RtlUnicodeStringCopy - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers 
#ifndef _NTSTRSAFE_H_INCLUDED_
#ifndef NTSTRSAFE_LIB_IMPL
#ifndef NTSTRSAFE_NO_UNICODE_STRING_FUNCTIONS

/*++

  NTSTATUS
  RtlUnicodeStringCopy(
  _Inout_ PUNICODE_STRING    DestinationString,
  _In_ PCUNICODE_STRING    SourceString
  );

  Routine Description:

  This routine is a safer version of the C built-in function 'strcpy' for
  UNICODE_STRINGs.

  This function returns an NTSTATUS value, and not a pointer.  It returns
  STATUS_SUCCESS if the string was copied without truncation, otherwise it
  will return a failure code. In failure cases as much of SourceString
  will be copied to Dest as possible.

Arguments:

DestinationString   - pointer to the counted unicode destination string

SourceString        -  pointer to the counted unicode source string

Notes:
Behavior is undefined if source and destination strings overlap.

DestinationString and SourceString should not be NULL.  See RtlUnicodeStringCopyEx
if you require the handling of NULL values.

Return Value:

STATUS_SUCCESS -   if there was source data and it was all copied

failure        -   the operation did not succeed

STATUS_BUFFER_OVERFLOW
Note: This status has the severity class Warning - IRPs completed with this
status do have their data copied back to user mode
-   this return value is an indication that the copy
operation failed due to insufficient space. When this
error occurs, the destination buffer is modified to
contain a truncated version of the ideal result. This is
useful for situations where truncation is ok

It is strongly recommended to use the NT_SUCCESS() macro to test the
return value of this function.

--*/

NTSTRSAFEDDI
RtlUnicodeStringCopy(
        _Inout_ PUNICODE_STRING DestinationString,
        _In_ PCUNICODE_STRING SourceString)
{
    NTSTATUS status;
    wchar_t* pszDest;
    size_t cchDest;

    status = RtlUnicodeStringValidateDestWorker(DestinationString,
            &pszDest,
            &cchDest,
            NULL,
            NTSTRSAFE_UNICODE_STRING_MAX_CCH,
            0);

    if (NT_SUCCESS(status))
    {
        wchar_t* pszSrc;
        size_t cchSrcLength;
        size_t cchNewDestLength = 0;

        status = RtlUnicodeStringValidateSrcWorker(SourceString,
                &pszSrc,
                &cchSrcLength,
                NTSTRSAFE_UNICODE_STRING_MAX_CCH,
                0);

        if (NT_SUCCESS(status))
        {
            status = RtlWideCharArrayCopyWorker(pszDest,
                    cchDest,
                    &cchNewDestLength,
                    pszSrc,
                    cchSrcLength);
        }

        // safe to multiply cchNewDestLength * sizeof(wchar_t) since cchDest < NTSTRSAFE_UNICODE_STRING_MAX_CCH and sizeof(wchar_t) is 2
        DestinationString->Length = (USHORT)(cchNewDestLength * sizeof(wchar_t));
    }

    return status;
}

#endif
#endif
#endif

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// ntstrsafe.h

NTSTRSAFEDDI RtlUnicodeStringCopy(
  [out] PUNICODE_STRING  DestinationString,
  [in]  PCUNICODE_STRING SourceString
);
View the official Windows Driver Kit DDI reference

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Windows Driver Kit DDI reference (nf-ntstrsafe-rtlunicodestringcopy)

RtlUnicodeStringCopy function

Description

The RtlUnicodeStringCopy function copies a string from one UNICODE_STRING structure to another.

Parameters

DestinationString [out]

A pointer to a UNICODE_STRING structure. The source string is copied to the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR).

SourceString [in]

A pointer to a UNICODE_STRING structure. This structure includes a buffer that contains the source string. This string will be copied to the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR).

Return value

RtlUnicodeStringCopy returns one of the following NTSTATUS values.

Return code Description
STATUS_SUCCESS This success status means that source data was present, the string was copied without truncation, and the resultant destination buffer is null-terminated.
STATUS_BUFFER_OVERFLOW This warning status means that the copy operation did not complete because of insufficient buffer space. The destination buffer contains a truncated version of the source string.
STATUS_INVALID_PARAMETER This error status means that the function received an invalid input parameter. For more information, see the following list.

RtlUnicodeStringCopy returns the STATUS_INVALID_PARAMETER value when one of the following occurs:

For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Remarks

The RtlUnicodeStringCopy function uses the destination buffer's size to ensure that the copy operation does not write past the end of the buffer. If the string must be truncated at the end of the destination buffer, the function does not terminate the resultant string with a null character.

If the source and destination strings overlap, the behavior of the function is undefined.

The SourceString and DestinationString pointers cannot be NULL. If you need to handle NULL pointer values, use the RtlUnicodeStringCopyEx function.

For more information about the safe string functions, see Using Safe String Functions.

See also

RtlUnicodeStringCopyEx

UNICODE_STRING

View the official Windows Driver Kit DDI reference

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