{"id":34112,"date":"2023-03-01T20:44:37","date_gmt":"2023-03-01T15:14:37","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-a-short-c-program-about-the-pointer\/"},"modified":"2023-03-01T20:44:37","modified_gmt":"2023-03-01T15:14:37","slug":"solved-a-short-c-program-about-the-pointer","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-a-short-c-program-about-the-pointer\/","title":{"rendered":"[Solved] A short C++ program about the pointer"},"content":{"rendered":"

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An array of arrays like yours look like this in memory<\/p>\n

\n+---------+---------+---------+---------+---------+---------+\n| x[0][0] | x[0][1] | x[0][2] | x[1][0] | x[1][1] | x[1][2] |\n+---------+---------+---------+---------+---------+---------+\n<\/pre>\n
The location of x<\/code>, x[0]<\/code> and x[0][0]<\/code> is all the same.<\/p>\n
Also, arrays naturally decays to pointers to their first element. If you use plain x<\/code> you will get &x[0]<\/code>. If you use x[0]<\/code> you will get &x[0][0]<\/code>. So when you do *x[0]<\/code> it is the same as doing *&x[0][0]<\/code>, and the dereference and address-of operators cancel each other out so you are left with x[0][0]<\/code>, which is the value you print.<\/p>\n
Furthermore, to help you understand why x<\/code> is the same as &x[0]<\/code>, you need to know that for any array or pointer<\/em> x<\/code> and index i<\/code> the expressions x[i]<\/code> is the same as *(x + i)<\/code>. That means the expression &x[i]<\/code> is the same as &*(x + i)<\/code>, and since the address-of and dereference operators again cancel each other out &x[i]<\/code> is the same as (x + i)<\/code> (or without the parentheses x + i<\/code>). Now think of the case when i<\/code> is zero, then we have &x[0]<\/code> which is the same as x + 0<\/code> which is the same as x<\/code>. So &x[0]<\/code> is the same as x<\/code>, and vice-versa.<\/p>\n
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For others that wonders what &x<\/code> and &x[0]<\/code> and &x[0][0]<\/code> are representing, please see this:<\/p>\n
\n+---------+---------+---------+---------+---------+---------+\n| x[0][0] | x[0][1] | x[0][2] | x[1][0] | x[1][1] | x[1][2] |\n+---------+---------+---------+---------+---------+---------+\n^         ^                   ^         ^\n|         |                   |         |\n+- &x     +- &x[0][1]         +- &x+1   +- &x[1][1]\n|                             |\n+- &x[0]                      +- &x[1]\n|                             |\n+- &x[0][0]                   +- &x[1][0]\n<\/pre>\n
While all of x<\/code>, x[0]<\/code>, &x<\/code>, &x[0]<\/code> and &x[0][0]<\/code> may represent the same memory address, they are semantically different, i.e they represent different types:<\/p>\n