Say I have a Person class like this.
<code>class Person
{
friend std::ostream &operator<<(std::ostream &out, const Person &operand);
public:
Person(std::string name, std::string address, int age, int height, int weight)
: m_name(name), m_address(address), m_age(age), m_height(height), m_weight(weight)
{
}
public:
std::string m_name;
std::string m_address;
int m_age;
int m_height;
int m_weight;
};
std::ostream &operator<<(std::ostream &out, const Person &operand)
{
out << "Person [" << operand.m_name << ", " << operand.m_age << "]";
return out;
}
</code>
<code>class Person
{
friend std::ostream &operator<<(std::ostream &out, const Person &operand);
public:
Person(std::string name, std::string address, int age, int height, int weight)
: m_name(name), m_address(address), m_age(age), m_height(height), m_weight(weight)
{
}
public:
std::string m_name;
std::string m_address;
int m_age;
int m_height;
int m_weight;
};
std::ostream &operator<<(std::ostream &out, const Person &operand)
{
out << "Person [" << operand.m_name << ", " << operand.m_age << "]";
return out;
}
</code>
class Person
{
friend std::ostream &operator<<(std::ostream &out, const Person &operand);
public:
Person(std::string name, std::string address, int age, int height, int weight)
: m_name(name), m_address(address), m_age(age), m_height(height), m_weight(weight)
{
}
public:
std::string m_name;
std::string m_address;
int m_age;
int m_height;
int m_weight;
};
std::ostream &operator<<(std::ostream &out, const Person &operand)
{
out << "Person [" << operand.m_name << ", " << operand.m_age << "]";
return out;
}
Currently trying cpp 20 projections, so I can sort using projections like this.
<code>std::ranges::sort(persons, {}, &Person::m_age);
</code>
<code>std::ranges::sort(persons, {}, &Person::m_age);
</code>
std::ranges::sort(persons, {}, &Person::m_age);
Just curious, how about descending?
Tried the following, gives compiler error.
<code>std::ranges::sort(persons, {}, -1 * &Person::m_age);
</code>
<code>std::ranges::sort(persons, {}, -1 * &Person::m_age);
</code>
std::ranges::sort(persons, {}, -1 * &Person::m_age);
Also tried reverse as following. Again compiler error
<code>std::ranges::reverse(persons, {}, &Person::m_age);
</code>
<code>std::ranges::reverse(persons, {}, &Person::m_age);
</code>
std::ranges::reverse(persons, {}, &Person::m_age);
FYI used the following for compilation
<code>g++ "-static" -o main.exe .*.cpp -std=c++20
</code>
<code>g++ "-static" -o main.exe .*.cpp -std=c++20
</code>
g++ "-static" -o main.exe .*.cpp -std=c++20
1
With std::ranges::sort you can specify a comparator in addition to the projection.
The default is std::ranges::less which gives an ascending order.
To get the opposite order (descending) you can use std::ranges::greater:
<code>std::ranges::sort(persons, std::ranges::greater{}, &Person::m_age);
</code>
<code>std::ranges::sort(persons, std::ranges::greater{}, &Person::m_age);
</code>
std::ranges::sort(persons, std::ranges::greater{}, &Person::m_age);
Live demo
1