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StringCchLength function

Applies to: desktop apps | Metro style apps

Determines whether a string exceeds the specified length, in characters.

StringCchLength is a replacement for the following functions:

strlen, wcslen, _tcslen

Syntax

Copy

HRESULT StringCchLength(
  __in   LPCTSTR psz,
  __in   size_t cchMax,
  __out  size_t *pcch
);

Parameters

psz [in]

Type: LPCTSTR

The string whose length is to be checked.

cchMax [in]

Type: size_t

The maximum number of characters allowed in psz, including the terminating null character. This value cannot exceed STRSAFE_MAX_CCH.

pcch [out]

Type: size_t*

The number of characters in psz, not including the terminating null character. This value is valid only if pcch is not NULL and the function succeeds.

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 code	Description
S_OK	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.
STRSAFE_E_INVALID_PARAMETER	The value in psz is NULL, cchMax is larger than STRSAFE_MAX_CCH, or psz is longer than cchMax.

Note that this function returns an HRESULT value, unlike the functions that it replaces.

Remarks

Compared to the functions it replaces, StringCchLength is an additional tool for proper buffer handling in your code. Poor buffer handling is implicated in many security issues that involve buffer overruns.

StringCchLength 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.

String Data Type	String Literal	Function
char	"string"	StringCchLengthA
TCHAR	TEXT("string")	StringCchLength
WCHAR	L"string"	StringCchLengthW

Requirements

Minimum supported client	Windows XP with SP2
Minimum supported server	Windows Server 2003 with SP1
Header	Strsafe.h
Unicode and ANSI names	StringCchLengthW (Unicode) and StringCchLengthA (ANSI)

I thought that this method has no restrictions in length as it uses size_t for input/output. But if found out:
#define STRSAFE_MAX_CCH 2147483647 // max buffer size, in characters, that we support (same as INT_MAX)

So is there any strlen replacement that can handle strings that are longer than INT_MAX ?

History

11/15/2010
MichaelPB

Only use this function for untrusted input, us other functions when trusted

This API exists for verifying strings passed by untrusted callers. Most situations don't require the use of this function and will be simpler if the other string lenght functions are used.