# std::basic_string<CharT,Traits,Allocator>::find_first_of

From cppreference.com
< cpp‎ | string‎ | basic string

| (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)
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) |
| (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)
template < class T > size_type find_first_of( const T& t, size_type pos = 0 ) const noexcept(/* see below */); | (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 `str`.
2) Finds the first character equal to one of the characters in the range `[s, s+count)`. This range can include null characters.
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)`.
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

5)
`noexcept` specification:
noexcept(std::is_nothrow_convertible_v<const T&, std::basic_string_view<CharT, Traits>>)

### 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

Run this code

    #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

### See also

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)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/string/basic_string/find_first_of&oldid=108119"