How to load a string to a structure?

Question

I have a client and a server. I use UDP. (C/Unix)

In server I do have a structure:

typedef struct Header {
int seqid;
int len;
char payload[100];
}
...
char test[100];
struct Header package;
package.seqid = 1;
package.len = 64;
strcpy(package.payload, test);
sendto(sockfd, &package, 100, 0, (struct sockaddr*)&cliaddr, sizeof(cliaddr));

In client I do have the same structure:

struct Header* myrepos;
...
recvfrom(sockfd, recvline, 100, 0, NULL, NULL);
//recvline is a char[100]
...

I want to load into the "myrepos" the submitted structure (submitted by server). How can I do that?

Using a

*angel = (struct Header*)&recvline;

result in compiler errors.

I am not sure if my methid is quite right or it can happen. Are there other solutions?

Thank You!

Answer 1

1: sendto(sockfd, &package, sizeof(struct Header), 0, (struct sockaddr*)&cliaddr, sizeof(cliaddr));

2: recvline = new char [sizeof(struct Header)];

3: myrepos = (struct Header *)recvline;

Answer 2

I guess you are having a couple of problems here.

1. Why are you mentioning the size of the buffer to be sent as 100? It should be sizeof(struct Header) assuming that you want send out 100 bytes of payload always.
2. If you send out integer variables as it is in the network without converting them to 'network order' when you receive and assign them in the other side, you might end up with incorrect values, unless both machines are having the same endianness.

So, my suggestion is that you convert them all into a buffer and send it across and upon receiving decode the buffer to a structure.

Sample way of making a record for sending:

char sbuf[100] = {0};
char test[100] = {"Test Message"};
char *p = sbuf;
int bytestobesent = 0;

p = htonl(1);
p = p+sizeof(long);
p = htonl(64);
p = p+sizeof(long);
memcpy(p, test, strlen(test));

bytestobesent = sizeof(long) + sizeof(long) + strlen(test);

sendto(sockfd, sbuf, bytestobesent , 0, (struct sockaddr*)&cliaddr, sizeof(cliaddr)); 

Just do the reverse of this, when you receive the buffer from the network. Hope this helps.

Answer 3

If you want to send fixed size packages. Then this could be the solution:

Server:

sendto(sockfd, &package, sizeof(package), 0, 
       (struct sockaddr*)&cliaddr, sizeof(cliaddr));

Client:

struct Header myrepos;
...
recvfrom(sockfd, &myrepos, sizeof(myrepos), 0, NULL, NULL);

Of cource you must check return codes of functions.

If you want to send variable sized packages, it would be more complex.