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size_type find_first_of(const basic_string& str, size_type pos=0)const; | (1) | (noexcept since C++11) (constexpr since C++20) |
size_type find_first_of(const CharT* s, size_type pos, size_type count)const; | (2) | (constexpr since C++20) |
size_type find_first_of(const CharT* s, size_type pos=0)const; | (3) | (constexpr since C++20) |
size_type find_first_of( CharT ch, size_type pos=0)const; | (4) | (noexcept since C++11) (constexpr since C++20) |
template<class StringViewLike> size_type | (5) | (since C++17) (constexpr 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.
[s, s+ count). This range can include null characters.[s, s+ count) is not avalid range, the behavior is undefined.[s, s+ Traits::length(s)) is not avalid range, the behavior is undefined.Contents |
| 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 tostd::basic_string_view) identifying characters to search for |
Position of the found character ornpos if no such character is found.
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(){usingnamespace 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 matchassert(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 accidentally dropped by LWG2064/LWG2946 | restored |
| finds the first occurrence of the given substring (public member function)[edit] | |
| find the last occurrence of a substring (public member function)[edit] | |
| find first absence of characters (public member function)[edit] | |
| find last occurrence of characters (public member function)[edit] | |
| find last absence of characters (public member function)[edit] | |
| find first occurrence of characters (public member function of std::basic_string_view<CharT,Traits>)[edit] | |
| returns the length of the maximum initial segment that consists of only the characters found in another byte string (function)[edit] |
