Question

in my c application I have this typedef:

typedef double mat[2][2];

this is my declaration of function:

aaa(mat bbb, mat ccc, mat * ddd)

in my code I want to compute the sum of each member in math and write the result in ddd.
I did it over loops and this is the main line:

*ddd[i][j] = bbb[i][j] + ccc[i][j];

but I’m getting wrong result in ddd.
when I remove the pointer from ddd, I get the right result, but since I want to return it to the user by pointer I want your help.

what is wrong in my code?

Answer 1

You’re writing at the wrong address. It should be:

(*ddd)[i][j] = bbb[i][j] + ccc[i][j];

or simply change the prototype to

aaa(mat bbb, mat ccc, mat ddd)

since arrays decay to pointers anyway. ddd will be a copy, but the address it points to will be the same as the original.