Variable Storage

Variable Storage Memory Locations (Logical) Stack Heap Program Code Register Variable Classes Automatic (locals) Parameters Globals

Variable Types • Scalars • Arrays • Structs • Unions • Objects ?

Row Major Array Storage char A[20][15][10];

Column Major Array Storage char A[20][15][10];

OR (Row Major) char A[20][15][10];

Array Declaration Algorithm Dimension Node { int min; int max; int size; }

Declaration Algorithm (2) • Doubly linked list of dimension nodes • Pass 1 – while parsing • Build linked list from left to right • Insert min, max • Size = size of an element • Append node to end of list • min = max = size = 1

Declaration Algorithm (3)Pass 2 • Traverse list from tail to head • For each node, n, going “right” to “left” • Factor = n.max – n.min + 1 • For each node, m, right to left starting with n • m.size = m.size * factor • For each node, n, going left to right • N->right->max = max; N->right->min = min • Delete first element of list

Array Declaration (Row Major) int weight[2000..2005][1..12][1..31]; list of “dimension” nodes int min, max, size size of element of this dimension 1448 124 4

Array Offset (Row Major) Traverse list summing (max-min) * size int weight[2000..2005][1..12][1..31]; x = [2002][5][31] (2002-2000) * 1448 + (5-1) * 124 + (31-1) * 4 1448 124 4

Your Turn • Assume • int A[10][20][30]; • Row major order • “Show” A’s dimension list • Show hypothetical 3-addr code for • X = A[2][3][4] ; • A[3][4][5] = 9

Your Turn 2 • Assume • int A[10][20][30]; • Column major order • “Show” A’s dimension list • Show hypothetical 3-addr code for • X = A[2][3][4] ; • A[3][4][5] = 9

Variable Storage