What is the canonical way to create network packets in Objective C?

Question

Coming from python I could do something like this.

values = (1, 'ab', 2.7)
s = struct.Struct('I 2s f')
packet = s.pack(*values)

I can pack together arbitrary types together very simply with python. What is the standard way to do it in Objective C?

Did you check out `NSData`? – Carl Norum Mar 07 '13 at 19:29 — Carl Norum, Mar 07 '13 at 19:29
No, I have not. I will go do that, thanks. – user299648 Mar 07 '13 at 19:40 — user299648, Mar 07 '13 at 19:40

score 1 · Answer 1 · answered Mar 07 '13 at 19:30

1

Not very clear a question, but maybe you're looking for a (packed struct)?

__attribute__((packed)) struct NetworkPacket {
    int integer;
    char character;
};

answered Mar 07 '13 at 19:30

score 1 · Accepted Answer · edited Mar 07 '13 at 19:35

1

Using a C struct is the normal approach. For example:

typedef struct {
    int a;
    char foo[2];
    float b;
} MyPacket;

Would define a type for an int, 2 characters and a float. You can then interpret those bytes as a byte array for writing:

MyPacket p = {.a = 2, .b = 2.7};
p.foo[0] = 'a'; 
p.foo[1] = 'b';

char *toWrite = (char *)&p; // a buffer of size sizeof(p)

edited Mar 07 '13 at 19:35

Carl Norum

answered Mar 07 '13 at 19:30

Jesse Rusak

The other answer has a good point, too; you can use struct packing/alignment/padding to control the layout, as well as bit width specifiers, etc. – Jesse Rusak Mar 08 '13 at 12:43

2 Answers2