std::basic_string<CharT,Traits,Allocator>::compare - cppreference.com (original) (raw)

Compares two character sequences.

1. Compares this string to str.

2. Compares a [pos1, pos1 + count1) substring of this string to str.

• If count1 > size() - pos1, the substring is [pos1, size()).

1. Compares a [pos1, pos1 + count1) substring of this string to a substring [pos2, pos2 + count2) of str.

• If count1 > size() - pos1, the first substring is [pos1, size()).
• If count2 > str.size() - pos2, the second substring is [pos2, str.size()).

1. Compares this string to the null-terminated character sequence beginning at the character pointed to by s with length Traits::length(s).

2. Compares a [pos1, pos1 + count1) substring of this string to the null-terminated character sequence beginning at the character pointed to by s with length Traits::length(s).

• If count1 > size() - pos1, the substring is [pos1, size()).

1. Compares a [pos1, pos1 + count1) substring of this string to the characters in the range [s, s + count2). The characters in [s, s + count2) may include null characters.

• If count1 > size() - pos1, the substring is [pos1, size()).

7-9) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then

1. compares this string to sv;

2. compares a [pos1, pos1 + count1) substring of this string to sv, as if by std::basic_string_view<CharT, Traits>(*this).substr(pos1, count1).compare(sv);

3. 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>(*this)
   .substr(pos1, count1).compare(sv.substr(pos2, count2)).

A character sequence consisting of count1 characters starting at data1 is compared to a character sequence consisting of count2 characters starting at data2 as follows:

• First, calculate the number of characters to compare, as if by size_type rlen = std::min(count1, count2).
• Then compare the sequences by calling Traits::compare(data1, data2, rlen). For standard strings this function performs character-by-character lexicographical comparison. If the result is zero (the character sequences are equal so far), then their sizes are compared as follows:

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Possible implementation
• 5 Notes
• 6 Example
• 7 Defect reports
• 8 See also

[edit] Parameters

[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

The overloads taking parameters named pos1 or pos2 throws std::out_of_range if the argument is out of range.

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

[edit] Possible implementation

[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

#include #include #include #include #include   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); }

Output:

1. "Batman" comes before "Superman".
2. "Superman" comes before "man".
3. "man" and "man" are the same.
4. "Batman" comes before "Superman".
5. "Superman" comes before "man".
6. "Bat" comes before "Super".

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also