std::pair and std::tuple

std::pair and std::tuple

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Prerequisites

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1. std::pair

std::pair is a simple container that holds exactly two values.

std::pair<T1, T2>

Useful for grouping two related values together.

• Return two values from a function
• Store simple key-value pairs
• Use in STL containers (e.g., map, priority_queue)

✔️ Declaration

#include <utility>

std::pair<int, std::string> p;

✔️ Initialization

std::pair<int, std::string> p = {1, "apple"};

Or:

auto p = std::make_pair(1, "apple");

✔️ Access

std::cout << p.first;   // 1
std::cout << p.second;  // apple

✔️ Comparison

std::pair<int, int> a = {1, 2};
std::pair<int, int> b = {1, 3};

if (a < b)
{
    // true (lexicographical comparison)
}

• Compare .first
• If equal → compare .second

2. std::tuple

std::tuple is a container that can hold multiple values (more than two).

std::tuple<T1, T2, T3, ...>

• Return multiple values from a function
• Temporary grouping of heterogeneous data
• Avoid creating a struct for simple cases

✔️ Declaration

#include <tuple>

std::tuple<int, std::string, double> t;

✔️ Initialization

auto t = std::make_tuple(1, "apple", 3.14);

✔️ Access

std::cout << std::get<0>(t);  // 1
std::cout << std::get<1>(t);  // apple
std::cout << std::get<2>(t);  // 3.14

✔️ Structured Binding (C++17)

auto [id, name, value] = t;

std::cout << id << " " << name << " " << value;

Much cleaner and readable

✔️ Modify Value

std::get<0>(t) = 10;

✔️ Comparison

std::tuple<int, int, int> a = {1, 2, 3};
std::tuple<int, int, int> b = {1, 2, 4};

if (a < b)
{
    // true
}

Also lexicographical comparison

3. std::pair vs std::tuple

Feature	pair	tuple
Number of elements	2	2 or more
Access	.first, .second	std::get<N>
Readability	High	Lower (index-based)
Flexibility	Low	High

// pair
std::pair<int, int> p = {1, 2};

// tuple
std::tuple<int, int, int> t = {1, 2, 3};

4. Common Mistakes

❌ Forgetting index type

std::get<i>(t);  // ❌ wrong

✔️ Must be compile-time constant:

std::get<0>(t);

❌ Overusing tuple

If structure becomes complex:

std::tuple<int, std::string, double, int, float>

Better to use:

struct Data
{
    int id;
    std::string name;
    double value;
};