Bit field structure arrays in C -

how can create bit-field array variable size? following code tried, didn't work.

#include <stdio.h> int main() {     int n=4;     struct bite{         unsigned a1:2;         unsigned a2:2;             :             :         unsigned a(n-1):2;         unsigned a(n):2;     }bits;      for(i=1;i<=n;i++)         bits.a[i]=i;      for(i=1;i<=n;i++)         printf("%d ",bits.a[i]);      return 0; } 

the members of struct cannot defined @ runtime.

you simulate bit array using char array , macros.

#define bitarray(array, bits) \   unsigned char array[bits / 8 + 1]  #define setbit(array, n) \   { array[n / 8] |= (1 << (n % 8)) } while (0) #define getbit(array, n) \   ((array[n / 8] >> (n % 8)) & 1)  int main(void) {   bitarray(bits, 42); /* define 42 bits , init 0s                                (in fact allocates memory (42/8 + 1) * 8 bits). */    setbit(bits, 2); /* set bit 2. */   int bit2 = getbit(bits, 2); /* bit 2 */    ... 

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similar 2-bit words per code:

#include <stdlib.h> #include <stdio.h> #include <string.h>  #define define2bitwordarray(array, two_bit_words) \   unsigned char array[two_bit_words / 4 + 1]  #define set2bitword(array, n, value) \   { array[n / 4] |= (unsigned char)((value & 0x11) << (2 * (n % 4))); } while (0) #define get2bitword(array, n) \   ((array[n / 4] >> (2 * (n % 4))) & 0x11)  int main(void) {   size_t n = 10;   define2bitwordarray(bits, n); /* define 10 two-bits words                                   (in fact allocates memory                                    (10/4 + 1) * 4 two-bit bits). */   memset(bits, 0, sizeof bits); /* set bits 0. */    for(size_t = 0; < n; i++) /* c array's indexes 0-based. */   {     set2bitword(bits, i, i);   }    for(size_t = 0; < n; i++)   {     printf("%d ", get2bitword(bits, i));   } }