make a single buffer using memcpy

Asked Apr 02 '17 at 15:05

Active Apr 02 '17 at 15:09

Viewed 33 times

I am writing a C++ code. here The goal of the program is to create single buffer from two or three different buffers. Here is the code I wrote.

#include <iostream>
#include <cstdint>
#include <cstring>

int main()
{
    uint8_t LLDP_STANDARD_DST_MAC_STRING [] = {0x01,0x80,0xc2,0x00,0x00,0x0e};
    uint16_t LLDP_EtherType={ 0x88CC};`
    uint8_t* buf=new uint8_t[14];`
    uint8_t LLDP_STANDARD_SRC_MAC_STRING[] = {0x11,0x81,0xC3,0x01,0x01,0x1e};`
    memcpy(buf,&LLDP_STANDARD_DST_MAC_STRING,6);
    memcpy(buf+sizeof(LLDP_STANDARD_DST_MAC_STRING),&LLDP_STANDARD_SRC_MAC_STRING,6);

    std::cout << "first data " << sizeof(buf) << std::endl;
    std::cout << "firt data " << (uint8_t) buf[12] << std::endl;
}

When I run the code, size of buf the code is priting 8. It is wrong? The value is not clear text. some different charatcter.

Thanks for your help.

Best regards Sothy

edited Apr 02 '17 at 15:09

DeiDei

10,205
6
55
80

asked Apr 02 '17 at 15:05

sothy

Please format your code properly. – Apr 02 '17 at 15:08
`buf` is a pointer `sizeof` a pointer is the size of the pointer on your architecture. – Richard Critten Apr 02 '17 at 15:14
You have a 64-bit system. The size of a pointer on your system is 8 bytes. Not surprising. The `sizeof` operator clearly doesn't do what you think it does. Time to check the documentation. – Cody Gray - on strike Apr 02 '17 at 15:14
@CodyGray typo 8 bytes ;) – Richard Critten Apr 02 '17 at 15:14
Thanks, @Richard, got that fix in just in time! – Cody Gray - on strike Apr 02 '17 at 15:15
8 is the size of the pointer – Andrei Damian Apr 02 '17 at 15:15
My question is that how to find the size of array? array is buf. what function I can use? thanks – sothy Apr 02 '17 at 15:27
@sothy: Why don't you _read_ the page you were linked to quarter of an hour ago? – Lightness Races in Orbit Apr 02 '17 at 15:29
@sothy you created a dynamic array, you either need to: remember the size you created it; or use `std::array`; or use `std::vector`. – Richard Critten Apr 02 '17 at 15:50
@Richard, I got the point. Now Another question, I try to retrieve the data from buf. Data seems not understandable buf[0] is ok for retrieving the data from buf? which cast I have to use? – sothy Apr 02 '17 at 15:53
If you have another question, please ask in a new question. – Richard Critten Apr 02 '17 at 19:29

make a single buffer using memcpy

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