Ian MacArthur wrote:
> So, without any testing whatsoever, here's a guess; try this -
>
> // unsigned int a = (unsigned int)&t; // four more bytes
> union { void *pv; unsigned char a[sizeof(void*)]; } v;
> v.pv = (void *)(&t);
> // we will extract 4 more bytes from the address of t
> b[8] = v.a[0];
> b[9] = v.a[1];
> b[10] = v.a[2];
> b[11] = v.a[3];
Nice! Yes, that's definitely The Right Way in this case;
exactly what unions are for.
That compiles fine on my 64bit linux machine with -Wall,
and generates expected results. Made a test program to check it:
----
#include <stdio.h>
#include <time.h>
int main() {
time_t t = 1234;
unsigned char b[20];
union { void *pv; unsigned char a[sizeof(void*)]; } v;
v.pv = (void *)(&t);
// we will extract 4 more bytes from the address of t
b[8] = v.a[0];
b[9] = v.a[1];
b[10] = v.a[2];
b[11] = v.a[3];
printf("%p %02x %02x %02x %02x\n", (void*)&t, (unsigned int)b[8],
(unsigned int)b[9], (unsigned int)b[10], (unsigned int)b[11]);
return(0);
}
----
Result on my x64 ubuntu:
r...@delta:/var/tmp# g++ -Wall -o foo foo.cxx
r...@delta:/var/tmp# ./foo
0x7fff86b85318 18 53 b8 86
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