StringCbCopyNEx
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8/27/2008
This function is a replacement for strncpy.
StringCbCopyNEx copies a given number of bytes from a source string.
The size, in bytes, of the destination buffer is provided to the function to ensure that StringCbCopyNEx does not write past the end of this buffer.
StringCbCopyNEx adds to the functionality of StringCbCopyN by returning a pointer to the end of the destination string, and by returning the number of bytes left unused in that string.
Flags can be passed to the function for additional control.
Syntax
HRESULT StringCbCopyNEx(
LPTSTR pszDest,
size_t cbDest,
LPCTSTR pszSrc,
size_t cbSrc,
LPTSTR *ppszDestEnd,
size_t *pcbRemaining,
DWORD dwFlags
);
Parameters
- pszDest
[out] Pointer to a buffer that receives the copied string.
cbDest
[in] Size of pszDest, in bytes.This value must be at least large enough to hold the copied bytes (the length of pszSrc or the value of cbSrc, whichever is smaller) as well as to account for the terminating null character.
The maximum number of bytes allowed is STRSAFE_MAX_CCH * sizeof(TCHAR).
pszSrc
[in] Pointer to a buffer containing the source string.This source string must be null-terminated.
- cbSrc
[in] The maximum number of bytes to copy from pszSrc to pszDest.
p pszDestEnd
[out] Address of a pointer to the end of pszDest.If ppszDestEnd is non-NULL and data is copied into the destination buffer, this points to the terminating null character at the end of the string.
pcbRemaining
[out] Pointer to a variable that indicates 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.
dwFlags
[in] One or more of the following values.Value Description STRSAFE_FILL_BEHIND_NULL
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
Treat null string pointers like empty strings (TEXT("")).
STRSAFE_FILL_ON_FAILURE
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 truncated string returned is overwritten.
STRSAFE_NULL_ON_FAILURE
If the function fails, pszDest is set to an empty string (TEXT("")).
In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any truncated string is overwritten.
STRSAFE_NO_TRUNCATION
As in the case of STRSAFE_NULL_ON_FAILURE, if the function fails, pszDest is set to an empty string (TEXT("")).
In the case of a STRSAFE_E_INSUFFICIENT_BUFFER failure, any truncated string is overwritten.
Return Value
This function returns an HRESULT, as opposed to strncpy, which returns a pointer.
It is strongly recommended that you use the SUCCEEDED and FAILED macros to test the return value of this function.
| Value | Description |
|---|---|
S_OK |
Source data was present, fully copied without truncation, and the resultant destination buffer is null-terminated. |
STRSAFE_E_INVALID_PARAMETER |
Either pszDest or pszSrc is greater than STRSAFE_MAX_CCH * sizeof(TCHAR), pszDest is NULL when there is source data present to copy, or an invalid flag was passed. |
STRSAFE_E_INSUFFICIENT_BUFFER |
The copy operation failed due to insufficient buffer space. Depending on the value of dwFlags, the destination buffer might contain a truncated, null-terminated version of the intended result. Where truncation is acceptable, this is not necessarily a failure condition. |
Remarks
StringCbCopyNEx provides additional processing for proper buffer handling in your code.
Poor buffer handling is implicated in many security issues that involve buffer overruns. StringCbCopyNEx always null-terminates a nonzero-length destination buffer.
StringCbCopyNEx can be used in its generic form, or specifically as StringCbCopyNExA (for ANSI strings) or StringCbCopyNExW (for Unicode strings). The form to use is determined by your data.
| String data type | String literal | Function |
|---|---|---|
char |
"string" |
StringCbCopyNExA |
TCHAR |
TEXT("string") |
StringCbCopyNEx |
WCHAR |
L"string" |
StringCbCopyNExW |
Although this routine is meant as a replacement for strncpy, there are differences in behavior. If cbSrc is larger than the number of bytes in pszSrc, StringCbCopyNEx, unlike strncpy, does not continue to pad pszDest with null characters until cbSrc bytes have been copied.
If the strings pointed to by pszSrc and pszDest overlap, behavior is undefined.
Neither pszSrc nor pszDest should be NULL unless the STRSAFE_IGNORE_NULLS flag is specified; in which case both might be NULL. However, an error due to insufficient space might still be returned even though null values are ignored.
Requirements
| Header | strsafe.h |
| Windows Embedded CE | Windows CE 5.0 and later |