How to pack struct with a byte array

问题

Im trying to pack data that resembles the following struct. Ultimately this needs to be of type NSData.

typedef struct __attribute__((packed)) {
    UInt8  a;
    UInt8  b;
    UInt8  c[17];
} myStruct;

If I try the following I get an error when assigning value to c.

myStruct str = {};
str.a = 1;
str.c = aByteArray; // `Array UInt8 [17] is not assignable.`

How can pack data by either assigning values to myStruct or constructing its equivalent using output? I think the following implementation would work for first 2 octets, but not the last array of 17 UInt8's, that also needs padding for last 2 octets. One problem looks like Im not actually assigning last 17 octets in a single array, so parser wouldn't succeed.

UInt8 a = 1;
UInt8 b = 0b00001111;

UInt8 output[] = {};
int idx = 0;
output[idx++] = a;
output[idx++] = b;
// add each
for (int i=0; i<15; i++) {
    // otherByteArray == UInt[15]
    output[idx++] = otherByteArray[i];
}
UInt8 padding = 0xAA;
output[idx++] = padding;
output[idx++] = padding;

Update This implementation seems to work, except the byteArrays do not match after the 8th index.. when they should, except for the padding.

    // Unpack
    Packet *packet = (Packet *)request.value.bytes;
    if (packet) {
        UInt8  a = packet->a;
        UInt8  b = packet->b;
        UInt8 *c = packet->c;

        for (int i=0; i<15; i++) {
            NSLog(@"c[%d]: %hhu", i, c[i]);
        }

        // Pack
        UInt8 output[20] = {};
        NSUInteger idx = 0;
        // packet num
        UInt8 a = a + 1;
        memcpy(&output[idx], &a, sizeof a);
        idx += sizeof a;
        // b
        UInt8 b = 0b01001111;
        memcpy(&output[idx], &b, sizeof b);
        idx += sizeof b;

        // c
        UInt8 result[17] = {};
        for (int i=0; i<15; i++) {
            result[i] = c[i];
        }
        UInt8 padding = 0xAA;
        result[15] = padding;
        result[16] = padding;
        memcpy(&output[idx], &result, sizeof result);
        idx += sizeof result;

        NSData *outputData = [NSData dataWithBytes:&output length:idx];

        ResponsePacket *response = (ResponsePacket *)outputData.bytes;
        UInt8 *responseC = response->c;

        for (int i=0; I<17; i++) {
            NSLog(@"responseC[%d]: %hhu", i, responseC[i]);
        }

来源：https://stackoverflow.com/questions/57659851/how-to-pack-struct-with-a-byte-array

标签

arrays

struct

pack