How to change pointers of dynamically resized array?

Question

I'm trying to increase a static array by doubling it dynamically in another array as soon as it is maxed. I planed on created new array with malloc(), then copy values over. Once done, I planned on deleting first array and then pointing first pointer to second?

float FirstArray[1];

if (first array is full) {
    float *TempArray = (float*) malloc (sizeof (float) * counter);
    for (loop) {
        TempArray[i] = FirstArray[i];
    }
    //I'm not sure how to point the static array to the dynamic one
    free(FirstArray);
    *FirstArray = &TempArray;
//i get this error with line above
//assignment makes integer from pointer without a cast
}

That's ok, but FirstArray needs to be dynamically allocated initially also. — Vaughn Cato
– Vaughn Cato, Commented Mar 3, 2012 at 23:13

Oliver Charlesworth · Accepted Answer · 2012-03-03 23:12:48Z

4

Perhaps you should consider realloc, as this is exactly why it exists.

answered Mar 3, 2012 at 23:12

Oliver Charlesworth

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Vaughn Cato · Accepted Answer · 2012-03-03 23:14:58Z

1

FirstArray needs to be dynamically allocated as well:

int counter = 1;
float *FirstArray = (float *)malloc(sizeof(float)*counter);

if (first array is full) {
float *TempArray = (float*) malloc (sizeof (float) * counter);
for (loop) {
TempArray[i] = FirstArray[i];
}
free(FirstArray);
FirstArray = TempArray;

answered Mar 3, 2012 at 23:14

Vaughn Cato

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Comments

IKavanagh · Accepted Answer · 2015-09-29 19:41:52Z

Static array allocations are managed automatically: you do not need to (and should not) allocate it, so you should not free it as well. You cannot assign a float * (pointer) to float[N] (N-elem static array) because these are considered incompatible types by the compiler. (Static array is also zeroed on init to mention one more difference.)

So basically you have two choices: forget the name FirstArray, preserve its content under new name (SecondArray?). Nonsense.. Other way is to have dynamic array from the beginnings.

uint size = 4096;
double * array = ( double * ) malloc( sizeof( double ) * size );

Then copy could be unneccessary, so use realloc as Richard and Oliver pointed out.

size <<= 1; /* double size */
array = ( double * ) realloc( ( void * ) array, sizeof( double ) * size );

Notice that input and output pointers of realloc might differ. If not, copy is spared.

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