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alignof
ALIGNOF() macro to determine alignment of a type.
Rusty Russell <rusty@rustcorp.com.au>
Many platforms have requirements that certain types must be aligned to certain address boundaries, such as ints needing to be on 4-byte boundaries. Attempting to access variables with incorrect alignment may cause performance loss or even program failure (eg. a bus signal).
There are times which it's useful to be able to programatically access these requirements, such as for dynamic allocators.
#include <stdio.h>
#include <stdlib.h>
#include <ccan/alignof/alignof.h>
// Output contains "ALIGNOF(char) == 1"
// Will also print out whether an onstack char array can hold a long.
int main(int argc, char *argv[])
{
char arr[sizeof(int)];
printf("ALIGNOF(char) == %zu\n", ALIGNOF(char));
if ((unsigned long)arr % ALIGNOF(int)) {
printf("arr %p CANNOT hold an int\n", arr);
exit(1);
} else {
printf("arr %p CAN hold an int\n", arr);
exit(0);
}
}
CC0 (Public domain)