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std::basic_string::compare(3) C++ Standard Libarystd::basic_string::compare(3) NAME std::basic_string::compare - std::basic_string::compare Synopsis (noexcept since int compare( const basic_string& str ) const; (1) C++11) (constexpr since C++20) int compare( size_type pos1, size_type count1, (2) (constexpr since const basic_string& str ) const; C++20) int compare( size_type pos1, size_type count1, const basic_string& str, (until C++14) size_type pos2, size_type count2 ) const; int compare( size_type pos1, size_type count1, (since C++14) const basic_string& str, (constexpr since C++20) size_type pos2, size_type count2 = npos ) const; int compare( const CharT* s ) const; (4) (constexpr since C++20) int compare( size_type pos1, size_type count1, (5) (constexpr since const CharT* s ) const; C++20) int compare( size_type pos1, size_type count1, (3) (constexpr since const CharT* s, size_type count2 (6) C++20) ) const; template< class StringViewLike > (since C++17) int compare( const StringViewLike& t ) const (7) (constexpr since noexcept(/* see below */); C++20) template< class StringViewLike > (since C++17) int compare( size_type pos1, size_type count1, (8) (constexpr since C++20) const StringViewLike& t ) const; template< class StringViewLike > int compare( size_type pos1, size_type count1, (since C++17) const StringViewLike& t, (9) (constexpr since C++20) size_type pos2, size_type count2 = npos) const; Compares two character sequences. 1) Compares this string to str. 2) Compares a [pos1, pos1 + count1) substring of this string to str. * If count1 > size() - pos1, the substring is [pos1, size()). 3) Compares a [pos1, pos1 + count1) substring of this string to a substring [pos2, pos2 + count2) of str. * If count1 > size() - pos1, the first substring is [pos1, size()). * If count2 > str.size() - pos2, the second substring is [pos2, str.size()). 4) Compares this string to the null-terminated character sequence beginning at the character pointed to by s with length Traits::length(s). 5) Compares a [pos1, pos1 + count1) substring of this string to the null-terminated character sequence beginning at the character pointed to by s with length Traits::length(s). * If count1 > size() - pos1, the substring is [pos1, size()). 6) Compares a [pos1, pos1 + count1) substring of this string to the characters in the range [s, s + count2). The characters in [s, s + count2) may in- clude null characters. * If count1 > size() - pos1, the substring is [pos1, size()). 7-9) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then 7) compares this string to sv; 8) compares a [pos1, pos1 + count1) substring of this string to sv, as if by std::basic_string_view<CharT, Traits>(*this).substr(pos1, count1).compare(sv); 9) compares a [pos1, pos1 + count1) substring of this string to a substring [pos2, pos2 + count2) of sv, as if by std::basic_string_view<CharT, Traits>(*this) .substr(pos1, count1).compare(sv.substr(pos2, count2)). These overloads participate 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.. A character sequence consisting of count1 characters starting at data1 is compared to a character sequence consisting of count2 characters starting at data2 as follows: * First, calculate the number of characters to compare, as if by size_type rlen = std::min(count1, count2). * Then compare the sequences by calling Traits::compare(data1, data2, rlen). For standard strings this function performs character-by-character lexicographical comparison. If the result is zero (the character sequences are equal so far), then their sizes are compared as follows: Condition Result Return value Traits::compare(data1, data2, rlen) < 0 data1 is less than <0 data2 size1 < size2 data1 is less than <0 data2 Traits::compare(data1, data2, rlen) == size1 == data1 is equal to 0 0 size2 data2 size1 > size2 data1 is greater >0 than data2 Traits::compare(data1, data2, rlen) > 0 data1 is greater >0 than data2 Parameters str - other string to compare to s - pointer to the character string to compare to count1 - number of characters of this string to compare pos1 - position of the first character in this string to compare count2 - number of characters of the given string to compare pos2 - position of the first character of the given string to com- pare t - object (convertible to std::basic_string_view) to compare to Return 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. Exceptions The overloads taking parameters named pos1 or pos2 throws std::out_of_range if the argument is out of range. 7) noexcept specification: noexcept(std::is_nothrow_convertible_v<const T&, std::ba- sic_string_view<CharT, Traits>>) 8,9) Throws anything thrown by the conversion to std::ba- sic_string_view. If an exception is thrown for any reason, this function has no ef- fect (strong exception safety guarantee). Possible implementation overload (1) template<class CharT, class Traits, class Alloc> int std::basic_string<CharT, Traits, Alloc>::compare (const std::basic_string& 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; } Notes For the situations when three-way comparison is not required, std::basic_string provides the usual relational operators (<, <=, ==, >, etc). By default (with the default std::char_traits), this function is not locale-sensitive. See std::collate::compare for locale-aware three- way string comparison. Example // Run this code #include <cassert> #include <iomanip> #include <iostream> #include <string> #include <string_view> void print_compare_result(std::string_view str1, std::string_view str2, int compare_result) { if (compare_result < 0) std::cout << std::quoted(str1) << " comes before " << std::quoted(str2) << ".\n"; else if (compare_result > 0) std::cout << std::quoted(str2) << " comes before " << std::quoted(str1) << ".\n"; else std::cout << std::quoted(str1) << " and " << std::quoted(str2) << " are the same.\n"; } int main() { std::string batman{"Batman"}; std::string superman{"Superman"}; int compare_result{0}; // 1) Compare with other string compare_result = batman.compare(superman); std::cout << "1) "; print_compare_result("Batman", "Superman", compare_result); // 2) Compare substring with other string compare_result = batman.compare(3, 3, superman); std::cout << "2) "; print_compare_result("man", "Superman", compare_result); // 3) Compare substring with other substring compare_result = batman.compare(3, 3, superman, 5, 3); std::cout << "3) "; print_compare_result("man", "man", compare_result); // Compare substring with other substring // defaulting to end of other string assert(compare_result == batman.compare(3, 3, superman, 5)); // 4) Compare with char pointer compare_result = batman.compare("Superman"); std::cout << "4) "; print_compare_result("Batman", "Superman", compare_result); // 5) Compare substring with char pointer compare_result = batman.compare(3, 3, "Superman"); std::cout << "5) "; print_compare_result("man", "Superman", compare_result); // 6) Compare substring with char pointer substring compare_result = batman.compare(0, 3, "Superman", 5); std::cout << "6) "; print_compare_result("Bat", "Super", compare_result); } Output: 1) "Batman" comes before "Superman". 2) "Superman" comes before "man". 3) "man" and "man" are the same. 4) "Batman" comes before "Superman". 5) "Superman" comes before "man". 6) "Bat" comes before "Super". Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior the parameter count2 of overload default argu- ment removed, LWG 5 C++98 (6) split to overloads (5) and had a default argument npos (6) LWG 847 C++98 there was no exception safety added strong exception safety guarantee guarantee LWG 2946 C++17 overload (7) caused ambiguity in avoided by making it a some cases template noexcept for overload (7) was P1148R0 C++17 accidentally restored dropped by the resolution of LWG2946 See also operator== operator!= operator< operator> operator<= operator>= lexicographically compares two strings operator<=> (function template) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (removed in C++20) (C++20) substr returns a substring (public member function) collate defines lexicographical comparison and hash- ing of strings (class template) strcoll compares two strings in accordance to the current locale (function) returns true if one range is lexicographi- cally less than lexicographical_compare another (function template) compares two views compare (public member function of std::basic_string_view<CharT,Traits>) Category: * conditionally noexcept http://cppreference.com 2024.06.10 std::basic_string::compare(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Possible implementation | Notes | Example | Output: | See also | Category:
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