std::basic_string<CharT,Traits,Allocator>::find_first_of

Finds the first character equal to one of the characters in the given character sequence. The search considers only the range [pos, size() ). If none of the characters in the given character sequence is present in the range, npos will be returned.

1) Finds the first character equal to one of the characters in str.

2) Finds the first character equal to one of the characters in the range [s, s + count). This range can include null characters.

If [s, s + count) is not a valid range, the behavior is undefined.

3) Finds the first character equal to one of the characters in character string pointed to by s. The length of the string is determined by the first null character using Traits::length(s).

If [s, s + Traits::length(s)) is not a valid range, the behavior is undefined.

4) Finds the first character equal to ch.

5) Implicitly converts t to a string view sv as if by std::basic_string_view <CharT, Traits> sv = t;, then finds the first character equal to one of the characters in sv.

This overload participates in overload resolution only if std::is_convertible_v <const StringViewLike&,
std::basic_string_view <CharT, Traits>> is true and std::is_convertible_v <const StringViewLike&, const CharT*> is false.

#include <cassert>
#include <iostream>
#include <string>
#include <string_view>
 
int main()
{
 using namespace std::literals;
 std::string::size_type sz;
 
 // (1)
 sz = "alignas"s.find_first_of("klmn"s);
 // └────────────────────────┘
 assert (sz == 1);
 
 sz = "alignof"s.find_first_of("wxyz"s);
 // no match
 assert (sz == std::string::npos );
 
 // (2)
 sz = "consteval"s.find_first_of("xyzabc", 0, 3);
 // no match (×ばつ are not targets) ×ばつ
 assert (sz == std::string::npos );
 
 sz = "consteval"s.find_first_of("xyzabc", 0, 6);
 // └───────────────────────────────┘
 assert (sz == 0);
 
 // (3)
 sz = "decltype"s.find_first_of("xyzabc");
 // └────────────────────────────┘
 assert (sz == 2);
 
 // (4)
 sz = "co_await"s.find_first_of('a');
 // └──────────────────────┘
 assert (sz == 3);
 
 // (5)
 sz = "constinit"s.find_first_of("int"sv);
 // └─────────────────────────┘
 assert (sz == 2);
 
 std::cout << "All tests passed.\n";
}

Output:

All tests passed.

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 847	C++98	there was no exception safety guarantee	added strong exception safety guarantee
LWG 2064	C++11	overloads (3,4) were noexcept	removed
LWG 2946	C++17	overload (5) caused ambiguity in some cases	avoided by making it a template
P1148R0	C++11 C++17	noexcept for overloads (4,5) were accidentally dropped by LWG2064/LWG2946	restored