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.

# Declarations

size_type find_first_of( const basic_string& str, size_type pos = 0 ) const;

(noexcept since C++11) (constexpr since C++20)

size_type find_first_of( const CharT* s,
size_type pos, size_type count ) const;

(constexpr since C++20)

size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

(constexpr since C++20)

size_type find_first_of( CharT ch, size_type pos = 0 ) const;

(noexcept since C++11) (constexpr since C++20)

template< class StringViewLike >
size_type
find_first_of( const StringViewLike& t,
size_type pos = 0 ) const noexcept(/* see below */);

(since C++17) (constexpr since C++20)

# Parameters

str: string identifying characters to search for
pos: position at which to begin searching
count: length of character string identifying characters to search for
s: pointer to a character string identifying characters to search for
ch: character to search for
t: object (convertible to std::basic_string_view) identifying characters to search for

# Return value

Position of the found character or npos if no such character is found.

# Notes

Traits::eq() is used to perform the comparison.

# Example

#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 (× are not targets)     ×××
    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";
}

# Defect reports

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++11C++17	noexcept for overloads (4,5) wereaccidentally dropped by LWG2064/LWG2946	restored