C指针和访问数组

Question

It's been a while since I've had to program in C and I have completely forgotten how to work with pointers. So for my project I have to make a program that reading in a txt file and create a histogram of the numbers.

The program must be

void hist_2d(
    int *head, /* A pointer to the input tiles. */
    int w, /* The width (in pixels) of the tile. */
    int h, /* The height (in pixels) of the tile. */
    int stride, /* Number of pixels between 2 contiguous rows. */
    int *bins, /* Array of input bins for the desired histogram. */
    int m, /* The number of input bins. */
    int *out /* An array in which to store the output histogram. */
)

My question is with *head and accessing the array.

So for example the image is

[1,2,3,4,5,6;
7,8,9,10,11,12;
13,14,15,16,17,18;
19,20,21,22,23,24]

In pixels.txt it would be:

1
2
3
...

The histogram is supposed to calculated in tiles, so for my example a tile could be a 2x3 which would be:

[1,2,3;
7,8,9]

Doing the histogram part is easy its getting they data that I don't understand. From what I understand *head is an array of addresses for the starting point of each tile but how do actually get the value? and how do I get the next value?

Would head[0] get me the address or the first value?

Thank you, sorry for the long post, but I wanted to make sure I gave all the info needed.

Answer 1

Yeas, it sounds as if head is a pointer to the first element in an array of int , where each element is (perhaps) the index of the upper left corner of a tile. In your example of the 2x3 tiles (if whoever filled the array is using those numbers as indices), the array would contain [1, 4, 13, 16].

Here's how to handle the elements of an array:

int h[4];

h[0] = 1;
h[1] = 4;
h[2] = 13;
h[3] = 16;

printf("%d\n", h[0]);  // will print "1"

int n = h[2]; // the value of n is now 13

Does that clear things up?