最近一直被二维数组的动态内存分配和赋值搞得有点昏,还是记下来,供以后查看。
一、C++中动态分配与释放二维数组
1、二维都未知
#include <iostream>
using namespace std;
int main()
{
int **a = NULL;
int Xlength, Ylength;
cin >> Xlength >> Ylength;
/*二维数组的动态分配*/
a = new int *[Xlength];
for (int i = 0; i < Xlength; i++)
a[i] = new int[Ylength];
/*释放*/
for (int i = 0; i < Xlength; i++)
delete [] a[i];
delete a;
return 0;
}
2、已知第二维
#include <iostream>
using namespace std;
int main()
{
const int Ylength = 6;
int (*a)[Ylength];
int Xlength;
cin >> Xlength;
/*动态分配*/
a = new int[Xlength][Ylength];
/*释放*/
delete[] a;
return 0;
}
3、已知第一维
#include <iostream>
using namespace std;
int main()
{
const int Xlength = 3;
int *a[Xlength];
int Ylength;
cin >> Ylength;
/*动态分配*/
for (int i = 0; i < Xlength; i++)
a[i] = new int[Ylength];
/*释放*/
for (int i = 0; i < Xlength; i++)
delete[] a[i];
return 0;
}
4、已知第一维(保持内存的连续性)
#include <iostream>
using namespace std;
int main()
{
const int Xlength = 3;
int *a[Xlength];
int Ylength;
cin >> Ylength;
/*动态分配*/
a[0] = new int[Ylength*Xlength];
for (int i = 1; i < Xlength; i++)
a[i] = a[i-1]+Ylength;
/*释放*/
delete[] a[0];
return 0;
}
二、C中动态分配与释放二维数组
1、二维都未知
#include <stdio.h>
int main()
{
int **a = NULL;
int Xlength, Ylength;
scanf("%d%d", &Xlength, &Ylength);
/*分配二维数组*/
a = (int **)malloc(Xlength*sizeof(int *));
for (int i = 0; i < Xlength; i++)
a[i] = (int *)malloc(Ylength*sizeof(int));
/*释放*/
for (int i = 0; i < Xlenght; i++)
free(a[i]);
free(a);
return 0;
}
2、已知第二维
#include <stdio.h>
int main()
{
int (*a)[Ylength];
a = (int (*)[Ylength])malloc(sizeof(int *)*Ylength);
free(a);
return 0;
}
3、已知第一维
#include <stdio.h>
int main()
{
const int Xlength = 3;
int *a[Xlength];
int Ylength;
cin >> Ylength;
/*动态分配二维数组*/
for (int i = 0; i < Xlength; i++)
a[i] = (int *)malloc(sizeof(int)*Ylength);
/*释放*/
for (int i = 0; i < Xlength; i++)
free(a[i]);
return 0;
}
4、已知第一维(保持内存的连续性)
#include <stdio.h>
int main()
{
const int Xlength = 3;
int *a[Xlength];
int Ylength;
cin >> Ylength;
/*动态分配*/
a[0] = (int *)malloc(sizeof(int)*Xlength*Ylength);
for (int i = 1; i < Xlength; i++)
a[i] = a[i-1]+Ylength;
free(a[0]);
return 0;
}
三、三维数组的动态分配和释放
int ***array3D;
//假定数组第一维为m, 第二维为n, 第三维为h
//动态分配空间
array3D = new int **[m];
for( int i=0; i<m; i++ )
{
array3D[i] = new int *[n];
for( int j=0; j<n; j++ )
{
array3D[i][j] = new int [h];
}
}
//释放
for( int i=0; i<m; i++ )
{
for( int j=0; j<n; j++ )
{
delete array3D[i][j];
}
delete array3D[i];
}
delete array3D;
总结:
C++中使用new来分配地址的话,使用new则去掉一个*号等号右边需加上一个[](中括号,需加上维度)
注:
C和C++中函数参数传递二维数组
int a[m][n];
void func(int (*a)[n]);
int main()
{
func(&a);
return 0;
}
但C++中可以使用vector传递二维数组
vector<vector<int> > a;
void func(vector<vector<int> > &a);
int main()
{
func(a);
return 0;
}