffer`* set to an empty string)|**`ERANGE`**|
 
 ## Remarks

docs/c-runtime-library/reference/vsnprintf-vsnprintf-vsnprintf-l-vsnwprintf-vsnwprintf-l.md

@@ -104,19 +104,25 @@ Pointer to list of arguments.
 *`locale`*<br/>
 The locale to use.
 
-For more information, see [Format Specifications](../../c-runtime-library/format-specification-syntax-printf-and-wprintf-functions.md).
+For more information, see [Format Specification Syntax: `printf` and `wprintf` Functions](../../c-runtime-library/format-specification-syntax-printf-and-wprintf-functions.md).
 
 ## Return Value
 
-The **`vsnprintf`** function returns the number of characters that are written, not counting the terminating null character. If the buffer size specified by *`count`* isn't sufficiently large to contain the output specified by *`format`* and *`argptr`*, the return value of **`vsnprintf`** is the number of characters that would be written, not counting the null character, if *`count`* were sufficiently large. If the return value is greater than *`count`* - 1, the output has been truncated. A return value of -1 indicates that an encoding error has occurred.
+Let **`len`** be the length of the formatted data string specified by *`format`* and *`argptr`*, not including the terminating null. Both **`len`** and *`count`* are the number of characters for **`vsnprintf`** and **`_vsnprintf`**, and the number of wide characters for **`_vsnwprintf`**.
 
-Both **`_vsnprintf`** and **`_vsnwprintf`** functions return the number of characters written if the number of characters to write is less than or equal to *`count`*. If the number of characters to write is greater than *`count`*, these functions return -1 indicating that output has been truncated.
+For all functions, if an encoding error occurs during formatting, the invalid parameter handler is invoked &mdash; as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
 
-The value returned by all these functions doesn't include the terminating null, whether one is written or not.
+For all functions, if *`buffer`* is **`NULL`** and *`count`* is zero, **`len`** is returned as the count of characters required to format the output &mdash; not including the terminating null. To make a successful call with the same *`argument`* and *`locale`* parameters, allocate a buffer holding at least **`len`** + 1 characters.
 
-- If *`count`* is zero and *`buffer`* is **`NULL`**, the value returned is the number of characters the functions would write. The value does not take into account a terminating **`NULL`**. You can use this result to allocate sufficient buffer space for the string and its terminating null, and then call the function again to fill the buffer.
-- If *`count`* is zero but *`buffer`* isn't **`NULL`**, nothing is written and the function returns `-1`.
-- If *`format`* is **`NULL`**, or if *`buffer`* is **`NULL`** and *count* isn't equal to zero, these functions invoke the invalid parameter handler, as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
+For all functions, if **`len`** < *`count`*, **`len`** characters are stored in *`buffer`*, a null-terminator is appended, and **`len`** is returned.
+
+The **`vsnprintf`** function truncates the output when *`count`* is nonzero and **`len`** >= *`count`*, by placing a null-terminator at `buffer[count-1]` (when *`count`* is zero, no characters are stored in *`buffer`* &mdash; whether it is **`NULL`** or not). In all cases where **`len`** >= *`count`*, the value returned by the **`vsnprintf`** function is **`len`** (the number of characters that would have been output if *`count`* was large enough). As a corollary, if **`vsnprintf`** returns a value > *`count`* - 1, the output has been truncated.
+
+For all functions other than **`vsnprintf`**, if **`len`** = *`count`*, **`len`** characters are stored in *`buffer`*, no null-terminator is appended, and **`len`** is returned. If **`len`** > *`count`* and *`buffer`* is not **`NULL`**, *`count`* characters are stored in *`buffer`*, no null-terminator is appended, and a negative value is returned.
+
+If *`buffer`* is **`NULL`** and *`count`* is nonzero, or if *`format`* is **`NULL`**, the invalid parameter handler is invoked &mdash; as described in [Parameter Validation](../../c-runtime-library/parameter-validation.md). If execution is allowed to continue, these functions return -1 and set **`errno`** to **`EINVAL`**.
+
+For information about these and other error codes, see [`errno`, `_doserrno`, `_sys_errlist`, and `_sys_nerr`](../../c-runtime-library/errno-doserrno-sys-errlist-and-sys-nerr.md).
 
 ## Remarks