2-D array in C, address generation

How do addresses get generated in arrays in C, say how does a [x][y] get to a particular value, i know 开发者_StackOverflowits not that big a question but just about to actually start coding.

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Well it is done depending on your data type of whose array you have considered.

Say for an Integer array, each value holds 4 bytes, thus a row X long will take 4X bytes.

Thus a 2-D matrix of X*Y will be of 4*X*Y Bytes.

Any address say Arry[X][Y] would be calculated as : (Base Address of Arry) + (X * No. of columns) + ( Y // Offset in current row )

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2-dimensional arrays in C are rectangular. For example:

int matrix[2][3];

allocates a single block of memory 2*3*sizeof(int) bytes in size. Addressing matrix[0][1] is just a matter of adding 0 * (3 * sizeof(int)) to sizeof(int). Then add that sum to the address at which matrix starts.

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A nested array is an array of arrays.

For example, an int[][6] is an array of int[6].
Assuming a 4-byte int, each element in the outer array is 6 * 4 = 24 bytes wide.

Therefore, arr[4] gets the third array in the outer array, or *(arr + 4 * 24).

arr[4] is a normal int[]. arr[4][2] gets the second int in this inner array, or *(arr + 4 * 24 + 2 * 4)

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E.g.

char anArray[][13]={"Hello World!","February","John"};

You can visualize it as:

anArray:

H|e|l|l|o| |W|o|r|l|d|!|\0|F|e|b|r|u|a|r|y|\0|\0|\0|\0|\0|J|o|h|n|\0|\0|\0|0|\0
^                          ^                              ^
0                          13                             26