C++ range-based for statement

range-based-for.cpp

#include <iostream>

class Range {
    int start, end_;
    int step;
public:
    Range(int end) : start(0), end_(end), step(1) { }
    Range(int b, int e, int s) : start(b), end_(e), step(s) { }

    class Iterator {
        int cur;
        int step;
    public:
        Iterator(int c, int s) : cur(c), step(s) { }

        // API for range-based for statement
        bool operator !=(const Iterator& rhs) const { return cur != rhs.cur; }
        Iterator& operator ++() { cur += step; return *this; }
        int       operator *()  { return cur; }
    };

    Iterator begin() const { return Iterator(start, step); }
    Iterator end()   const { return Iterator(end_, 0); }

    Range reverse()  const { return Range(end_ - step, start - step, 0 - step); }
};

int main() {
#define PRINT_RANGE(R)                                  \
    std::cout << #R " = ";                              \
    for (auto i: R) std::cout << i << " ";              \
    std::cout << std::endl;

    PRINT_RANGE(Range(5));
    PRINT_RANGE(Range(2, 10, 2));
    PRINT_RANGE(Range(10, 0, -2));
    PRINT_RANGE(Range(5).reverse());
}

// g++ -O2 range-based-for.cpp && ./a.out

SimpleCppRange.md

C++ Simple Range

A simple Range class for int with c++ range-based for statement supported. (or c++ foreach statement) (aka. minimal code to support c++ foreach/range-based-for)

As we know from this example, to support range-based for we need:

1. container/custom-class has begin() end() method, which return a iterator or something else.
2. iterator has implemented operators:
3. not-equal operator !=, which is bool operator !=(T&)
4. pre-increment operator ++, which is T operator ++()
5. indirection operator *, which is T operator *()

References

• https://en.cppreference.com/w/cpp/language/range-for
• https://en.cppreference.com/w/cpp/language/operators
• https://stackoverflow.com/questions/8164567/how-to-make-my-custom-type-to-work-with-range-based-for-loops