std::basic_string::compare

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos

Non-member functions operator+ operator==operator!=operator<operator>operator<=operator>= swap(std::basic_string) operator<<operator>> getline stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) operator""s (C++14) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string> (C++11)(C++11)(C++11)(C++11)

 

int compare( const basic_string& str ) const;	(1)
int compare( size_type pos1, size_type count1,              const basic_string& str ) const;	(2)
	(3)
int compare( size_type pos1, size_type count1,              const basic_string& str,              size_type pos2, size_type count2 ) const;			(until C++14)
int compare( size_type pos1, size_type count1,              const basic_string& str,              size_type pos2, size_type count2 = npos ) const;			(since C++14)
int compare( const CharT* s ) const;		(4)
int compare( size_type pos1, size_type count1,              const CharT* s ) const;		(5)
int compare( size_type pos1, size_type count1,              const CharT* s, size_type count2 ) const;		(6)
int compare( std::basic_string_view<CharT, Traits> sv) const;		(7)	(since C++17)
int compare( size_type pos1, size_type count1,              std::basic_string_view<CharT, Traits> sv) const;		(8)	(since C++17)
template < class T > int compare( size_type pos1, size_type count1,              const T& t,              size_type pos2, size_type count2 = npos) const;		(9)	(since C++17)

Compares two character sequences.

1) Compares this string to str. First, calculates the number of characters to compare, as if by size_type rlen = std::min(size(), str.size()). Then compares by calling Traits::compare(data(), str.data(), rlen). For standard strings this function performs character-by-character lexicographical comparison. If the result is zero (the strings are equal so far), then their sizes are compared as follows:

Condition		Result	Return value
Traits::compare(data, arg, rlen) < 0		data is less than arg	<0
Traits::compare(data, arg, rlen) == 0	size(data) < size(arg)	data is less than arg	<0
	size(data) == size(arg)	data is equal to arg	​0​
	size(data) > size(arg)	data is greater than arg	>0
Traits::compare(data, arg, rlen) > 0		data is greater than arg	>0

2) Compares a [pos1, pos1+count1) substring of this string to str as if by basic_string(*this, pos1, count1).compare(str) (until C++17)compare(pos1, count1, std::basic_string_view<CharT, Traits>(str)) (since C++17)

3) Compares a [pos1, pos1+count1) substring of this string to a substring [pos2, pos2+count2) of str as if by basic_string(*this, pos1, count1).compare(basic_string(str, pos2, count2)) (until C++17)compare(pos1, count1, std::basic_string_view<CharT, Traits>(str), pos2, count2) (since C++17)

4) Compares this string to the null-terminated character sequence beginning at the character pointed to by s, as if by compare(basic_string(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, as if by basic_string(*this, pos, count1).compare(basic_string(s))

6) Compares a [pos1, pos1+count1) substring of this string to the first count2 characters of the character array whose first character is pointed to by s, as if by basic_string(*this, pos, count1).compare(basic_string(s, count2)). (Note: the characters from s to s+count2 may include null characters))

7) Compares this string to sv, similar to (1) except for using sv.size() and sv.data() instead of str.size() and str.data()

8) Compares a [pos1, pos1+count1) substring of this string to sv, as if by std::basic_string_view<CharT, Traits>(data(), size()).substr(pos1, count1).compare(sv)

9) Converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then 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>(data(), size()).substr(pos1, count1).compare(sv.substr(pos2, count2));. 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	-	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 compare
sv	-	std::basic_string_view to compare to
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

1)

(none)	(until C++11)
noexcept specification:   noexcept	(since C++11)

2-6) May throw the exceptions thrown by the corresponding basic_string constructors.

7) noexcept specification:   noexcept

(since C++17)

Possible implementation

template<class CharT, class Traits, class Alloc> int 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.

See also

operator==operator!=operator<operator>operator<=operator>=	lexicographically compares two strings (function template)
substr	returns a substring (public member function)
collate	defines lexicographical comparison and hashing of strings (class template)
strcoll	compares two strings in accordance to the current locale (function)
lexicographical_compare	returns true if one range is lexicographically less than another (function template)