socket message sending and receiving problem

hi all~

i made a simple socket test and it worked. but it is weired that the message changes both from client to server and from server to client. for example i send a message "hi" to server and server will get something like "hiU" and if i send this message back to client side i will get a string like "hiU#e" etc, i dont know why and have no idea how to sort it, any help will be grateful, thanks.

here's my code for message sending and receiving.

// client side code

Code:

---

......
// Send input message to server~
int len = write(socketId, message, strlen(message));
if (len < 0)
{
printf("Error: Can not send messages to server~\n");
return -1;
}
printf("Message send to server: %s\n", message);
printf("Message length: %d\n", strlen(message));
// Blocks until client gets a message back~
int msgMaxSize = 128;
char messageBack[msgMaxSize];
len = read(socketId, messageBack, msgMaxSize);
if (len < 0)
{
printf("Error: Can not get message from server~\n");
return -1;
}
printf("Message back from server: %s\n", messageBack);
printf("Message length: %d\n", strlen(messageBack));
......

---

// server side code:

Code:

---

......
// Handle message from the client~
int msgMaxSize = 128;
char message[msgMaxSize];
len = read(clientSocket, message, msgMaxSize);
if (len < 0)
{
printf("Error: Can not read data from client socket~\n");
return -1;
}
printf("Message from client: %s\n", message);
printf("Message length: %d\n", strlen(message));
char messageTo[strlen(message)];
strcpy(messageTo, message);
len = write(clientSocket, messageTo, strlen(messageTo));
if (len < 0)
{
printf("Error: Can not write data to client socket~\n");
return -1;
}
printf("Message to client: %s\n", messageTo);
printf("Message length: %d\n", strlen(messageTo));
......

---

Include room for the null character. Most garbled strings are because you forgot it.


Quzah.

weird. it is not correct even we count null chars. i sent a message "hello" which lengths should be 5(or 6 if a null char considered) but actually server got a string with 7 chars, and if we send those 7 chars back to client which may result in a string of 9 chars. is there any special character appended to the message automatically ?

How are you getting the original message, user input?

Is your message actually "hello" + LF + NULL = 7?

from command line arguments, say if i start server like this:
serversocket.c 12345
it means server may start with local address and listen at port 12345;

and client side may type a command as follows:
clientsocket.c 192.168.1.20 12345 hi
which means client side would like to send a message "hi" to server which address is 192.168.1.20 and listens at port 12345;

and i use several printf to see message sending and receiving details, finally i found there's something wrong with message length, for example:
1. client side sends a "hello" to server;
2. server actually gets a "helloU " (the last char is one could not be displayed which asc code is -86);
3. server send that string back to client;
4. client gets a string like "helloU %" (with two invisible chars in the middle, which asc code are -86 and -65 respectively).

any help ?

When you send the message you are using strlen(msg) rather than strlen(msg) + 1 (to include the terminatingNULL). You use strcpy() to move the message, but the "sender" didn't put a NULL on the end of the message, so the strcpy() will read the "receive" buffer until it finds a NULL (or causes a memory fault). The spurious characters you are reading are garbage from the receive buffer, not actually sent by the "sender". (Which is what quzah was hinting at in #2)