我有一个名为mat [3] [3]的类的私有成员,我希望能够在我的课程之外访问这个3×3数组(只读它,而不是更改).是否可以编写返回指向我的数组的指针的访问器方法?我怎样才能做到这一点?请提供代码示例.
这是我的班级:
class myClass { private: int mat[3][3]; public: return_value get_mat(void); };
我知道我可以用类似的东西
int get_mat(int i,int j);
逐个访问数组中的每个int,但为数组的每个成员调用访问器是不是很低效?
解决方法@H_404_14@
Is it possible to write accessor method that returns pointer to my array? How can I do this?
这是一种方式:
#include <iostream>
#include <algorithm>
#include <iterator>
class myClass {
public:
const int* operator[](size_t i) const {
return mat[i];
}
int* operator[](size_t i) {
return mat[i];
}
int* get_mat() {
return &mat[0][0];
}
const int* get_mat() const {
return &mat[0][0];
}
private:
int mat[3][3];
};
int main()
{
using namespace std;
myClass m;
m[0][1] = 6;
cout << m[0][1] << endl;
fill(m.get_mat(),m.get_mat() + 9,11);
copy(m.get_mat(),ostream_iterator<int>(cout,","));
cout << endl;
return 0;
}
but wouldn’t it be inefficient to call the accessor for every member of the array?
幸运的是,没有.在发布版本中,您的编译器将比您可能想象的更好地优化所有这些.
优雅地表达你的意图.允许编译器为您编写最佳代码(它会).
预期产量:
6
11,11,
当我们开始充实矩阵类时,我们可能希望开始构建针对缓冲区溢出的一些安全措施(此代码可能需要c 14)…
#include <iostream>
#include <algorithm>
#include <iterator>
#include <functional>
#include <random>
#include <cassert>
template<class T,size_t N>
struct safe_array_ref
{
constexpr safe_array_ref(T* data) : _data(data) {}
constexpr T& operator[](size_t i) const noexcept {
assert(i < N);
return _data[i];
}
constexpr T* begin() const {
return _data;
}
constexpr T* end() const {
return _data + N;
}
constexpr size_t size() const {
return N;
}
private:
T* _data;
};
class myClass {
public:
auto operator[](size_t i) const {
// provide some degree of safety
assert(i < extent_1);
return safe_array_ref<const int,extent_2>(mat[i]);
}
auto operator[](size_t i) {
// provide some degree of safety
assert(i < extent_1);
return safe_array_ref<int,extent_2>(mat[i]);
}
int* get_mat() {
return &mat[0][0];
}
const int* get_mat() const {
return &mat[0][0];
}
const int* begin() const {
return get_mat();
}
const int* end() const {
return get_mat() + total_extent;
}
int* begin() {
return get_mat();
}
int* end() {
return get_mat() + total_extent;
}
constexpr size_t size() const {
return total_extent;
}
private:
int mat[3][3];
public:
constexpr static size_t extent_1 = std::extent<decltype(mat)>::value;
constexpr static size_t extent_2 = std::extent<std::remove_extent_t<decltype(mat)>>::value;
constexpr static size_t total_extent = extent_1 * extent_2;
};
int main()
{
using namespace std;
myClass m;
m[0][1] = 6;
cout << m[0][1] << endl;
generate(m.begin(),m.end(),bind(uniform_int_distribution<int>(0,99),default_random_engine(random_device()())));
// copy the whole matrix to stdout
copy(m.begin(),"));
cout << endl;
// copy one row/column of the matrix to stdout
copy(m[1].begin(),m[1].end(),"));
cout << endl;
return 0;
}
样本输出:
6
76,6,39,68,40,77,28,76,
Is it possible to write accessor method that returns pointer to my array? How can I do this?
这是一种方式:
#include <iostream> #include <algorithm> #include <iterator> class myClass { public: const int* operator[](size_t i) const { return mat[i]; } int* operator[](size_t i) { return mat[i]; } int* get_mat() { return &mat[0][0]; } const int* get_mat() const { return &mat[0][0]; } private: int mat[3][3]; }; int main() { using namespace std; myClass m; m[0][1] = 6; cout << m[0][1] << endl; fill(m.get_mat(),m.get_mat() + 9,11); copy(m.get_mat(),ostream_iterator<int>(cout,",")); cout << endl; return 0; }
but wouldn’t it be inefficient to call the accessor for every member of the array?
幸运的是,没有.在发布版本中,您的编译器将比您可能想象的更好地优化所有这些.
优雅地表达你的意图.允许编译器为您编写最佳代码(它会).
预期产量:
6 11,11,
当我们开始充实矩阵类时,我们可能希望开始构建针对缓冲区溢出的一些安全措施(此代码可能需要c 14)…
#include <iostream> #include <algorithm> #include <iterator> #include <functional> #include <random> #include <cassert> template<class T,size_t N> struct safe_array_ref { constexpr safe_array_ref(T* data) : _data(data) {} constexpr T& operator[](size_t i) const noexcept { assert(i < N); return _data[i]; } constexpr T* begin() const { return _data; } constexpr T* end() const { return _data + N; } constexpr size_t size() const { return N; } private: T* _data; }; class myClass { public: auto operator[](size_t i) const { // provide some degree of safety assert(i < extent_1); return safe_array_ref<const int,extent_2>(mat[i]); } auto operator[](size_t i) { // provide some degree of safety assert(i < extent_1); return safe_array_ref<int,extent_2>(mat[i]); } int* get_mat() { return &mat[0][0]; } const int* get_mat() const { return &mat[0][0]; } const int* begin() const { return get_mat(); } const int* end() const { return get_mat() + total_extent; } int* begin() { return get_mat(); } int* end() { return get_mat() + total_extent; } constexpr size_t size() const { return total_extent; } private: int mat[3][3]; public: constexpr static size_t extent_1 = std::extent<decltype(mat)>::value; constexpr static size_t extent_2 = std::extent<std::remove_extent_t<decltype(mat)>>::value; constexpr static size_t total_extent = extent_1 * extent_2; }; int main() { using namespace std; myClass m; m[0][1] = 6; cout << m[0][1] << endl; generate(m.begin(),m.end(),bind(uniform_int_distribution<int>(0,99),default_random_engine(random_device()()))); // copy the whole matrix to stdout copy(m.begin(),")); cout << endl; // copy one row/column of the matrix to stdout copy(m[1].begin(),m[1].end(),")); cout << endl; return 0; }
样本输出:
6 76,6,39,68,40,77,28,76,