RtlStringCbLengthW - 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_CB_FUNCTIONS

_Must_inspect_result_
NTSTRSAFEDDI
    RtlStringCbLengthW(
            _In_reads_or_z_(cbMax / sizeof(wchar_t)) STRSAFE_PCNZWCH psz,
            _In_ _In_range_(1, NTSTRSAFE_MAX_CCH * sizeof(wchar_t)) size_t cbMax,
            _Out_opt_ _Deref_out_range_(<, cbMax - 1) size_t* pcbLength)
{
    NTSTATUS status;
    size_t cchMax = cbMax / sizeof(wchar_t);
    size_t cchLength = 0;

    if ((psz == NULL) || (cchMax > NTSTRSAFE_MAX_CCH))
    {
        status = STATUS_INVALID_PARAMETER;
    }
    else
    {
        status = RtlStringLengthWorkerW(psz, cchMax, &cchLength);
    }

    if (pcbLength)
    {
        if (NT_SUCCESS(status))
        {
            // safe to multiply cchLength * sizeof(wchar_t) since cchLength < NTSTRSAFE_MAX_CCH and sizeof(wchar_t) is 2
            *pcbLength = cchLength * sizeof(wchar_t);
        }
        else
        {
            *pcbLength = 0;
        }
    }

    return status;
}

#endif
#endif
#endif

View code on GitHub
// ntstrsafe.h

NTSTRSAFEDDI RtlStringCbLengthW(
  [in] STRSAFE_PCNZWCH psz,
  [in] size_t          cbMax,
       size_t          *pcbLength
);
View the official Windows Driver Kit DDI reference

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

RtlStringCbLengthW function

Description

The RtlStringCbLengthW and RtlStringCbLengthA functions determine the length, in bytes, of a supplied string.

Parameters

psz [in]

A pointer to a buffer that contains a null-terminated string, the length of which will be checked.

cbMax [in]

The maximum number of bytes allowed in the buffer that is pointed to by psz, including the terminating null character.

For Unicode strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(WCHAR).

For ANSI strings, the maximum number of bytes is NTSTRSAFE_MAX_CCH * sizeof(char).

pcbLength

If the caller supplies a non-NULL address pointer, the function loads the address with the length, in bytes, of the string that is contained in the buffer. The length does not include the string's terminating null character.

Return value

The function returns one of the NTSTATUS values that are listed in the following table. For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Return code Description
STATUS_SUCCESS This success status means the string at psz was not NULL, and the length of the string (including the terminating null character) is less than or equal to cbMax characters.
STATUS_INVALID_PARAMETER This error status means the value in psz is NULL, cbMax is larger than NTSTRSAFE_MAX_CCH * sizeof(TCHAR), or psz is longer than cbMax.

Remarks

RtlStringCbLengthW and RtlStringCbLengthA should be used instead of strlen. Use these functions to ensure that a string is not larger than a given length, in bytes. If that condition is met, RtlStringCbLengthW and RtlStringCbLengthA return the current length of the string in bytes, not including those bytes used for the terminating null character.

Use RtlStringCbLengthW to handle Unicode strings and RtlStringCbLengthA to handle ANSI strings. The form you use depends on your data, as shown in the following table.

String data type String literal Function
WCHAR L"string" RtlStringCbLengthW
char "string" RtlStringCbLengthA

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

See also

RtlStringCchLength

View the official Windows Driver Kit DDI reference

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