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std::basic_string::find_first_of

size_type find_first_of( const basic_string& str, size_type pos = 0 ) const;	(1)
size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;	(2)
size_type find_first_of( const CharT* s, size_type pos = 0 ) const;	(3)
size_type find_first_of( CharT ch, size_type pos = 0 ) const;	(4)
template < class T > size_type find_first_of( const T& t, size_type pos = 0 ) const;	(5)	(since C++17)

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 stras if by find_first_of(std::basic_string_view<CharT, Traits>(str), pos) (since C++17)

2) Finds the first character equal to one of the characters in the first count characters of the character string pointed to by s. s can include null characters. Equivalent to find_first_of(basic_string(s, count), pos) (until C++17)find_first_of(std::basic_string_view<CharT, Traits>(s, count), pos) (since C++17)

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. Equivalent to find_first_of(basic_string(s), pos) (until C++17)find_first_of(std::basic_string_view<CharT,Traits>(s), pos) (since C++17)

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 only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, 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) (none)	(until C++11)
1,4) `noexcept` specification: `noexcept` 2,3) (none)	(since C++11) (until C++14)
1) `noexcept` specification: `noexcept` 2-4) (none)	(since C++14)
5) Throws nothing unless the initialization of `sv` throws an exception.	(since C++17)

Notes

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

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 2946	C++17	`string_view` overload causes ambiguity in some cases	avoided by making it a template

Example

#include <iostream>
#include <string>
 
int main()
{
    // the test string
    std::string str = std::string("Hello World!");
 
    // strings and chars to search for
    std::string search_str = std::string("o");
    const char* search_cstr = "Good Bye!";
 
    std::cout << str.find_first_of(search_str) << '\n';
    std::cout << str.find_first_of(search_str, 5) << '\n';
    std::cout << str.find_first_of(search_cstr) << '\n';
    std::cout << str.find_first_of(search_cstr, 0, 4) << '\n';
    // 'x' is not in "Hello World', thus it will return std::string::npos
    std::cout << str.find_first_of('x') << '\n';
}

Possible output:

4
7
1
4
18446744073709551615

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)
strspn	returns the length of the maximum initial segment that consists of only the characters found in another byte string (function)