C++ Templates Cheat Sheet

Covers C++ function and class templates, template specialization, variadic templates, and concepts for writing generic, type-safe code.

3 PagesAdvancedApr 15, 2026

Function Templates

Write one function that works across multiple types.

cpp

template <typename T>T myMax(T a, T b) {    return (a > b) ? a : b;}int i = myMax(3, 7);            // T deduced as intdouble d = myMax(1.5, 2.5);     // T deduced as doublestd::string s = myMax<std::string>("abc", "abd");  // explicit instantiation

Class Templates

Parameterize an entire class by type.

cpp

template <typename T>class Stack {public:    void push(const T& value) { data.push_back(value); }    void pop() { data.pop_back(); }    T& top() { return data.back(); }    bool empty() const { return data.empty(); }private:    std::vector<T> data;};Stack<int> intStack;intStack.push(42);// Non-type template parametertemplate <typename T, size_t N>class FixedArray {    T data[N];};FixedArray<int, 10> arr;

Template Specialization

Provide a custom implementation for a specific type.

cpp

template <typename T>struct TypeName {    static std::string get() { return "unknown"; }};// Full specializationtemplate <>struct TypeName<int> {    static std::string get() { return "int"; }};// Partial specialization (only allowed for class/struct templates)template <typename T>struct TypeName<T*> {    static std::string get() { return TypeName<T>::get() + "*"; }};

Variadic Templates

Accept an arbitrary number of template arguments.

cpp

template <typename T>T sum(T v) { return v; }template <typename T, typename... Args>T sum(T first, Args... rest) {    return first + sum(rest...);       // recursive parameter pack expansion}sum(1, 2, 3, 4);   // 10// C++17 fold expression, no recursion neededtemplate <typename... Args>auto sumFold(Args... args) {    return (args + ...);}

Key Concepts

Terminology for reasoning about templates.

Template Instantiation- The compiler generates concrete code for each distinct set of template arguments used.
SFINAE- "Substitution Failure Is Not An Error" - invalid substitutions remove an overload from consideration instead of erroring.
Concepts (C++20)- Named compile-time predicates that constrain template parameters, e.g. template<std::integral T>.
Type Trait- A compile-time metafunction like std::is_integral<T> or std::enable_if, from <type_traits>.
Two-Phase Lookup- Template code is checked at definition (non-dependent names) and again at instantiation (dependent names).

Pro Tip

Use C++20 concepts (e.g. template<std::integral T>) instead of std::enable_if SFINAE tricks when available - they give far clearer compiler errors and self-documenting constraints.

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