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StringCchCatEx function

Concatenates 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.

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

StringCchCatEx is a replacement for the following functions:

Syntax


HRESULT StringCchCatEx(
  _Inout_    LPTSTR pszDest,
  _In_       size_t cchDest,
  _In_       LPCTSTR pszSrc,
  _Out_opt_  LPTSTR *ppszDestEnd,
  _Out_opt_  size_t *pcchRemaining,
  _In_       DWORD dwFlags
);

Parameters

pszDest [in, out]

Type: LPTSTR

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

cchDest [in]

Type: size_t

The size of the destination buffer, in characters. This value must equal the length of pszSrc plus the length of pszDest plus 1 to account for both strings and the terminating null character. The maximum number of characters allowed is STRSAFE_MAX_CCH.

pszSrc [in]

Type: LPCTSTR

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

ppszDestEnd [out, optional]

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.

pcchRemaining [out, optional]

Type: size_t*

The number of unused characters in pszDest, including the terminating null character. If pcchRemaining is NULL, the count is not kept or returned.

dwFlags [in]

Type: DWORD

One or more of the following values.

ValueMeaning
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("")). This flag is useful for emulating functions such as lstrcpy.

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 codeDescription
S_OK

Source data was present, the strings were fully concatenated without truncation, and the resultant destination buffer is null-terminated.

STRSAFE_E_INVALID_PARAMETER

The value in cchDest is either 0 or larger than STRSAFE_MAX_CCH, or the destination buffer is already full.

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

StringCchCatEx provides additional processing for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCchCatEx 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.

StringCchCatEx 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, as shown in the following table.

String Data TypeString LiteralFunction
char"string"StringCchCatExA
TCHARTEXT("string")StringCchCatEx
WCHARL"string"StringCchCatExW

 

Requirements

Minimum supported client

Windows XP with SP2 [desktop apps | Windows Store apps]

Minimum supported server

Windows Server 2003 with SP1 [desktop apps | Windows Store apps]

Header

Strsafe.h

Unicode and ANSI names

StringCchCatExW (Unicode) and StringCchCatExA (ANSI)

See also

Reference
StringCchCat
StringCbCatEx
StringCchCatNEx

 

 

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