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StringCbCatNExW function (strsafe.h)

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Concatenates the specified number of bytes from one string to another string. The size of the destination buffer is provided to the function to ensure that it does not write past the end of this buffer.

StringCbCatNEx is a replacement for the following functions:

StringCbCatNEx adds to the functionality of StringCbCatN by returning a pointer to the end of the destination string as well as the number of bytes left unused in that string. Flags may also be passed to the function for additional control.

Syntax

STRSAFEAPI StringCbCatNExW(
  [in, out]       STRSAFE_LPWSTR  pszDest,
  [in]            size_t          cbDest,
  [in]            STRSAFE_PCNZWCH pszSrc,
  [in]            size_t          cbToAppend,
  [out, optional] STRSAFE_LPWSTR  *ppszDestEnd,
  [out, optional] size_t          *pcbRemaining,
  [in]            DWORD           dwFlags
);

Parameters

[in, out] pszDest

Type: LPTSTR

The destination buffer, which contains the string that is to be concatenated with pszSrc, and will receive the entire resultant string. The string at pszSrc is added to the end of the string at pszDest.

[in] cbDest

Type: size_t

The size of the destination buffer, in bytes. This value must consider the length of pszSrc plus the length of pszDest plus the bytes used for the terminating null character. The maximum number of bytes allowed is STRSAFE_MAX_CCH * sizeof(TCHAR).

[in] pszSrc

Type: LPCTSTR

The source string that is to be concatenated to the end of pszDest. This string must be null-terminated.

[in] cbToAppend

Type: size_t

The maximum number of bytes to append to pszDest.

[out, optional] ppszDestEnd

Type: LPTSTR*

The address of a pointer to the end of pszDest. If ppszDestEnd is non-NULL and any data is appended to the destination buffer, this points to the terminating null character at the end of the string.

[out, optional] pcbRemaining

Type: size_t*

The number of unused bytes in pszDest, including those used for the terminating null character. If pcbRemaining is NULL, the count is not kept or returned.

[in] dwFlags

Type: DWORD

One or more of the following values.

Value Meaning
STRSAFE_FILL_BEHIND_NULL
0x00000200
 If the function succeeds, the low byte of dwFlags (0) is used to fill the uninitialized portion of pszDest following the terminating null character.
STRSAFE_IGNORE_NULLS
0x00000100
 Treat NULL string pointers like empty strings (TEXT("")).
STRSAFE_FILL_ON_FAILURE
0x00000400
 If the function fails, the low byte of dwFlags (0) is used to fill the entire pszDest buffer, and the buffer is null-terminated. In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any pre-existing or truncated string in the destination buffer is overwritten.
STRSAFE_NULL_ON_FAILURE
0x00000800
 If the function fails, pszDest is set to an empty string (TEXT("")). In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any pre-existing or truncated string in the destination buffer is overwritten.
STRSAFE_NO_TRUNCATION
0x00001000
 If the function fails, pszDest is untouched. Nothing is added to the original contents.

Return value

Type: HRESULT

This function can return one of the following values. It is strongly recommended that you use the SUCCEEDED and FAILED macros to test the return value of this function.

Return code Description
S_OK
 Source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.
STRSAFE_E_INVALID_PARAMETER
 The value in cbDest is larger than STRSAFE_MAX_CCH * sizeof(TCHAR), an invalid flag was passed, or there are discrepancies between the size of the pszDest, cbDest, and the amount of material to append in pszSrc.
STRSAFE_E_INSUFFICIENT_BUFFER
 The copy operation failed due to insufficient buffer space. Depending on the value of dwFlags, the destination buffer may contain a truncated, null-terminated version of the intended result. In situations where truncation is acceptable, this may not necessarily be seen as a failure condition.
 

Note that this function returns an HRESULT value, unlike the functions that it replaces.

Remarks

Compared to the functions it replaces, StringCbCatNEx provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCbCatNEx always null-terminates and never overflows a valid destination buffer, even if the contents of the source string change during the operation.

Behavior is undefined if the strings pointed to by pszSrc and pszDest overlap.

Neither pszSrc nor pszDest should be NULL unless the STRSAFE_IGNORE_NULLS flag is specified, in which case both may be NULL. However, an error due to insufficient space may still be returned even though NULL values are ignored.

StringCbCatNEx can be used in its generic form, or in its more specific forms. The data type of the string determines the form of this function that you should use.

String Data Type String Literal Function
char "string" StringCbCatNExA
TCHAR TEXT("string") StringCbCatNEx
WCHAR L"string" StringCbCatNExW
 

Note

The strsafe.h header defines StringCbCatNEx as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement Value
Minimum supported client Windows XP with SP2 [desktop apps | UWP apps]
Minimum supported server Windows Server 2003 with SP1 [desktop apps | UWP apps]
Target Platform Windows
Header strsafe.h

See also

Reference

StringCbCatEx

StringCbCatN

StringCchCatNEx