std::basic_string<CharT,Traits,Allocator>::compare

Compares two character sequences.

# Declarations

int compare( const basic_string& str ) const;

(noexcept since C++11) (constexpr since C++20)

int compare( size_type pos1, size_type count1,
const basic_string& str ) const;

(constexpr since C++20)

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) (constexpr since C++20)

int compare( const CharT* s ) const;

(constexpr since C++20)

int compare( size_type pos1, size_type count1,
const CharT* s ) const;

(constexpr since C++20)

int compare( size_type pos1, size_type count1,
const CharT* s, size_type count2 ) const;

(constexpr since C++20)

template< class StringViewLike >
int compare( const StringViewLike& t ) const noexcept(/* see below */);

(since C++17) (constexpr since C++20)

template< class StringViewLike >
int compare( size_type pos1, size_type count1,
const StringViewLike& t ) const;

(since C++17) (constexpr since C++20)

template< class StringViewLike >
int compare( size_type pos1, size_type count1,
const StringViewLike& t,
size_type pos2, size_type count2 = npos) const;

(since C++17) (constexpr since C++20)

# 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
t: object (convertible to std::basic_string_view) to compare to

# 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

#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);
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 5	C++98	the parameter count2 of overload (6)had a default argument npos	default argument removed,split to overloads (5) and (6)
LWG 847	C++98	there was no exception safety guarantee	added strong exception safety guarantee
LWG 2946	C++17	overload (7) caused ambiguity in some cases	avoided by making it a template
P1148R0	C++17	noexcept for overload (7) was accidentallydropped by the resolution of LWG2946	restored

std::basic_string<CharT,Traits,Allocator>::compare

# Declarations

# Parameters

# Notes

# Example

# Defect reports

# See also