C - Static Array with length defined by a variable

Question

I'm actually working on an assignement in C, and for the need of my implementation, I need to use a static array, let's say

static int array[LEN];

The trick is that this array length, LEN, is computed in the main(). For example

static int LEN;

void initLen(int len) {
LEN = len;
}

static int array[LEN];

Where initLen is called in the main, and len is computed using the arguments given by the user.

The issue with this design, is that I get the error

threadpool.c:84: error: variably modified ‘isdone’ at file scope

The error is due to the fact that we cannot initialize static arrays using variables as length. To make it work, I'm defining a LEN_MAX and write

#define LEN_MAX 2400

static int array[LEN_MAX]

The issue with this design is that i'm exposing myself for buffers overflows and segfaults :(

So I'm wondering if there is some elegant way to initialize a static array with the exact length LEN?

Thank you in advance!

What is isdone and what does it have to do with your array? Nowhere in your question, except the error message, is this isdone variable mentioned. Please provide a SSCCE instead. — Some programmer dude
– Some programmer dude, Commented Apr 8, 2013 at 15:13
@JoachimPileborg well isdone is just the real array in my program, array that I simply called array in my example. — HappyRave
– HappyRave, Commented Apr 8, 2013 at 15:55

K Scott Piel · Accepted Answer · 2013-04-08 16:51:59Z

6

static int LEN;
static int* array = NULL;

int main( int argc, char** argv )
{
    LEN = someComputedValue;
    array = malloc( sizeof( int ) * LEN );
    memset( array, 0, sizeof( int ) * LEN );
    // You can do the above two lines of code in one shot with calloc()
    // array = calloc(LEN, sizeof(int));
    if (array == NULL)
    {
       printf("Memory error!\n");
       return -1;
    }
    ....
    // When you're done, free() the memory to avoid memory leaks
    free(array);
    array = NULL;

edited Apr 8, 2013 at 16:51

answered Apr 8, 2013 at 15:10

K Scott Piel

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Comments

Cloud · Accepted Answer · 2013-04-08 15:35:16Z

1

I suggest to use malloc:

static int *array;

void initArray(int len) {
   if ((array = malloc(sizeof(int)*len)) != NULL) {
      printf("Allocated %d bytes of memory\n", sizeof(int)*len);
   } else {
      printf("Memory error! Could not allocate the %d bytes requested!\n", sizeof(int)*len);
   }
}

Now don't forget to init the array before you can use it.

edited Apr 8, 2013 at 15:35

Cloud

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answered Apr 8, 2013 at 15:12

Stasel

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