std::string_view compare() method

since C++17

// (1) Const version only
constexpr int compare( basic_string_view v ) const noexcept;

// (2) Const version only
constexpr int compare( size_type pos1, size_type count1,
                       basic_string_view v ) const;

// (3) Const version only
constexpr int compare( size_type pos1, size_type count1, basic_string_view v,
                       size_type pos2, size_type count2 ) const;

// (4) Const version only
constexpr int compare( const CharT* s ) const;

// (5) Const version only
constexpr int compare( const CharT* s ) const;
constexpr int compare( size_type pos1, size_type count1,
                       const CharT* s ) const;

// (6) Const version only
constexpr int compare( size_type pos1, size_type count1,
                       const CharT* s, size_type count2 ) const;

Compares two character sequences.

• (1) The length rlen of the sequences to compare is std::min(size(), v.size()).
  The function compares the two views by calling Traits::compare(data(), v.data(), rlen), and returns a value according to the following table:

  important

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

• (2) Equivalent to substr(pos1, count1).compare(v).

• (3) Equivalent to substr(pos1, count1).compare(v.substr(pos2, count2)).

• (4) Equivalent to compare(basic_string_view(s)).

• (5) Equivalent to substr(pos1, count1).compare(basic_string_view(s)).

• (6) Equivalent to substr(pos1, count1).compare(basic_string_view(s, count2)).

Parameters

• v - view to compare
• s - pointer to the character string to compare to
• count1 - number of characters of this view to compare
• pos1 - position of the first character in this view to compare
• count2 - number of characters of the given view to compare
• pos2 - position of the first character of the given view to compare

Returns value

• Negative value if *this appears before the character sequence specified by the arguments, in lexicographical order.
• Zero if both character sequences compare equivalent.
• Positive value if *this appears after the character sequence specified by the arguments, in lexicographical order.

Complexity

important

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

Exceptions

(none)

Possible implementation

template<class CharT, class Traits, class Alloc>
int basic_string_view<CharT, Traits, Alloc>::compare(std::basic_string_view s) const noexcept
{
    size_type lhs_sz = size();
    size_type rhs_sz = s.size();
    int result = traits_type::compare(data(), s.data(), std::min(lhs_sz, rhs_sz));
    if (result != 0)
        return result;
    if (lhs_sz < rhs_sz)
        return -1;
    if (lhs_sz > rhs_sz)
        return 1;
    return 0;
}

Example

Main.cpp

#include <string_view>
int main() {
    using std::operator""sv;
    static_assert( "abc"sv.compare("abcd"sv) < 0 );
    static_assert( "abcd"sv.compare("abc"sv) > 0 );
    static_assert( "abc"sv.compare("abc"sv) == 0 );
    static_assert( ""sv.compare(""sv) == 0 );
}