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I have a char *data that is a Datagram to represent the packet I want to send in but I need to insert on that an uint8_t array.
// Datagram to represent the packet
char datagram[4096], source_ip[32], *data, *pseudogram;
// zero out the packet buffer
memset(datagram, 0, 4096);
// IP header
struct iphdr *iph = (struct iphdr *)datagram;
// UDP header
struct udphdr *udph = (struct udphdr *)(datagram + sizeof(struct ip));
// Data part
data = datagram + sizeof(struct iphdr) + sizeof(struct udphdr);
uint8_t packet_bytes[] = { 0xff, 0xff, 0x81, 0x01, 0x01 };
memcpy(data, packet_bytes, 5);
Doing this allows me to insert what I need and it works but the problem is that I have and uint8_t array with 0x00 in the middle making this harder than I thought because the 0x00 hex also means a termination of an array, how can I make it to work with this array instead ?
char packet_bytes[] = {
0xff, 0xff, 0x81, 0x00, 0x00, 0x00, 0x00, 0x30,
0x13, 0x43, 0x00, 0x01, 0x01, 0x01, 0x02, 0x00,
0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,
0x06, 0x00, 0x00, 0x10, 0x01, 0x01, 0x00, 0x63,
0x02, 0x00, 0x00, 0x03, 0x00, 0x01, 0x00, 0x05,
0x00, 0x00, 0x00, 0x0c, 0x00, 0x09, 0x04, 0x00,
0x0a, 0x00, 0x03, 0x01, 0x00, 0x11, 0x77, 0x25
};
the problem is that I have and uint8_t array with 0x00 in the middle making this harder than I thought because the 0x00 hex also means a termination of an array
There is no such thing as "termination of an array" in C. There is null termination of character arrays used as strings, but that isn't applicable here. So the memcpy part will work just fine.
You have some other problems however:
char datagram[4096], char packet_bytes[] etc
char is unsuitable, dangerous and non-portable for the purpose of holding raw binary data. Use uint8_t instead. See Is char signed or unsigned by default?
struct iphdr *iph = (struct iphdr *)datagram;
This will lead to undefined behavior because of alignment and strict aliasing. What is the strict aliasing rule? You cannot wildly type pun from a character array to another type by pointer casts (though the other way around from "any type" to character type is possible). Furthermore, your struct may contain padding, in which case it is extra non-portable and you don't want to be sending padding bytes around.
(struct udphdr *)(datagram + sizeof(struct ip)); Same problem as above.
The only reliable way to do this is either to disable struct padding and then memcpy in/out of the struct. Or alternatively write serialization/deserialization routines accessing one struct member at a time, moving it to/from the raw data.
it seems this code make my display go crazy sometimes (but only sometimes). But when I remove dat=~dat; it seems to work fine.
why?
what I am trying to do here is just make the ascii letters be the oposite: so for example:
11001000 will be:
00110111
or
10101111 would be:
01010000
the reason for doing this is that i want to have one row (the active row) in the diplay window with black on white pixels instead of opostie like the rest of the display window.
Is there some other way I could do this? (invert the numbers)
FYI: I am programing in C. Atmel studio. atmega 4809, SSD1305z display, SPI-simular interface.
void displayinvertedString(char str[], uint8_t ypos,uint8_t xpos)
{
Set_Page_Address(ypos);
Set_Column_Address(xpos);
int len = strlen(str);
uint8_t dat;
int temp;
for (int e=0; e<len; e++)
{
dat = 0xff;
Write_Data(dat); //to get an extra space between the
// numbers/letters for
//making it easier to read the text on the display
temp = str[e];
temp=temp-0x20; // As the lookup table starts from Space(0x20)
for (int w=0; w<5; w++)
{
dat= OledFontTable[temp][w]; // Get the data to be displayed for LookUptable
dat =~ dat;
Write_Data(dat);
}
}
}
----------
static uint8_t OledFontTable[][FONT_SIZE]={
//static uint8_t OledFontTable[] = {
0x00, 0x00, 0x00, 0x00, 0x00, // space
0x00, 0x00, 0x2f, 0x00, 0x00, // !
0x00, 0x07, 0x00, 0x07, 0x00, // "
0x14, 0x7f, 0x14, 0x7f, 0x14, // #
0x24, 0x2a, 0x7f, 0x2a, 0x12, // $
0x23, 0x13, 0x08, 0x64, 0x62, // %
0x36, 0x49, 0x55, 0x22, 0x50, // &
ETC. Etc.
just more raw pixel data here. this part ends like this:
0x00, 0x00, 0xFF, 0x00, 0x00, // |
0x00, 0x82, 0x7C, 0x10, 0x00, // }
0x00, 0x06, 0x09, 0x09, 0x06 // ~ (Degrees)
};
void Write_Data(unsigned char Data)
{
PORTA.OUTCLR = PIN7_bm; //cs
PORTB.OUTSET = PIN2_bm; //dc
Write_Command(Data); //
}
void Write_Command(unsigned char data)
{
SPI0.DATA = data; // copy data to DATA register
while ((SPI0.INTFLAGS & SPI_RXCIF_bm) == 0) ; //wait
}
I have asked a bit about this before. but i thought i would look "cleaner" with a new tread since info was missing from the last one.
It turned out I needed to toggle the chip select (CS) so the clock did not get out of sync with time.
The clock sync drifted with time.
It was going crazy faster for the non inverted data for some reason. But with the normal data it happend after some time also.
Thank you for the answers.
I have a structure as follows
typedef struct s_CanMsg
{
uint32_t id;
uint16_t timestamp;
uint8_t data[8];
uint8_t dlc;
bool_t isExtended;
bool_t isRemote;
} s_CanMsg_t;
and I have a structure variable as follows
s_CanMsg_t CANEraseResponse;
Now I am trying to pass an array to the data member of the structure variable as follows:
CANEraseResponse.data[8] = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00};
This is showing syntax error and how can I pass the data to the structure variable with array member? Thanks in advance.
You can initialize the whole structure when you define the variable:
s_CanMsg_t CANEraseResponse = {
some_value_for_id,
some_value_for_timestamp,
{0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00},
some_value_for_dlc,
some_value_for_isExtended,
some_value_for_isRemote
};
You can also use a designator to explicitly initialize only the array member;
s_CanMsg_t CANEraseResponse = {
.data = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00}
};
Then all other members will be initialized to zero.
And of course you can define a temporary array and copy into the structure array:
static uint8_t data[8] = {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00},
s_CanMsg_t CANEraseResponse;
memcpy(CANEraseResponse.data, data, sizeof data);
Lastly, if none of the ways above are acceptable, then the only remaining solution is to explicitly assign to each element of the array:
CANEraseResponse.data[0] = 0x00;
CANEraseResponse.data[1] = 0xFF;
CANEraseResponse.data[2] = 0x00;
CANEraseResponse.data[3] = 0x04;
CANEraseResponse.data[4] = 0x02;
CANEraseResponse.data[5] = 0x00;
CANEraseResponse.data[6] = 0x00;
CANEraseResponse.data[7] = 0x00;
The notation you are using can only be used to initialize an array. Once you declare your struct variable, you have moved past initialization. You can, however, do it with something called a "designated initializer" like so:
s_CanMsg_t CANEraseResponse = {.data= {0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00}};
CANEraseResponse.data[8] refers to the 9th element of the data member (as the array is zero based. Try removing the [8].
Edit/Clarification: removing the [8] will not solve your issue, but you should be aware that CANEraseResponse.data[8] points to a position outside of the data array.
You can't assign arrays directly in C. As well as the initialization techniques shown in other answers, you could use a compound literal and memmove() (or memcpy()):
memmove(CANEraseResponse.data, (uint8_t[]){ 0x00, 0xFF, 0x00, 0x04, 0x02, 0x00, 0x00, 0x00 }, sizeof(CANEraseResponse.data));
I am looking for a solution to concatenate in a array with value from defines and variable. I have already try with memcpy like that but it not working :
#define ADDRESS {0x00, 0x00, 0x00, 0x00, 0x00, 0x45}
#define SIGNATURE {0xC6, 0x54, 0x2D}
uint8_t packetCounter = 0;
uint8_t RadioData[2]={'2','1'};
uint8_t Packet = sizeof(uint8_t);
memcpy(Packet, ADDRESS, sizeof(ADDRESS));
memcpy(Packet, SIGNATURE, sizeof(SIGNATURE));
memcpy(Packet, packetCounter, sizeof(packetCounter));
memcpy(Packet, data, sizeof(data));
The goal of this code is to have an array with those value : ADDRESS+SIGNATURE+packetCounter+data. And I would like also to add "_" between each variable after.
Do you have any solution?
Thanks
It's not entirely clear what it is you want, but maybe something like this?
#include <stdint.h>
#define ADDRESS 0x00, 0x00, 0x00, 0x00, 0x00, 0x45
#define SIGNATURE 0xC6, 0x54, 0x2D
void Some_Function(void) {
uint8_t packetCounter = 0;
uint8_t RadioData[2]={'2','1'};
uint8_t Packet[] = {ADDRESS, SIGNATURE, packetCounter, RadioData[0], RadioData[1]};
}
Your problem is that Packet is an integer variable. The memcpy needs a pointer, not an integer variable. Your trying to copy a lot of bytes to a single byte location.
The quick and easy way worked fine for me. I see the exact bytes in the packet, in my debugger.
#include <vector>
#define ADDRESS {0x00, 0x00, 0x00, 0x00, 0x00, 0x45}
#define SIGNATURE {0xC6, 0x54, 0x2D}
uint8_t address[] ADDRESS;
uint8_t signature[] SIGNATURE;
uint8_t packetCounter = 0;
uint8_t RadioData[2] = { '2','1' };
int main() {
std::vector<uint8_t> packet;
std::copy(std::begin(address), std::end(address), std::back_inserter(packet));
std::copy(std::begin(signature), std::end(signature), std::back_inserter(packet));
packet.push_back(packetCounter);
std::copy(std::begin(RadioData), std::end(RadioData), std::back_inserter(packet));
// packet now has the bytes expected
return 0;
}
This is c++, although the question had both tags. I can put them in a malloc'ed area just as easily if you need C. Also the #define is completely unnecessary. I'd rather just define static const arrays.
I probably would have used unsigned char or char, possibly with a static assert if they need to be 8 bit.
I am trying to write a .pcap file, which is something that can be used in Wireshark.
In order to do that, I have a couple of structs with various data types I need to write to a file. (see code)
So, I create the struct instances, fill in the data, use FILE* fp = fopen("test.pcap","w"), and then I'm unsure how to properly write it to the file. I believe I should use memcpy but I'm not sure of the best way to do it. I have mostly resorted to C++ libraries in the past to do this. Any suggestions?
typedef struct pcap_hdr_s {
uint32_t magic_number; /* magic number */
uint16_t version_major; /* major version number */
uint16_t version_minor; /* minor version number */
int32_t thiszone; /* GMT to local correction */
uint32_t sigfigs; /* accuracy of timestamps */
uint32_t snaplen; /* max length of captured packets, in octets */
uint32_t network; /* data link type */
} pcap_hdr_t;
typedef struct pcaprec_hdr_s {
uint32_t ts_sec; /* timestamp seconds */
uint32_t ts_usec; /* timestamp microseconds */
uint32_t incl_len; /* number of octets of packet saved in file */
uint32_t orig_len; /* actual length of packet */
} pcaprec_hdr_t;
typedef struct ethernet_hdr_s {
uint8_t dst[6]; /* destination host address */
uint8_t src[6]; /* source host address */
uint16_t type; /* IP? ARP? RARP? etc */
} ethernet_hdr_t;
typedef struct ip_hdr_s {
uint8_t ip_hl:4, /* both fields are 4 bits */
ip_v:4;
uint8_t ip_tos;
uint16_t ip_len;
uint16_t ip_id;
uint16_t ip_off;
uint8_t ip_ttl;
uint8_t ip_p;
uint16_t ip_sum;
uint32_t ip_src;
uint32_t ip_dst;
}ip_hdr_t;
typedef struct udp_header
{
uint16_t src;
uint16_t dst;
uint16_t length;
uint16_t checksum;
} udp_header_t;
Use libpcap or WinPcap - pcap_open_dead() to get a "fake" pcap_t to use with pcap_dump_open() to specify the link-layer header type (for Ethernet, use DLT_EN10MB) and snapshot length (use 65535), pcap_dump_open() to open the file for writing, pcap_dump() to write out a packet, and pcap_dump_close() to close the file. MUCH easier than directly using fopen(), fwrite(), and fclose() (which are what libpcap/WinPcap use "under the hood").
And, yes, you have to get the byte order in the packets correct. The byte order depends on the protocol; for the type field in the Ethernet header, and for all multi-byte fields in IP, TCP, and UDP headers, they have to be in big-endian order. (The magic number in the pcap file is irrelevant to this - it only indicates the byte order of the fields in the file header and the per-packet record header, NOT the byte order of the fields in the packet, as well as, due to the way it's implemented in Linux, the meta-data at the beginning of packets in Linux USB captures. The packet data is supposed to look exactly as it would "on the wire".)
Use fwrite(). You need to check this info but I think .pcap files are written in binary mode.
Example:
pcaprec_hdr_t pcaprec_hdr;
// fill pcaprec_hdr with valid info
FILE* pFile = NULL;
pFile = fopen ("myfile.pcap" , "wb"); // open for writing in binary mode
fwrite (&pcaprec_hdr, 1, sizeof(pcaprec_hdr_t) , pFile);
fclose(pFile);
Here's my understanding of what Guy Harris is suggesting. So, as per Kyslik's request, we have:
#include <libpcap/pcap.h>
/* Ethernet/IP/SCTP INIT chunk */
static const unsigned char pkt1[82] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* ........ */
0x00, 0x00, 0x00, 0x00, 0x08, 0x00, 0x45, 0x00, /* ......E. */
0x00, 0x44, 0x55, 0xb1, 0x00, 0x00, 0x40, 0x84, /* .DU...#. */
0x26, 0x83, 0x7f, 0x00, 0x00, 0x01, 0x7f, 0x00, /* &....... */
0x00, 0x01, 0x00, 0x01, 0x1f, 0x90, 0x00, 0x00, /* ........ */
0x00, 0x00, 0x68, 0xe5, 0x88, 0x1b, 0x01, 0x00, /* ..h..... */
0x00, 0x24, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0f, /* .$...... */
0xa0, 0x00, 0x00, 0x04, 0xff, 0xff, 0x00, 0x00, /* ........ */
0x16, 0x2e, 0x80, 0x00, 0x00, 0x04, 0xc0, 0x00, /* ........ */
0x00, 0x04, 0x00, 0x0c, 0x00, 0x06, 0x00, 0x05, /* ........ */
0x00, 0x00 /* .. */
};
int main(int argc, char *argv[]) {
pcap_t *handle = pcap_open_dead(DLT_EN10MB, 1 << 16);
pcap_dumper_t *dumper = pcap_dump_open(handle, "/tmp/pktcap/cap.pcap");
struct pcap_pkthdr pcap_hdr;
pcap_hdr.caplen = sizeof(pkt1);
pcap_hdr.len = pcap_hdr.caplen;
pcap_dump((u_char *)dumper, &pcap_hdr, pkt1);
pcap_dump_close(dumper);
return 0;
}