Comparing string* in C++ - c++

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:
a==b.
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;
}