clang-tidy - readability-string-compare — Extra Clang Tools 21.1.8 documentation

# Extra Clang Tools 21.1.8 documentation

## clang-tidy - readability-string-compare

# readability-string-compare

Finds string comparisons using the compare method.

A common mistake is to use the string’s `compare` method instead of using the equality or inequality operators. The compare method is intended for sorting functions and thus returns a negative number, a positive number or zero depending on the lexicographical relationship between the strings compared. If an equality or inequality check can suffice, that is recommended. This is recommended to avoid the risk of incorrect interpretation of the return value and to simplify the code. The string equality and inequality operators can also be faster than the `compare` method due to early termination.

## Example

    // The same rules apply to std::string_view.
    std::string str1{"a"};
    std::string str2{"b"};

    // use str1 != str2 instead.
    if (str1.compare(str2)) {
    }

    // use str1 == str2 instead.
    if (!str1.compare(str2)) {
    }

    // use str1 == str2 instead.
    if (str1.compare(str2) == 0) {
    }

    // use str1 != str2 instead.
    if (str1.compare(str2) != 0) {
    }

    // use str1 == str2 instead.
    if (0 == str1.compare(str2)) {
    }

    // use str1 != str2 instead.
    if (0 != str1.compare(str2)) {
    }

    // Use str1 == "foo" instead.
    if (str1.compare("foo") == 0) {
    }

The above code examples show the list of if-statements that this check will give a warning for. All of them use `compare` to check equality or inequality of two strings instead of using the correct operators.

## Options

StringLikeClasses

  A string containing semicolon-separated names of string-like classes. By default contains only `::std::basic_string` and `::std::basic_string_view`. If a class from this list has a `compare` method similar to that of `std::string`, it will be checked in the same way.

### Example

    struct CustomString {
    public:
      int compare (const CustomString& other) const;
    }

    CustomString str1;
    CustomString str2;

    // use str1 != str2 instead.
    if (str1.compare(str2)) {
    }

If StringLikeClasses contains `CustomString`, the check will suggest replacing `compare` with equality operator.