RtlStringCchLengthA - 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_CCH_FUNCTIONS

_Must_inspect_result_
NTSTRSAFEDDI
    RtlStringCchLengthA(
            _In_reads_or_z_(cchMax) STRSAFE_PCNZCH psz,
            _In_ _In_range_(1, NTSTRSAFE_MAX_CCH) size_t cchMax,
            _Out_opt_ _Deref_out_range_(<, cchMax) _Deref_out_range_(<=, _String_length_(psz)) size_t* pcchLength)
{
    NTSTATUS status;

    if ((psz == NULL) || (cchMax > NTSTRSAFE_MAX_CCH))
    {
        status = STATUS_INVALID_PARAMETER;
    }
    else
    {
        status = RtlStringLengthWorkerA(psz, cchMax, pcchLength);
    }

    if (!NT_SUCCESS(status) && pcchLength)
    {
        *pcchLength = 0;
    }

    return status;
}

#endif
#endif
#endif

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// ntstrsafe.h

NTSTRSAFEDDI RtlStringCchLengthA(
  [in] STRSAFE_PCNZCH psz,
  [in] size_t         cchMax,
       size_t         *pcchLength
);
View the official Windows Driver Kit DDI reference

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

RtlStringCchLengthA function

Description

The RtlStringCchLengthW and RtlStringCchLengthA functions determine the length, in characters, 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.

cchMax [in]

The maximum number of characters allowed in the buffer pointed to by psz, including the terminating null character. This value cannot exceed NTSTRSAFE_MAX_CCH.

pcchLength

If the caller supplies a non-NULL address pointer, the function loads the address with the length, in characters, 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 cchMax characters.
STATUS_INVALID_PARAMETER This error status means the value in psz is NULL, cchMax is larger than NTSTRSAFE_MAX_CCH, or psz is longer than cchMax.

Remarks

RtlStringCchLengthW and RtlStringCchLengthA should be used instead of strlen. They are used to ensure that a string is not larger than a given length, in characters. If that condition is met, RtlStringCchLengthW and RtlStringCchLengthA return the current length of the string in characters, not including the terminating null character.

Use RtlStringCchLengthW to handle Unicode strings and RtlStringCchLengthA 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" RtlStringCchLengthW
char "string" RtlStringCchLengthA

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

See also

RtlStringCbLength

View the official Windows Driver Kit DDI reference

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