Multidimensional Arrays

[Terry]

Hi,

can someone plz tell me how multidimensional arrays (like a 2-D array)
are stored in memory? Are they like single dimensional arrays? Stored
sequentially in one "row", so to say?

Thanks

Terry

 

[Mike Wahler]

Hi,

can someone plz tell me how multidimensional arrays (like a 2-D array)
are stored in memory?

C doesn't really have 'multidimensional' arrays. What
looks like one is really an 'array of arrays'.

Arrays (however many 'dimensions') are stored in contigous
memory locations.

Are they like single dimensional arrays? Stored
sequentially in one "row", so to say?

An array:

int arry[2][3];

is stored thus:

Low High
address address
[0][0], [0][1], [0][2], [1][0], [1][1], [1][2]

-Mike

 

[Julian V. Noble]

Hi,

can someone plz tell me how multidimensional arrays (like a 2-D array)
are stored in memory? Are they like single dimensional arrays? Stored
sequentially in one "row", so to say?

Thanks

Terry

C and most modern languages store 2D arrays "row-wise". That is, if
S is the data size in storage units, and W is the number of items in
a row, the actual address of the i,j 'th item is

A[0][0] + S*(i+W*j)

of course a real C maven would express the above differently,
probably with pointers, but you see what I mean.

Fortran, BTW, stores data column-wise. This is a problem for people
who have to link compiled Fortran library functions to C or vice
versa.



--
Julian V. Noble
Professor Emeritus of Physics
(e-mail address removed)
^^^^^^^^^^^^^^^^^^
http://galileo.phys.virginia.edu/~jvn/

"Science knows only one commandment: contribute to science."
-- Bertolt Brecht, "Galileo".