Doubts about C++ template programming are resolved one by one

C++ template programming eliminates doubts: the compiler infers template parameters through type inference rules; the constexpr keyword handles constants that depend on template parameters; template specialization provides implementation for specific parameters; recursive templates use enable_if to assist type checking. Practical cases demonstrate its functions such as factorial calculation and quick sorting.

Doubts about C++ template programming are resolved one by one

Introduction

C++ template programming is a powerful tool that allows you to generate code at compile time, thereby improving efficiency and reusability. However, it also intimidates some developers. This article aims to eliminate doubts in C++ template programming and provide practical examples.

Common doubts

1. Type inference

• Problem: Compilation How does the compiler infer template parameters?
• Answer: The compiler uses type inference rules to infer parameter types, and these rules are based on function parameters and return types.

2. Constants that depend on template parameters

• Question: What to do if template parameters can be changed Constants that depend on template parameters?
• Answer: Using the constexpr keyword, the compiler will embed the constant value into the generated code instead of calculating it at runtime.

3. Template Specialization

• Question: How to provide different implementations for specific template parameters?
• Answer: Using template specialization, you can provide completely different implementations for specific parameter types without modifying the template itself.

4. Recursive template

• Question: How to write a recursive template?
• Answer: Call itself within the template, provided that the number of recursive calls is limited. Use enable_if to help the compiler pass type checking.

Practical case

1. Calculate factorial

template<int N>
struct Factorial {
    static const int value = N * Factorial<N - 1>::value;
};

template<>
struct Factorial<0> {
    static const int value = 1;
};

int main() {
    cout << Factorial<5>::value << endl; // 输出 120
    return 0;
}

2. Sorting algorithm

template<typename T>
void quicksort(T* arr, int start, int end) {
    if (start >= end) {
        return;
    }
    int pivot = arr[end];
    int partition = start - 1;
    for (int i = start; i < end; ++i) {
        if (arr[i] < pivot) {
            swap(arr[i], arr[++partition]);
        }
    }
    swap(arr[++partition], arr[end]);
    quicksort(arr, start, partition - 1);
    quicksort(arr, partition + 1, end);
}

Conclusion

By understanding these common doubts and mastering practical cases, you can confidently use C++ template programming to unleash its powerful capabilities.

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