A.
sizeof(val) returns type size_t, it usually is a kind of unsigned type.
maxbytes - sizeof(val) returns value of type size_t, and it’s always >= 0
B.
/*
* copy-int.c
*/
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>
void copy_int(int val, void* buf, int maxbytes) {
/* compare two signed number, avoid someone set maxbytes a negetive value */
if (maxbytes >= (int) sizeof(val)) {
memcpy(buf, (void*)&val, sizeof(val));
}
}
int main(int argc, char* argv[]) {
int maxbytes = sizeof(int) * 10;
void* buf = malloc(maxbytes);
int val;
val = 0x12345678;
copy_int(val, buf, maxbytes);
assert(*(int*)buf == val);
val = 0xAABBCCDD;
copy_int(val, buf, 0);
assert(*(int*)buf != val);
free(buf);
return 0;
}