Name
	n3664, alx-0026r4 - add strchrcnt(), strchrscnt(), wcschrcnt(), wcschrscnt()

Principles
	-  Codify existing practice to address evident deficiencies.
	-  Enable secure programming

Category
	Standardize common string APIs

Author
	Alejandro Colomar <alx@kernel.org>

History
	<https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0026.git/>

	r0 (2025-06-14):
	-  Initial draft.

	r1 (2025-06-26):
	-  s/Description/Rationale/

	r2 (2025-06-29; n3618):
	-  Clarify that the null byte is also searched.

	r3 (2025-07-03):
	-  tfix
	-  Don't repeat the name of the function within the description.

	r4 (2025-07-27; n3664):
	-  Add note about DoS.

Rationale
	It is a common operation to count the number of occurrences of
	one character or a set of characters.  Several projects define
	functions for this purpose: strchrcnt() for one character, and
	strchrscnt() for a set of characters.

	Let's provide a standard API, which will avoid loops that are
	prone to off-by-one bugs.

    DoS concerns
	While one may be concerned that these APIs may promote DoS
	attacks by searching in a loop within a loop, these APIs are
	designed to be used with (short) string literals as the second
	argument.  It would only be a concern if the second argument can
	be controlled by a user, but that would be unusual.

Design choices
	-  strchrscnt() would be enough, but strchrcnt() would be more
	   efficient for the common case of searching just one
	   character.  So, let's provide both.

Proposed wording
	Based on N3550.

    7.28  String handling <string.h>
	## New section after 7.28.5 ("Search functions")

	+7.28.5+1  Count functions
	+7.28.5+1.1  The <b>strchrcnt</b> function
	+
	+Synopsis
	+1	#include <stdio.h>
	+	size_t strchrcnt(const char *s, char c);
	+
	+Description
	+2	This function counts
	+	the number of occurrences of <tt>c</tt>
	+	in the string pointed to by <tt>s</tt>.
	+	The terminating null character
	+	is considered to be part of the string.
	+
	+Returns
	+3	This function returns
	+	the number of occurrences of <tt>c</tt>
	+	in the string pointed to by <tt>s</tt>.
	+
	+7.28.5+1.2  The <b>strchrscnt</b> function
	+
	+Synopsis
	+1	#include <stdio.h>
	+	size_t strchrscnt(const char *s, const char *chrs);
	+
	+Description
	+2	This function counts
	+	the number of occurrences of characters
	+	from the string pointed to by <tt>chrs</tt>
	+	in the string pointed to by <tt>s</tt>.
	+
	+Returns
	+3	This function returns
	+	the number of occurrences of characters
	+	from the string pointed to by <tt>chrs</tt>
	+	in the string pointed to by <tt>s</tt>.

    7.33.4  General wide string utilities
	## New section after 7.33.4.6 ("Wide string search functions")

	+7.33.4.6+1  Wide string count functions
	+7.33.4.6+1.1  The <b>wcschrcnt</b> function
	+
	+Synopsis
	+1	#include <stdio.h>
	+	size_t wcschrcnt(const wchar_t *s, wchar_t c);
	+
	+Description
	+2	This function
	+	is equivalent to
	+	<b>strchrcnt</b>,
	+	except that it handles wide characters.
	+
	+7.33.4.6+1.2  The <b>wcschrscnt</b> function
	+
	+Synopsis
	+1	#include <stdio.h>
	+	size_t wcschrscnt(const wchar_t *s, const wchar_t *chrs);
	+
	+Description
	+2	This function
	+	is equivalent to
	+	<b>strchrscnt</b>,
	+	except that it handles wide characters.