NAME¶

std::basic_string::find_first_of - std::basic_string::find_first_of

Synopsis¶

size_type find_first_of( const (until
basic_string& str, size_type pos = 0 C++11)
) const;
size_type find_first_of( const (since
basic_string& str, C++11)
size_type pos = 0 ) const noexcept; (until
C++20)
constexpr size_type find_first_of( (since
const basic_string& str, C++20)
size_type pos = 0 ) const noexcept;
size_type find_first_of( const (until
CharT* s, size_type pos, size_type C++20)
count ) const;
constexpr size_type find_first_of(
const CharT* s, (since
size_type pos, size_type count ) C++20)
const;
size_type find_first_of( const (until
CharT* s, size_type pos = 0 ) const; C++20)
constexpr size_type find_first_of( (since
const CharT* s, size_type pos = 0 ) C++20)
const;
size_type find_first_of( CharT ch, (until
size_type pos = 0 ) const; (1) C++11)
(since
size_type find_first_of( CharT ch, C++11)
size_type pos = 0 ) const noexcept; (until
C++20)
constexpr size_type find_first_of( (2) (since
CharT ch, size_type pos = 0 ) const C++20)
noexcept;
template < class StringViewLike > (3)

size_type (since
find_first_of( const StringViewLike& (4) C++17)
t, (until
C++20)
size_type pos = 0 ) const
noexcept(/* see below */); (5)
template < class StringViewLike >

constexpr size_type
find_first_of( const StringViewLike& (since
t, C++20)

size_type pos = 0 ) const
noexcept(/* see below */);

Finds the first character equal to one of the characters in the given character
sequence. The search considers only the interval [pos, size()). If the character is
not present in the interval, 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.
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).
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.

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.

Exceptions¶

5)
noexcept specification:
noexcept(std::is_nothrow_convertible_v<const T&, std::basic_string_view<CharT,
Traits>>)

Notes¶

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

Example¶

// Run this code

#include <cassert>
#include <iostream>
#include <string>
#include <string_view>

int main() {
using namespace std::string_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);
//
assert(sz == std::string::npos);

// (2)
const char* buf = "xyzabc";
sz = "consteval"s.find_first_of(buf, 0, 3);
//
assert(sz == std::string::npos);
sz = "consteval"s.find_first_of(buf, 0, 6);
// └─────────────────────────┘c in buf
assert(sz == 0);

// (3)
sz = "decltype"s.find_first_of(buf);
// └──────────────────────┘c in buf
assert(sz == 2);

// (4)
sz = "co_await"s.find_first_of('a');
// └──────────────────────┘
assert(sz == 3);

// (5)
std::string_view sv{"int"};
sz = "constinit"s.find_first_of(sv);
// └───────────────────────┘n in sv
assert(sz == 2);

std::cout << "All tests passed.\n";
}

Possible output:¶

All tests passed.

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 2064 C++11 overload (3) and (4) were noexcept removed
LWG 2946 C++17 string_view overload causes ambiguity in avoided by making it a
some cases template
P1148R0 C++11 noexcept for overload (4)/(5) was restored
C++17 accidently dropped by LWG2064/LWG2946

See also¶

find find characters in the string
(public member function)
rfind find the last occurrence of a substring
(public member function)
find_first_not_of find first absence of characters
(public member function)
find_last_of find last occurrence of characters
(public member function)
find_last_not_of find last absence of characters
(public member function)
find_first_of find first occurrence of characters
(C++17) (public member function of std::basic_string_view<CharT,Traits>)
returns the length of the maximum initial segment that consists
strspn of only the characters found in another byte string
(function)