std::string find_first_of() method

since C++20

// (1) Const version only
constexpr size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept;

// (2) Const version only
constexpr size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;

// (3) Const version only
constexpr size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

// (4) Const version only
constexpr size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;

// (5) Const version only
template < class StringViewLike >
constexpr size_type find_first_of( const StringViewLike& t, size_type pos = 0 ) const noexcept(/* see below */);

since C++17

// (1) Const version only
size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept;

// (2) Const version only
size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;

// (3) Const version only
size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

// (4) Const version only
size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;

// (5) Const version only
template < class StringViewLike >
size_type find_first_of( const StringViewLike& t, size_type pos = 0 ) const noexcept(/* see below */);

since C++11

// (1) Const version only
size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept;

// (2) Const version only
size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;

// (3) Const version only
size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

// (4) Const version only
size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;

until C++11

// (1) Const version only
size_type find_first_of( const basic_string& str, size_type pos = 0 ) const;

// (2) Const version only
size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;

// (3) Const version only
size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

// (4) Const version only
size_type find_first_of( CharT ch, size_type pos = 0 ) const;

Finds the first character equal to one of the characters in the given character sequence.
The search considers only the interval [ pos, size() ).

• (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.

  Overload Resolution

  This overload participates in overload resolution only if 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.

Parameters

• str - string identifying characters to search for
• pos - position at which to start the search
• 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 first character of the found substring or npos if no such substring is found.

Complexity

important

This section requires improvement. You can help by editing this doc page.

Exceptions

• (1-4) (none)
• (5) noexcept specification:

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

Notes

Traits::eq() is used for comparison. By default Traits is std::char_traits<CharT>.

Example

#include <cassert>
#include <iostream>
#include <string>
#include <string_view>
 
int main() {
    using namespace std::string_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);
    //
    assert(sz == std::string::npos);
 
    // (2)
    const char* buf = "xyzabc";
    sz = "consteval"s.find_first_of(buf, 0, 3);
    //
    assert(sz == std::string::npos);
    sz = "consteval"s.find_first_of(buf, 0, 6);
    //    └─────────────────────────┘c in buf
    assert(sz == 0);
 
    // (3)
    sz = "decltype"s.find_first_of(buf);
    //      └──────────────────────┘c in buf
    assert(sz == 2);
 
    // (4)
    sz = "co_await"s.find_first_of('a');
    //       └──────────────────────┘
    assert(sz == 3);
 
    // (5)
    std::string_view sv{"int"};
    sz = "constinit"s.find_first_of(sv);
    //      └───────────────────────┘n in sv
    assert(sz == 2);
 
    std::cout << "All tests passed.\n";
}

Output

All tests passed.