tcslen

tcslen is a function provided by the Windows C run-time library as part of the generic-text mapping in tchar.h. It computes the length of a null-terminated string consisting of TCHAR elements, returning the number of characters before the terminating null character.

TCHAR is a character type that can represent either a single-byte char (in ANSI builds) or a wide character wchar_t (in Unicode builds). The tcslen function therefore adapts to the active character width: in ANSI builds it maps to strlen, while in Unicode builds it maps to wcslen. Depending on the header and compiler, the symbol may appear as tcslen or as _tcslen, with tcslen often acting as a portable alias to the underlying function.

The typical signature is size_t tcslen(const TCHAR* s); The function does not include the terminating null in the count and returns the length of the string in TCHAR units. It is a read-only operation and does not modify the input string.

Usage typically requires including <tchar.h> and using TCHAR-based strings, which can be declared with the _T or _TEXT macros to remain portable across ANSI and Unicode builds. For example, const TCHAR* s = _T("example"); size_t len = tcslen(s);

Notes: tcslen counts characters, not bytes, and assumes a properly null-terminated string. It is not a function for raw buffers without a terminating null, and its meaning varies with the TCHAR mapping used by the project. See also strlen, wcslen, and the tchar.h header for related generic-text utilities.