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std::strcspn(3) 	       C++ Standard Libary		 std::strcspn(3)

NAME
     std::strcspn - std::strcspn

Synopsis
	Defined in header <cstring>
	std::size_t strcspn( const char *dest, const char *src );

	Returns  the  length  of  the maximum initial segment of the byte string
     pointed to by
	dest, that consists of only the characters  not  found	in  byte  string
     pointed to by
	src.

	The function name stands for "complementary span".

Parameters
	dest - pointer to the null-terminated byte string to be analyzed
	src   -  pointer  to  the  null-terminated byte string that contains the
     characters to
	       search for

Return value
	The length of the maximum initial segment that contains only  characters
     not found in
	the byte string pointed to by src.

Example
     // Run this code

      #include <cstddef>
      #include <cstring>
      #include <iomanip>
      #include <iostream>
      #include <string>

      int main()
      {
	  std::string s = "abcde312$#@";
	  const char* invalid = "*$#";

	  const std::size_t valid_len = std::strcspn(s.c_str(), invalid);
	  if (valid_len != s.size())
	  {
	      std::cout << std::quoted(s)
			<< " contains invalid chars starting at position "
			<< valid_len << '\n'
			<< std::string(valid_len + 1, '-') << "^\n";
	  }
      }

Output:
      "abcde312$#@" contains invalid chars starting at position 8
      ---------^

See also
		      returns  the  length  of	the maximum initial segment that
     consists
	strspn	      of only the characters found in another byte string
		      (function)
		      returns the length of the  maximum  initial  segment  that
     consists
	wcscspn       of only the wide not found in another wide string
		      (function)
	strpbrk        finds  the  first location of any character from a set of
     separators
		      (function)
		      find first occurrence of characters
	find_first_of	  (public     member	  function	of	std::ba-
     sic_string<CharT,Traits,Allocator>)

	C documentation for
	strcspn

http://cppreference.com 	   2024.06.10			 std::strcspn(3)
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