Can someone offer me a hand to help me?

Question

1.00/5 (1 vote)

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I am trying to send a 2d char array from server to client,but this doesn't work, it prints me nothing on the client.Im using TCP/IP.Can you help me with some code?

What I have tried:

C++

************SERVER*********

char arr[20][20];

int i,j; 
 for(i=0;i<20;i++){
	for(j=0;j<20;j++){
		send(sock,&arr[i][j],sizeof(char),0);

	}


	}
*******CLIENT***************************

char arr[20][20];


int i,j; 
 for(i=0;i<20;i++){
	for(j=0;j<20;j++){
  		recv(sock,&arr[i][j],sizeof(char),0);
		printf("%s",arr[i][j]);
	}


	}

Posted 11-May-20 8:22am

Member 14825085

Updated 11-May-20 21:52pm

Patrice T

v5

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Comments

Afzaal Ahmad Zeeshan 11-May-20 14:35pm

Sure,

How are you connecting or establishing the connection over TCP/IP? Can you share the entry points for these two programs?

Member 14825085 11-May-20 14:46pm

Its just a typically tcp/ip connection not something special bro

jeron1 11-May-20 15:19pm

So you are successful in establishing a TCP/IP connection?

Member 14825085 11-May-20 17:08pm

Yes i send some simple messages before and works perfectly

jeron1 11-May-20 17:19pm

The return value from the send() function is what you expect?

Member 14825085 11-May-20 17:48pm

Yes i check this

jeron1 11-May-20 18:38pm

Maybe you could try formatting as a char instead of a string, in your
printf statement? (%c instead of %s)

[no name] 11-May-20 14:37pm

Now hard to help, what do you excpect and what do you get?
On a first glance I would say you mix up the indices. You declare i and j but after that you are using in the outer and the inner for both times only i... that cannot come well ;)

Member 14825085 11-May-20 14:45pm

Sorry that was my fault while copying, it is i in the first loop and j in the second. I am expecting the client to print the array which i send from server

[no name] 11-May-20 14:46pm

Then please correct the code in your question using "improve question"

Member 14825085 11-May-20 14:48pm

Okay sorry for this

[no name] 11-May-20 14:49pm

No need to be sorry, simply correct it ;)

RickZeeland 11-May-20 15:01pm

Do you use Windows or Linux ?

[no name] 11-May-20 15:29pm

Why, sorry for the question? But is windows and linux sockets for raw data different?
Thank you very much in advance.

RickZeeland 11-May-20 15:40pm

It's more a question of the included libraries, for Windows you can include Winsock2.h for instance. Needless to say this won't compile for Linux.

Member 14825085 11-May-20 16:55pm

Linux

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RickZeeland · Answer 1 · 2020-05-11T09:49:00

Solution 1

Here is an implementation that can be used both for Windows and Linux:
C sockets portable in windows/linux example · GitHub[^]

sizeof(char)

won't work, you need to pass the length of the string.

Posted 11-May-20 9:49am

RickZeeland

Updated 11-May-20 21:03pm

v2

Comments

Member 14825085 11-May-20 17:13pm

Rickzeeland thx for this but what i have to do when i want to send a 2d char array;

Rick York · Answer 2 · 2020-05-11T13:32:00

There are several different ways to do this. Since you are using C and you have not described the nature of your data at all I will make some assumptions. The primary one is they are going to be variable length strings so I would write the data out with length bytes.

First write the number of rows of data. Use four bytes for this. Then write that number of rows of text data. Just so you don't get too tangled up, I would write an index and a length for each row of text. Use four bytes for the index and two for the length. Then you write the (length) bytes of the string. Continue doing this for every line of data. If you want you could then write an end of array marker. This could be as simple as a few bytes of zeros.

Reading will be just like writing, almost. You have to peel off the bytes of the message and make sure you have more waiting for you. This is one use for the 'peek' option. You could simplify things a bit and first traverse your data and figure out how much you will send and write this as the first four bytes. This would be followed by the row count and then the rows of text. That is a simple operation - number of lines times six plus the length of each line plus four for the initial length and four for the termination.

You could optionally write a terminating null character with each string and if you do then I would have the length bytes include the null. What I mean is if one line has "abc" and you are writing the null too then its length should be four.

As I wrote, this is just one possibility and there are many.

Richard MacCutchan · Answer 3 · 2020-05-11T21:52:00

Your code is somewhat confusing. You do not need to send characters 1 at a time. The main loop should run 20 times, and each time round it can send 20 characters. And the length of your send and receive data should not be sizeof(char) (which is 8) but the count of bytes in the data, which in this case is 1. Also you are trying to print a single character but referring to it as a string. The correct format control for a single character is %c. And unless you know that the 20 characters comprise a null terminate sequence you should never use %s .

Take a look at send(2): send message on socket - Linux man page[^] for more details.

Can someone offer me a hand to help me?

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