1. Growing Arrays in C
Nathan Lee

2. The Problem Compiler statically allocates size, content int a[5];
How do we manipulate the size of arrays in C?

3. Adding Values (code) struct Nameval { char *name; int value; };
*found on page 42 of textbook
struct Nameval { char *name; int value; };
struct NVtab { int nval; int max; Nameval *nameval; } nvtab;
enum { NVINIT = 1, NVGROW = 2};

4. Adding Values (code)
int addname (Nameval newname) { Nameval *nvp; if (nvtab.nameval == NULL) { nvtab.nameval = (Nameval *) malloc (NVINIT * sizeof (Nameval)); if (nvtab.nameval == NULL) return -1; nvtab.max = NVINIT; nvtab.nval = 0; } …

5. Adding Values (code) …else if (nvtab.nval >= nvtab.max) {
nvp = (Nameval *) realloc(nvtab.nameval, (NVGROW*nvtab.max) * sizeof(Nameval));
if (nvp == NULL) return -1;
nvtab.max *= NVGROW;
nvtab.nameval = nvp; }
nvtab.nameval[nvtab.nval] = newname;
return nvtab.nval++;

6. Adding Values realloc doubles the size of the array (performance)
Adding 100 elements: growing 100 times vs growing (log2 100 ≈ 7) times
‘nvp’ is a temp value – if realloc fails
Not Sorted!

7. The Bottom Line Arrays are good for static, non-sorted allocation
We can minimize the cost of allocation in some ways
For fluctuating values and contents, don’t use arrays

8. Resources Used:
Kernighan, Brian W. and Rob Pike. The Practice of Programming Lucent Technologies.