C++动态创建二维数组，memset()初始化二维数组

#include <iostream>
#include <string.h>

int main(void){
int n,m;
while(std::cin >>n >>m)
{
//动态创建二维数组
int **a = new int *
;
for(int i=0; i<n; ++i)
{
a[i] = new int[m];
//注意下面是第一个参数是a[i]
//第三个参数是 m*sizeof(int)
memset(a[i],0,m*sizeof(int));
}

//这两个大小都是4 int指针的大小
std::cout << sizeof(a) << " " \
<< sizeof(a[0]) << std::endl;

for(int i=0; i<n; ++i)
{
for(int j=0; j<m; j++)
std::cout << a[i][j] << " ";
std::cout << std::endl;
}

//用完之后，记得释放内存 ！！！！！
for(int i=0; i<n; ++i)
delete []a[i];
delete []a;
}
return 0;
}

#include <iostream>

int main(void)
{
int a[10];
int *b = new int[10];
std::cout << "sizeof(a) = " << sizeof(a) << \
"\nsizeof(b) = " << sizeof(b) << std::endl;
return 0;
}