Using std::ranges::find() with Custom Data Types
How can I use std::ranges::find() with custom data types that don't implement the equality operator ==?
To use std::ranges::find() with custom data types that don't implement the equality operator ==, you need to define this operator for your custom type.
The find() algorithm relies on this operator to compare elements.
Defining the Equality Operator
Let's say you have a custom data type called MyStruct:
struct MyStruct {
int Value;
};To make MyStruct work with std::ranges::find(), you need to define the equality operator:
struct MyStruct {
int Value;
bool operator==(const MyStruct& Other) const {
return Value == Other.Value;
}
};Using std::ranges::find() with Custom Data Types
Now, you can use std::ranges::find() with a std::vector of MyStruct:
#include <algorithm>
#include <iostream>
#include <vector>
struct MyStruct {
int Value;
bool operator==(const MyStruct& Other) const {
return Value == Other.Value;
}
};
int main() {
std::vector<MyStruct> Numbers{
{1}, {2}, {3}, {4}, {5}
};
MyStruct target{3};
auto result = std::ranges::find(Numbers, target);
if (result != Numbers.end()) {
std::cout << "Found struct with value "
<< result->Value << "\n";
} else {
std::cout << "Struct not found\n";
}
}Found struct with value 3Alternative: Custom Comparison Function
If you cannot modify the custom type to include the equality operator, you can use std::ranges::find_if() with a custom comparison function:
#include <algorithm>
#include <iostream>
#include <vector>
struct MyStruct {
int Value;
};
bool compare(const MyStruct& a, int b) {
return a.Value == b;
}
int main() {
std::vector<MyStruct> Numbers{
{1}, {2}, {3}, {4}, {5}
};
auto result = std::ranges::find_if(Numbers,
[](const MyStruct& obj) {
return compare(obj, 3);
});
if (result != Numbers.end()) {
std::cout << "Found struct with value "
<< result->Value << "\n";
} else {
std::cout << "Struct not found\n";
}
}Found struct with value 3By defining the equality operator or using std::ranges::find_if() with a custom comparison function, you can effectively search custom data types that don't implement the equality operator ==.
Search Algorithms
An introduction to the 8 main searching algorithms in the C++ standard library, including find(), find_if(), find_if_not(), find_first_of(), adjacent_find(), search_n(), search(), and find_end().