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# std::basic_string::compare

From cppreference.com
< cpp‎ | string‎ | basic string

int compare( const basic_string& str ) const; | (1) |
int compare( size_type pos1, size_type count1, const basic_string& str ) const; | (2) |
int compare( size_type pos1, size_type count1, const basic_string& str, size_type pos2, size_type count2 ) const; | (3) |
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, pas2+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))

### [edit] 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

### [edit] 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.

### [edit] Exceptions

1)

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

2-3) May throw the exceptions thrown by the corresponding `basic_string` constructors.
4)

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

5-6) 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& 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;
    }

### [edit] Example

| This section is incomplete Reason: no example

### [edit] See also

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

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