比较 C++ 中的字符串*

Question

Let a and b be given positive integers. Consider the following C++17 code:

string* first;
first = new string[a];
//some definitions

string* second;
second = new string[b];
//some definitions

By saying a string first[i] is undefined, I mean no definition is ever made to the string first[i] after the creation code given above.

I define first and second to be equal if:

1. a==b .
2. first[i] and second[i] are equivalent for every non-negative integer i<a , in the following sense: if first[i] is undefined, then so is second[i] ; if first[i] has length l (where l is a non-negative integer), then second[i] has length l and first[i][j] is the same char as second[i][j] for every non-negative integer j<l .

In short, I want the most ordinary string equality with the emphasis on comparing the contents rather than the pointers. What is the most appropriate way to do this in C++17? I tried multiple answers and none of them works.

Answer 1

I'm assuming string is std::string .

The real solution here would be to use std::vector<std::string> rather than managing your own dynamic memory:

std::vector<std::string> first;
//some definitions

std::vector<std::string> second;
//some definitions

bool equal = (first == second); // does what you want

If, for some reason, you cannot use std::vector , the C-style approach would look something like

bool are_equal(std::string* first, std::size_t first_size, std::string* second, std::size_t second_size) {
    if (first_size != second_size) return false;
    for (std::size_t idx = 0; idx != first_size; ++idx) {
        if (first[idx] != second[idx]) return false;
    }
    return true;
}

int main() {
    string* first = new string[a];
    //some definitions

    string* second = new string[b];
    //some definitions

    bool equal = are_equal(first, a, second, b);
    return 0;
}

With C++20, prefer using std::span here

bool are_equal(std::span<const std::string> first, std::span<const std::string> second) {
    if (first.size() != second.size()) return false;
    for (std::size_t idx = 0; idx != first.size(); ++idx) {
        if (first[idx] != second[idx]) return false;
    }
    return true;
}

    int main() {
    string* first = new string[a];
    //some definitions

    string* second = new string[b];
    //some definitions

    bool equal = are_equal({first, a}, {second, b});
    return 0;
}