我如何声明一个2d数组使用新?
比如,对于一个“普通”数组,我将:
int* ary = new int[Size]
but
int** ary = new int[sizeY][sizeX]
A)不工作/编译b)没有完成什么:
int ary[sizeY][sizeX]
所做的事。
我如何声明一个2d数组使用新?
比如,对于一个“普通”数组,我将:
int* ary = new int[Size]
but
int** ary = new int[sizeY][sizeX]
A)不工作/编译b)没有完成什么:
int ary[sizeY][sizeX]
所做的事。
当前回答
我使用这个不优雅,但快速,简单和工作系统。我不明白为什么不能工作,因为系统允许创建一个大尺寸数组和访问部分的唯一方法是不切割它的部分:
#define DIM 3
#define WORMS 50000 //gusanos
void halla_centros_V000(double CENW[][DIM])
{
CENW[i][j]=...
...
}
int main()
{
double *CENW_MEM=new double[WORMS*DIM];
double (*CENW)[DIM];
CENW=(double (*)[3]) &CENW_MEM[0];
halla_centros_V000(CENW);
delete[] CENW_MEM;
}
其他回答
int** ary = new int[sizeY][sizeX]
应该是:
int **ary = new int*[sizeY];
for(int i = 0; i < sizeY; ++i) {
ary[i] = new int[sizeX];
}
然后清理是:
for(int i = 0; i < sizeY; ++i) {
delete [] ary[i];
}
delete [] ary;
编辑:正如Dietrich Epp在评论中指出的那样,这并不是一个轻量级的解决方案。另一种方法是使用一个大内存块:
int *ary = new int[sizeX*sizeY];
// ary[i][j] is then rewritten as
ary[i*sizeY+j]
我在创建动态数组时使用这个。如果你有一个类或结构。这是可行的。例子:
struct Sprite {
int x;
};
int main () {
int num = 50;
Sprite **spritearray;//a pointer to a pointer to an object from the Sprite class
spritearray = new Sprite *[num];
for (int n = 0; n < num; n++) {
spritearray[n] = new Sprite;
spritearray->x = n * 3;
}
//delete from random position
for (int n = 0; n < num; n++) {
if (spritearray[n]->x < 0) {
delete spritearray[n];
spritearray[n] = NULL;
}
}
//delete the array
for (int n = 0; n < num; n++) {
if (spritearray[n] != NULL){
delete spritearray[n];
spritearray[n] = NULL;
}
}
delete []spritearray;
spritearray = NULL;
return 0;
}
如果你想声明一个预定义的指针数组:
int **x;
x = new int*[2] {
new int[2] { 0, 1 },
new int[2] { 2, 3 }
};
访问:
cout << x[0][0];
下面的例子可能会有所帮助,
int main(void)
{
double **a2d = new double*[5];
/* initializing Number of rows, in this case 5 rows) */
for (int i = 0; i < 5; i++)
{
a2d[i] = new double[3]; /* initializing Number of columns, in this case 3 columns */
}
for (int i = 0; i < 5; i++)
{
for (int j = 0; j < 3; j++)
{
a2d[i][j] = 1; /* Assigning value 1 to all elements */
}
}
for (int i = 0; i < 5; i++)
{
for (int j = 0; j < 3; j++)
{
cout << a2d[i][j] << endl; /* Printing all elements to verify all elements have been correctly assigned or not */
}
}
for (int i = 0; i < 5; i++)
delete[] a2d[i];
delete[] a2d;
return 0;
}
首先使用指针定义数组(第1行):
int** a = new int* [x]; //x is the number of rows
for(int i = 0; i < x; i++)
a[i] = new int[y]; //y is the number of columns