c sizeof

#include "iostream"
using namespace std;

int  main(int argc, char const *argv[]){
	int *a[2][3];
	printf("sizeof(*a[0][0]) is %lu\n", sizeof(*a[0][0]));
	printf("sizeof(a[0][0]) is %lu\n", sizeof(a[0][0]));
	printf("sizeof(*a[0]) is %lu\n", sizeof(*a[0]));
	printf("sizeof(a[0]) is %lu\n", sizeof(a[0]));
	printf("sizeof(*a) is %lu\n", sizeof(*a));
	printf("sizeof(a) is %lu\n", sizeof(a));
	return 0;
}

the result is :

sizeof(*a[0][0]) is 4
sizeof(a[0][0]) is 8
sizeof(*a[0]) is 8
sizeof(a[0]) is 24
sizeof(*a) is 24
sizeof(a) is 48
[Finished in 0.4s]

分析：a为一个二维的指针数组，其中的每一个元素为一个指针，指向一个int型的值。

a[0][0]	a[0][1]	a[0][2]
a[1][0]	a[1][1]	a[1][2]

a指向整个数组区域。（64bit系统中，指针占8bit）

*a同a[0]，都指向数组a的第一行

*a[0]同a[0][0]，都指向数组a的第一行的第一个元素

*a[0][0]为元素a[0][0]指向的int型的值