如何计算二维数组大小？？ - C/C++ / C语言

int   str1[]={1,2,3,4,5,6};
int   size1=sizeof(str1)/sizeof(str1[0]);
cout < <size1 < <endl;

int   str2[][5]={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
int   size2=sizeof(str2)/sizeof(str2[0][0]);
int   lines=sizeof(str2)/sizeof(str2[0]);
int   columns=size2/lines;
cout < < "the   total   number   is   " < <size2 < <endl;
cout < < "the   line   number   is   " < <lines < <endl;
cout < < "the   column   number   is   " < <columns < <endl;