(1) | ||
size_type find_first_of( const basic_string& str, size_type pos = 0 ) const; | (until C++11) | |
size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept; | (since C++11) (until C++20) | |
constexpr size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept; | (since C++20) | |
(2) | ||
size_type find_first_of( const CharT* s, size_type pos, size_type count ) const; | (until C++20) | |
constexpr size_type find_first_of( const CharT* s, size_type pos, size_type count ) const; | (since C++20) | |
(3) | ||
size_type find_first_of( const CharT* s, size_type pos = 0 ) const; | (until C++20) | |
constexpr size_type find_first_of( const CharT* s, size_type pos = 0 ) const; | (since C++20) | |
(4) | ||
size_type find_first_of( CharT ch, size_type pos = 0 ) const; | (until C++11) | |
size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept; | (since C++11) (until C++20) | |
constexpr size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept; | (since C++20) | |
(5) | ||
template< class StringViewLike > size_type find_first_of( const StringViewLike& t, size_type pos = 0 ) const noexcept(/* see below */); | (since C++17) (until C++20) | |
template< class StringViewLike > constexpr size_type find_first_of( const StringViewLike& t, size_type pos = 0 ) const noexcept(/* see below */); | (since C++20) |
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.
str
.[
s
,
s + count
)
. This range can include null characters.s
. The length of the string is determined by the first null character using Traits::length(s)
.ch
.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
.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
.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 |
Position of the found character or npos
if no such character is found.
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).
Traits::eq()
is used to perform the comparison.
#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.
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 accidently dropped by LWG2064/LWG2946 | restored |
finds the first occurrence of the given substring (public member function) |
|
find the last occurrence of a substring (public member function) |
|
find first absence of characters (public member function) |
|
find last occurrence of characters (public member function) |
|
find last absence of characters (public member function) |
|
(C++17) | find first occurrence of characters (public member function of std::basic_string_view<CharT,Traits> ) |
returns the length of the maximum initial segment that consists of only the characters found in another byte string (function) |
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