NAME¶

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

Synopsis¶

size_type find_first_of( const basic_string& str, (1) (noexcept since C++11)
size_type pos = 0 ) const; (constexpr since C++20)
size_type find_first_of( const CharT* s,
size_type pos, size_type count (2) (constexpr since C++20)
) const;
size_type find_first_of( const CharT* s, size_type pos = (3) (constexpr since C++20)
0 ) const;
size_type find_first_of( CharT ch, size_type pos = 0 ) (4) (noexcept since C++11)
const; (constexpr since C++20)
template< class StringViewLike >

size_type (since C++17)
find_first_of( const StringViewLike& t, (5) (constexpr since 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 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.

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¶

1,4) Throws nothing.
5)
noexcept specification:
noexcept(std::is_nothrow_convertible_v<const T&, std::basic_string_view<CharT,
Traits>>)

If an exception is thrown for any reason, this function has no effect (strong
exception safety guarantee).

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::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";
}

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 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 avoided by making it a
cases template
P1148R0 C++11 noexcept for overloads (4,5) were restored
C++17 accidentally dropped by LWG2064/LWG2946

See also¶

find finds the first occurrence of the given substring
(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 occurrence of characters
find_first_of (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)

Category:¶

* conditionally noexcept