std::basic_string::compare

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))

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

[edit] 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

[edit] 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.

[edit] 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;
}

[edit] 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.

[edit] Example

[edit] 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)

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

Null-terminated strings
Byte strings
Multibyte strings
Wide strings
Classes
basic_string
basic_string_view (C++17)
char_traits