#include <string.h>
#include <malloc.h>
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
typedef struct AA {
int a1:5;
int a2:2;
} AA;
int main() {
AA aa;
char cc[100];
strcpy(cc, "0123456789");
memcpy(&aa, cc, sizeof(AA));
printf("%d\n", aa.a1);
printf("%d\n", aa.a2);
return 0;
}
I mean I know that sizeof(AA)
is sizeof(int)
equals 4
byte, and after copying "0123"
to aa
the binary number is
00110011,00110010,00110001,00110000
3 2 1 0
but i don't understand which bits are a1:5
or a2:2
?
The arrangements of bitfields is not standardized.
Based on your results, a1
holds 10000
and a2
holds 01
. One way this could arise is if a1
is the lowest 5 bits of cc[0]
and a2
is the next-lowest 2 bits .
That is, cc[0]
is 00110000
which is being divided as 0 01 10000
.
If you did some more experimentation with values you could find out for sure which order your compiler is using.