C++ :: Building Multicast Packet - Memcpy Casting
Aug 19, 2014
I am just getting back in to C++ after 10 years not doing any, contributing to an open source project. I'm adding in some functionality and am hitting a road block.
I need to send a multicast packet out on the network that is structured in a certain way. I have the definition, and know what data is going in each byte. I can successfully send a message using multicast, I now just need to send the right message.
I have used a char array to hold the message, as each char represents 1 byte, and I can transmit the array.
I am having trouble putting all of the data in the right place though. If my source data is a string, then I seem to be able to convert it, but if it is a short or int, then I keep getting errors when compiling. Similarly, two of the lines, (version and type) i initially tried using char arrays with a length of one.
Should I be using memcpy or a different function, or even be doing this in a totally different way altogether? This is the code that I am using, along with the packet structure:
//Construct a Zone Query packet
// 4 bytes - Signature "Ohz " = 0x6f, 0x68, 0x7a, 0x20
// 1 bytes - Version = 1
// 1 bytes - Type (0 = Zone Query, 1 = Zone Uri)
// 2 bytes - Entire message length = 12 + zone length
// 4 bytes - Length in bytes of the zone ID
// n bytes - Zone ID to query
[Code] ....
The errors that I get are:
error: invalid conversion from ‘short int’ to ‘const void*’ [-fpermissive]
memcpy(buffer + 6, packetLength, sizeof(packetLength));
^
[Code] ....
View 9 Replies
ADVERTISEMENT
Jun 20, 2014
I habe a program, that can send and receive UDP Multicast telegrams. When I open the socket then I bind my multicast group address and the local port to a specified networkcard (our PC has 2 network cards). Now I have a special constellation:
Our PC has 2 network cards. Multicast group 1 shall use card 1 and group shall use card 2. As long as both groups use different local ports it works fine. But when both group want to use the same port number then I can receive and send telegrams only through the first group that was created. For the second one I don't even get a FD_READ event at all.
Code:
SrvAddr.sin_family = AF_INET;
SrvAddr.sin_port = htons( (WORD) nLocalPort );
SrvAddr.sin_addr.s_addr = inet_addr(strOwnIpAddress); // bind multicast group socket to a specified networkcard
// If bind socket to port failed
if( bind( hSocket,
[Code] .....
View 2 Replies
View Related
Nov 13, 2013
I have a problem with UDP Multicast. I managed to send UDP Multicast telegrams and receive them. But when I receive the telegram I need to find out to which multicast group address it was sent. So far I have:
Code:
recvfrom( hSocket,
pcData,
nMaxDataLen,
0,
(SOCKADDR*) &from,
&len);
When I read from.sin_addr.S_un.S_addr; then I get the original IP Adresse from the sender PC but I also would like to know to which group address it was sent. Is there a way to get this infoamtion?
View 3 Replies
View Related
Feb 13, 2014
I am trying to add data to a queue with the following simplified code:
Code:
typedef struct Queue {
void * data;
int head;
int tail;
int elementSize;
My question is, how do I move the queue->data pointer to the correct memory location in order to copy given data to head? The code above inside memcpy gives med the error: "expression must be a pointer to a complete object type".
Do I need an extra pointer to be able to navigate between the queue's head and tail, and keep queue->data as a reference to the first byte of the allocated memory, or is it possible with only queue->data?
Edit. Just noticed I have mixed up head and tail. The enqueued data should probably go to the Queue's tail and not the head. However, the problem is still the same.
View 2 Replies
View Related
Apr 26, 2012
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/libstdc++.so: undefined reference to `memcpy@GLIBC_2.14'
Why is this happening and how do I fix it? I installed g++ with rpms, and all of the dependencies were handled.
glibc-headers-2.5-34
glibc-devel-2.5-34
libstdc++-devel-4.1.2-44
gcc-4.1.2-44
gcc-c++-4.1.2-44
I don't understand how memcpy can't be there, it's been standard for 40 years. And I'm not using memcpy in my code, it's likely coming from one of the STL containers I use.
View 7 Replies
View Related
Jun 19, 2013
I load an image(768*256) using a file path(OpenImageFilePath).
After load an image, I start to read the loaded Image data using GetBits method and plot the same image data(768*256).
I'm using the memcpy method, for that i'm getting the below error. memmove function also giving the same error message.
File Name : memcopy.asm
rep movsd ;N - move all of our dwords
Code for your reference
Code:
void CDlg :: FileOpen() {
CFileException CFileEx;
CStdioFile ReadFile;
// szFilters is a text string that includes two file name filters:
TCHAR szFilters[]= _T("Image Files (*.bmp)");
[code]....
View 14 Replies
View Related
Jul 21, 2013
Code:
#include<stdio.h>
#include<string.h>
int main(void) {
char str[20] = "HELLOSIR";
memcpy( str + 2 , str + 1 , 4 );
puts( str );
return 0;
}
If I have understood well the above code can be a typical example that decribes a memory overlap. Some of data to the destination (str + 2 ) will be copied before its copy.
Code: void *memcpy( void * restrict s1, const void * restrict s2, size_t n );
According to the above example I think there is no quarantee even the restrict to the pointer that we won't have overlap.It is legal to use the same pointer and not other in order to have access on the data.So for this the behaviour is not undefined right?
But how memcpy works? I mean I am taking
Code: HEELLOIR as output rather than
Code: HEEEEEIR So the behaviour due to overlap is undefined?
The const on const void * restrict s2 denotes that data can't change from s2 itself?
View 5 Replies
View Related
Nov 6, 2013
Despite seeing the correct data in gdb when I
Code:
p *(DownloadFileChunkResponse.DownloadFileChunkResult)->__ptr@100
The following C code gives me a SEG FAULT
Code:
calloc(NewMediaChunk, ChunkSize);
memcpy((void *)NewMediaChunk,
*(DownloadFileChunkResponse.DownloadFileChunkResult)->__ptr, ChunkSize);
How I got this wrong. BTW The data I am attempting to memcpy is the frontend of an MP4 file containing a number of NULLS.
Code: 00 00 00 30ftypmp42 00 00 00 00mp42mp41 00 00 dfree
BTW ChunkSize is 64000
View 9 Replies
View Related
Oct 30, 2013
I have a socket connection already set up, my thing is what would be the best way to send a packet through sockets? My teacher wants us to convert the packet to bits first before we send it. I think he wants something like this:
Code:
struct packet{
int header
int message
int flag
}clientpacket; m
My question is how do we covert this to bits, before sending it. One of my friends said we can create a char[] array the size of the struct as a buffer. will memcpy() change the struct to bits if I copy it to the buffer?
this is how is suppose to look in bits for the header field/column.
Field : header
Field size(bits): 8
data format: Unsigned int
value example: 1
Value in bits: 0000 0001
I am confused, I think I send a structure over the socket but I did not convert it to bits before I sent it .
View 13 Replies
View Related
Jan 8, 2014
How can header info 'foo' be combined with data in buffer 'buff' to pass to sendto function
Code:
/* Send a single RTP packet, converting the RTP header to network byte order. */
int sendrtp(int fd, struct sockaddr_in ........ockAddr, struct rtpheader *foo, void *data, int len)
{
char *buff = alloca(len+sizeof(struct rtpheader));
foo->b.sequence = htons(foo->b.sequence);
foo->timestamp = htonl(foo->timestamp);
foo->ssrc = htonl(foo->ssrc);
}
[code]....
View 2 Replies
View Related
Mar 6, 2015
how to send datapackets. When we send a data packet from device to another, say I have a "string". How Do I send it? Are data sent as a hex or binary number?If so do i first convert the "string" into hex or binary and then send it over the communication medium(say UART)??
I have two hex numbers to be sent using the UART, do i wrap it in some specific form and send it and retrieve it on the other side?Say if I have a data structure, in that case how do i send it? Sending data packets is very cruicial in an embedded system.
View 3 Replies
View Related
Aug 12, 2014
have udp server-client application written in C. On the client side packet loss is detected using recvfrom function and sequence numbers of packets. How can I now simulate dropped packet's on the client side, for example if server is sending 1000 packet I want to drop 20% of them? I want to do this in the code, not for example using ip tables or WANEM or something like that. And one more thing, I have few clients and I want that they can dropped different packets, not the same one.
Code:
while(1){
nbytes = recvfrom(socket, buffer, MAX_SIZE, 0, (struct sockaddr *) &srv_addr, &addrlen);
if (nbytes != -1) {
// packet is received
}else{
//packet is not received
}
}
View 2 Replies
View Related
Dec 15, 2014
Questions : I am running a client Server Program whose Sender and Receiver loop is given below .I have multi threaded Sender using OMP .As per My logic Receive should receive same amount of data send by Sender ,But its receiving more packet than Sender sent .I am not able to identify the Bug !!
Code:
/*
Running As Follow :
gcc UTGen.c -o Sender
gcc UTGen.c -o Receiver
./Receiver -m 0 -p 5000 -z 256 -P t
export OMP_NUM_THREADS=4
./Sender -m 1 -s localhost -p 5000 -z 256 -T 10 -P t
*/
[Code] .....
View 3 Replies
View Related
Apr 16, 2015
This question is kind of a continuation of Winsock Sending X264 Nal Unit. I was finally able to solve that problem, turns out in the end I was missing a memcpy(). Now my current issue is, when I try to decode the received packets, I am shown a bunch of errors. I have attached a picture with my decoding errors. So since I am using a reliable multicast socket, which doesn't guarantee order of delivery. My initial thought is that I am getting packets out of order.
So my question is, how would I attach a packet header to my current data? Could I get away with sending the header separately? Similar to what I am doing with the nal length. If I do attach my header to the packet data, what is a good way to delimit the two?
Server:
#include <WinSock2.h>
#include <WS2tcpip.h>
#include "wsrm.h"
#include <Windows.h>
#include <stdio.h>
#include <stdint.h>
#include <iostream>
#include "x264Encoder.h"
[Code] ....
My client is just reading packets into a vector, because decoding it right away was too slow. So I thought that might have been an issue, so I decided to read in 200 packets just for testing purposes.
Attached image(s)
View 6 Replies
View Related
Dec 17, 2014
I want to calculate the total some of delay pf receiving Side Packet . Code is as Follow ..
What is weird that even if i invoke a sleep of 2 sec ,than its show delay always zero. Delay will be in microsec ..Is there any problem with logic or anything else..
Code:
do
{#pragma omp parallel private(nthreads, tid) {
/* Obtain thread number */
tid = omp_get_thread_num();
if (tid == 0) {
nthreads = omp_get_num_threads();
[Code]...
View 2 Replies
View Related
Dec 26, 2014
I have Build code for sending/receiving TCP Traffic over c Socket . Now I want t add HTTP Protocol to it .
After searching out on google ,one method I found which is by GET method to send a query to a server like google.com and request a page .
But ,Suppose I saved a HTML page in my directory how can I send HTTP packet via client/server in socket using this HTML page .
View 4 Replies
View Related
Dec 27, 2014
I have code for sending/receiving TCP traffic over C socket. Now I want to add HTTP protocol to it. After searching the web, one method I found which is by GET method to send a query to a server like google.com and request a page.
But, suppose I saved a HTML page in my directory how can I send HTTP packet via client/server in socket using this HTML page.
Server side code:
sockfd = socket(AF_INET, SOCK_STREAM, 0);
bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
listen(sockfd,5);
newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr,&clilen);
while (1)
[Code] .....
View 1 Replies
View Related
Jan 19, 2014
I am programming in c++ with 'winpcap' . I read a .pcap file and after I want to get the source and destination of packets in that file. Here is a piece of my code:
Code:
////I define the sructures here
#pragma pack(1)
struct sniff_ethernet {
u_char ether_dhost[ETHER_ADDR_LEN]; /* Destination host address */
u_char ether_shost[ETHER_ADDR_LEN]; /* Source host address */
u_short ether_type; /* IP? ARP? RARP? etc */
[Code] ....
but the result is incorrect? where is the problem?
View 5 Replies
View Related
Mar 18, 2014
I'm trying to cast a float to an unsigned int and getting some surprising behavior.
Code:
float x = -1.0;
unsigned int y = (unsigned int)x;
printf("y = %d
", y);
The output of this code changes depending on which compiler I use. Sometimes I get -1 and sometimes I get 0. Not really sure why though.
View 5 Replies
View Related
Jun 8, 2013
Let's say I have a product that needs service after 500 hours at 100 RPM. I can dsiplay the remaining hours only as an integer and we only have integer math. Management wants it to display 500 for the first hour, not 499 after the first minute is ticked off. But after a few minutes fullHours will be 499 and partialHours will have some value. I have 3 ways to determine displayHours to suit management and I want to know if the first is ligit.
short fullHours = 500;
short partialHours = 0;
short displayedHours = 0;
// Method 1 - Is is Kosher to cast a boolean as an int? Is TRUE always a 1 or is that a bad assumption?
displayedHours = fullHours + (short) (partialHours != 0);
//Method 2 - Works but some have disdain for the ternary conditional
displayHours = fullHours + (partialHours ? 1 : 0);
//Method 3 - seems a bit pedantic
displayHours = fullHours;
if (partialHours != 0) {
displayHours++;
}
View 19 Replies
View Related
Apr 12, 2013
I find type casting to be very hard to grasp, I am not sure why. I understand how it works I suppose, but I find it hard to grasp why it would be needed in programming. So my question is, how often is type casting used in general programs? Is there an easier way I could be trying to teach myself about it? I am just using the tutorials provided by this site.
View 2 Replies
View Related
Apr 30, 2014
I'm writing a small piece of code that increments through a string of numbers. For every 5 numbers a product is produced. However i'm having an issue understanding an error that keeps occurring.
#include <iostream>
#include <string>
#include <cstdlib>
[Code].....
if you look at the code i've got a string with 5 numbers 1-5 for testing. As the loop increments through the string it takes the first 5 characters and converts them to integers and then a product is returned. The issue is that instead of storing the single letter at position J its storing some combination from the string and as a result gives me a huge product. I tried debugging. I checked what the string[j] value was with a simple cout << and it returned the right number. I even returned the char value before it was converted into an integer and it was the right number.
View 3 Replies
View Related
Jan 3, 2015
double a = 1.0 + 1 + 1.0f; //everynumber will be added up as a double even the last one which is a float. All 3 numbers will turn into 3.0 as a double.
int x = (int)(7 + 3.0 / 4.0 * 2); //the variable will do the math bracket first. then the va type will still be an int because int was never changed.
Console.WriteLine((1 + 1) / 2 * 3); // 1 + 1 will be done first then 1 / 2 then * by 3
Console.WriteLine(x);
Console.ReadKey();
I THINK THATS ALL WRONG ^ =/ like the comments
double a = 1.0 + 1 + 1.0f;
In this equation, everything is using addition, so we start working left to right. 1.0 + 1 is the first step. These two representations of 1 aren't the same type though. In fact, none of the three are.
The first is a double, the second is an int, and the last is a float.
So in order to do 1.0 + 1, we need to convert one type to another. Since the double type is "wider" than the int type, we'll move things up to the double type. We'll convert the int version to a double, and to 1 + 1 using double types, resulting in 2.0 as a double.
Next we do the other addition. This has the same problem, though, because we'll be adding our result from the first step (a 2 as a double) to a float. So again, the float gets converted up to a double and we do the addition using doubles.
We now have a value of 3 that is the double type, which we can simply store in our a variable without any conversions at all, since our value is already a double type.
View 4 Replies
View Related
Mar 14, 2014
So, I've used int to float cast before. And it makes sense that it preserves the int value just converts it. I don't really need the answer, I'm just interested, and a resources could suffice.
1. Why in my test program it seems to preserve the int value, I expect that, but why for 0x8000 is it registering bit negation also. I know that is the negative bit for float, but it seems wrong. Is this an error in the gcc compiler conversion code?
2. What is the documentation on these type cast on how they actual work.
3. I know like no assembly, I'm wondering if some of the built in routines to handle or is it all c side code.
4. Can I convert type and preserve the bits. Maybe use void* casting ? I've never really bothered with void* so I don't all that I can do. Except be a pointer that doesn't know the type, obviously. I tested that out in the second code, the output doesn't seem correct, except -0.000. Is it working and my test numbers just are improper float format? It can't be that I test 0x3E20000 = 0.15625 from SingleWiki , but I got 1.328e-36 so the int to void* to float doesn't seem to work in the code below:
#include <cstdio>
int main(){
float flout;
unsigned int num = 1;
int ant;
printf("Int Shift float");
for(unsigned int shift=0;shift<32;shift++){
[Code] ....
View 5 Replies
View Related
Sep 5, 2014
Casting Pointers in C Programming. I don't want to move onto implicit casts until I have this down pat. I'm failing to understand how casting pointers works.
The line
int *mnt = (int*)&flt;
if I read this correctly passes the address of flt which has been converted to an int to the pointer mnt.
1 - When I output mnt I get a garbage value, probably because the address of flt is then converted to a pointer and passed onto mnt as a value and then reinterpreted as a memory address. (that is the first part I don't understand)
2 - - What exactly does the (int*) cast say? Does this mean that a pointer will be returned or an address will be returned. What does the fact that the * is inside the parenthesis mean?
Code:
#include <iostream>
using namespace std;
int main() {
float flt= 6.5;
int *mnt = (int*)&flt;
cout << mnt << endl; // outputs hex memory address
cout << *mnt << endl; // outputs garbage value
}
View 9 Replies
View Related
Feb 26, 2013
I need to send a packet of type byte:
0x00, 0x01, 0x02, 0x11, 0x00, 0x00
to a device via the serial port and then I receive and store data coming from device like this:
0x01, 0x01, 0x01 , 0x00, 0x00, 0x00, 0x01, 0x00, 0x04, 0x01, 0x00.
Writing lines of code through which:
1) I create the array
2) the sending the array to serial port
3) I'll see what I'm sending
4) I get the data
I'm using Visual Studio 2010 and C + + or VC++ language.
View 14 Replies
View Related
