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)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

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 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) 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)

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)

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))

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))

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

Return value

negative value if this string is less than the other character sequence, zero if the both character sequences are equal, positive value if this string is greater than the other character sequence.

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.

Possible implementation

template<class CharT, class Traits, class Alloc> int basic_string<CharT, Traits, Alloc>::compare(const std::basic_string& str) const noexcept { size_type lhs_sz = size(); size_type rhs_sz = str.size(); int result = traits_type::compare(data(), str.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; }

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)