c - strcpy and string presentation in memory -
i have program this(x86_64 gnu/linux)
int main() { char s[] = "123456789"; char d[] = "123"; strcpy(d, s); printf("%p, %0p\n", s, d); printf("%s, %s", s, d); return 0; } and output : 0xeb6d2930 0xeb6d2910 123456789 123456789 little confused result think program in memory this:
- '9','\0' . .
- '5','6','7','8'
- 0x7fff813af310: '1','2','3','4'
- 0x7fff813af300: '1','2','3','\0'
so result should *s = "789", *d = "123456789"
could guys explain why result isn't thought? changed format specifier %p print address of d , s know s , d overlapped there not enough space d hold s may lead undefined behaviour,but anyway wondering why result *s = "123456789" *d = "123456789"
from output show address layout , it's initial content seem be:
offset 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f d: 0xeb6d2910 30 31 32 00 xx xx xx xx xx xx xx xx xx xx xx xx | 1 2 3 . . . . . . . . . . . . . 0xeb6d2920 xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx | . . . . . . . . . . . . . . . . s: 0xeb6d2930 30 31 32 33 34 35 36 37 38 39 00 xx xx xx xx xx | 1 2 3 4 5 6 7 8 9 . . . . . . . after strcpy(d, s):
offset 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f d: 0xeb6d2910 30 31 32 33 34 35 36 37 38 39 00 xx xx xx xx xx | 1 2 3 4 5 6 7 8 9 . . . . . . . 0xeb6d2920 xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx | . . . . . . . . . . . . . . . . s: 0xeb6d2930 30 31 32 33 34 35 36 37 38 39 00 xx xx xx xx xx | 1 2 3 4 5 6 7 8 9 . . . . . . . however, d fewer memory had been allocated used during strcpy() code invokes undefeind behaviour.
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