The following sets byte
to 1 on big-endian and 0 on little-endian.
uint16_t word = 0x0001;
uint8_t byte = *(((uint8_t *)&word) + 1);
Is there any way to get the address of the low or high byte that is cross-platform safe?
Since C99, code could use a compound literal to find the MSByte address offset.
Let the compiler form efficient code.
Below uses a 4-byte example to help illustrate adherence with big, little and PDP endian.
int main() {
uint32_t word = 0x12345678;
printf("%p\n", (void*)&word);
for (unsigned i=0; i<sizeof word; i++) printf("%x\n", ((uint8_t*) &word)[i]);
uint8_t *msbyte_address = ((uint8_t*) &word) + //
// v----------------------------------------------------v compound literal
( union { uint32_t u32; uint8_t u8[4]; }) {0x00010203}.u8[0];
// value at 1st byte ^---^
printf("%p\n", (void*)msbyte_address);
}
Example output (little endian)
0xffffcbfc
78
56
34
12
0xffffcbff
For uint16_t
uint16_t word = 0x1234;
uint8_t *msbyte_address = ((uint8_t*) &word) +
( union { uint16_t u16; uint8_t u8[2]; }) {0x0001}.u8[0];