[英]How to initialize a multi-dimensional array in a C++ constructor
I have a class that contains a few multi-dimensional arrays.我有一个 class 包含一些多维 arrays。 I am trying to initialize these arrays in the constructor, but I am having trouble figuring our how to do it.
我正在尝试在构造函数中初始化这些 arrays,但我无法弄清楚如何去做。 The array is always of a fixed size.
该数组始终具有固定大小。 Here's what I have so far:
这是我到目前为止所拥有的:
class foo {
private:
int* matrix; //a 10x10 array
public:
foo();
foo:foo() {
matrix = new int[10][10]; //throws error
}
the error I get is:我得到的错误是:
cannot convert `int (*)[10]' to `int*' in assignment
how can I accomplish this?我怎样才能做到这一点? preferably, I would like the array to default to a 10x10 array of all 0s.
最好,我希望数组默认为全 0 的 10x10 数组。
#include <memory.h>
class foo
{
public:
foo()
{
memset(&matrix, 100*sizeof(int), 0);
}
private:
int matrix[10][10];
};
That is, if you're not binding yourself to doing it with pointers (otherwise you can just pass in the pointer to memset, rather than a reference to the array).也就是说,如果您没有将自己绑定到使用指针来执行此操作(否则您可以只将指针传递给 memset,而不是对数组的引用)。
Do this:做这个:
int **matrix; //note two '**'
//allocation
matrix = new int*[row]; //in your case, row = 10. also note single '*'
for(int i = 0 ; i < row ; ++i)
matrix[i] = new int[col]; //in your case, col = 10
//deallocation
for(int i = 0 ; i < row ; ++i)
delete [] matrix[i];
delete matrix;
Advice: instead of using int**
, you can using std::vector
as:建议:您可以使用
std::vector
代替使用int**
:
std::vector<std::vector<int> > matrix;
//then in the constructor initialization list
foo() : matrix(10, std::vector<int>(10))
{ // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this is called initialization list
}
If you follow this approach, you don't need to use new
and delete
in your code.如果您遵循这种方法,则无需在代码中使用
new
和delete
。 Also, the size of matrix is 10x10
;此外,矩阵的大小为
10x10
; you can access them as matrix[i][j]
where 0<=i<10
and 0<=j<10
;您可以将它们作为
matrix[i][j]
访问,其中0<=i<10
和0<=j<10
; also note that all the elements in the matrix
is initialized with 0
.还要注意,
matrix
中的所有元素都用0
初始化。
Try this:尝试这个:
class foo
{
private:
int **matrix;
public:
foo()
{
matrix = new int*[10];
for (size_t i=0; i<10; ++i)
matrix[i] = new int[10];
}
virtual ~foo()
{
for (size_t i=0; i<10; ++i)
delete[] matrix[i];
delete[] matrix;
}
};
Until your compiler supports C++0x uniform intialization, I'm afraid you'll have to initialize each entry in the array separately if you want to do so in the initialization list.在您的编译器支持 C++0x 统一初始化之前,如果您想在初始化列表中这样做,恐怕您必须分别初始化数组中的每个条目。
What you can do however, is to not initialize but assign to the array inside your constructor (simple for loop).但是,您可以做的是不初始化而是分配给构造函数内的数组(简单的 for 循环)。
In your code you have a pointer, not an array.在您的代码中,您有一个指针,而不是一个数组。 It looks like you may want to use std::vector if you need a collection of elements that takes care of memory management for you.
如果您需要为您处理 memory 管理的元素集合,您可能想要使用 std::vector 。
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