Question

I’m supposed to write a library in c++ that should handle the connections to the kad network.
I’m trying to build a packet accordant to those used by aMule&co.

And I really can’t understand the difference between this code:

buffer = "\xe4\x20\x02";

and, for example, this code:

char p_buffer[36];
p_buffer[0] = 0xe4;
p_buffer[1] = 0x20;
p_buffer[2] = 0x02;

buffer = p_buffer;

(buffer is a private attribute of the class, while p_buffer is a local variable)

capturing the packets with wireshark gives me different results (the first one is right as I wanted, the second one not), like I was doing something wrong with little endian / big endian notations, I guess…

and why in the constructor of a class can’t I modify a [private] “char* buffer” like this:

buffer[0] = 0xe4;

? (it does not work, exits without any trace back error)

(if it can matter, I’m using crypto++ and boost libraries)

thanks in advance for any help_

Answer 1

Your first code sample is roughly equivalent to:

static const char buffer_internal[4] = { 0xe4, 0x20, 0x02, 0x00 };
buffer = buffer_internal;

The two differences here are:

• The buffer is null-terminated
• The buffer is unmodifiable. Attempting to modify it is likely to crash.

Your second sample allocates a 36-byte modifiable buffer. However said buffer will also be discarded when it goes out of scope – be very careful here that it’s not used after being freed.

As for the third sample, have you initialized ‘buffer’, if it is a pointer? You’ve not given enough information to really diagnose your error – the full class declaration and constructor would be helpful.