From cppreference.com
size_typefind_first_of(constbasic_string&str,size_typepos=0)const; (1)(noexcept since C++11)
(constexpr since C++20)size_typefind_first_of(constCharT*s,size_typepos,size_typecount)const; (2)(constexpr since C++20)size_typefind_first_of(constCharT*s,size_typepos=0)const; (3)(constexpr since C++20)size_typefind_first_of(CharTch,size_typepos=0)const; (4)(noexcept since C++11)
(constexpr since C++20)template<classStringViewLike>size_typefind_first_of(constStringViewLike&t,size_typepos=0)constnoexcept(/* see below */); (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,
). If none of the characters in the given character sequence is present in the range,
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
, 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
, 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<constStringViewLike&,std::basic_string_view<CharT,Traits>> is true and std::is_convertible_v<constStringViewLike&,constCharT*> 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
) identifying characters to search for Return value
Position of the found character or
if no such character is found.
Exceptions
1,4) Throws nothing.
5)
specification:
noexcept(std::is_nothrow_convertible_v<constT&,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>intmain(){usingnamespacestd::literals;std::string::size_typesz;// (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. Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 there was no exception safety guarantee added strong exception safety guarantee
C++11 overloads (3,4) were noexcept removed
C++17 overload (5) caused ambiguity in some cases avoided by making it a template
C++11
C++17 noexcept for overloads (4,5) were
accidentally dropped by LWG2064/LWG2946 restored See also
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)
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)