[英]How can I initialize an array in C++ with a size that is given to the constructor?
I have a C++ class with a member that is supposed to be a two dimensional array.我有一个 C++ class 和一个应该是二维数组的成员。 I want to declare my array as a member in the header file of the class. Then in the constructor of my class I want to initialize my array with a size (given to the constructor) and fill it with zeros.我想将我的数组声明为 class 的 header 文件中的成员。然后在我的 class 的构造函数中,我想用一个大小(给构造函数)初始化我的数组并用零填充它。
I have a working example of what I want in java:我在 java 中有一个我想要的工作示例:
class Obj {
int[][] array;
public Obj(int sizex, int sizey) {
array = new int[sizex][sizey];
}
}
public class Main
{
public static void main(String[] args) {
Obj o = new Obj(12,20);
}
}
I do not want to mess with pointers or alloc() and free().我不想弄乱指针或 alloc() 和 free()。 As my class is supposed to be basically a wrapper for this array, I want to keep it simple.因为我的 class 基本上应该是这个数组的包装器,所以我想保持简单。
I have thought about using std::vector, but as the array is never being resized after its initialization, I feel like vector is a little overpowered... Is there a better way than this: ?我考虑过使用 std::vector,但由于数组在初始化后从未调整过大小,我觉得 vector 有点过于强大了……有没有比这更好的方法:?
#include<vector>
class Obj {
std::vector<std::vector<int>> array;
public:
Obj(int xsize, int ysize) {
std::vector<std::vector<int>> newArray(xsize, std::vector<int>(ysize, 0));
array = newArray;
}
};
int main()
{
Obj o(12,20);
}
std::vector
is the best match here. std::vector
是这里的最佳匹配。 (As you said, in most cases raw arrays and pointers could be avoided. Also see How can I efficiently select a Standard Library container in C++11? ) (正如您所说,在大多数情况下,可以避免使用原始 arrays 和指针。另请参阅How can I efficiently select a Standard Library container in C++11? )
And you can initialize the data member directly in member initializer list instead of assigning in the constructor body after default-initialization, eg您可以直接在成员初始化列表中初始化数据成员,而不是在默认初始化后在构造函数体中分配,例如
Obj(int xsize, int ysize) : array(xsize, std::vector<int>(ysize, 0)) {
}
Other than using std::vector you can just allocate memory of the required size from the heap.除了使用 std::vector 之外,您只需从堆中分配所需大小的 memory。
class Obj {
int** arr;
int x, y;
public:
Obj(int sizex, int sizey) : x(sizex), y(sizey) {
arr = new int*[sizex];
for (unsigned i = 0; i < sizex; i++) {
arr[i] = new int[sizey];
}
}
//IMPORTANT TO DELETE, OTHERWISE YOU'LL GET A MEMORY LEAK
~Obj() {
for (unsigned i = 0; i < x; i++) {
delete[] arr[i];
}
delete[] arr;
}
}
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