Client-server program

Gday everyone,

I'd like to display recent received messages in the buffer 'msg_cat' when user types in 'display', but it always displays 'No recent messages' after I concatenated messages into 'msg_cat'. I use global buffer 'msg_cat'. Is there something wrong of the way I use 'msg_cat'? Or the affect of using fork function in main?

I spent so much time on time, but I really don't know how to fix this problem.

It really depends on you guys experts here. Please help me out if you're interested in this.

I'd appreciate it.

Code:

char msg_cat[1000];	

//Receive, store and display recent messages when user type 'display'.
void displayMulticastedMessage(int condition){
	char *msg;	
	int stop = -1;	
      

        //Display recent multicast messages.
	if (condition == 2){
		if (strcmp(msg_cat, "") != 0){
			printf("msg_cat: %s", msg_cat);
			strcpy(msg_cat, "");
		}
		else{
			printf("No recent messages\n");
		}
	}

	while(stop < 0){
		//Receive multicasted messages from server and store in msg buffer.
		msg = (char *)recvfromDST (&read_EP, sockMulti);	

		//Concatenate message msg into buffer msg_cat.
		strcat(msg_cat, msg);
		strcat(msg_cat, "\n");					
	
		//Display a receiving multicast message to user
		if (msg != NULL){
			printf("----- Waiting for Multicasted message ----- \n");
			printf("\nReceived multicast message ==> %s \n", msg);
		}
		else{
			stop = 0;
		}			
	}
}



void receiveUserMessage(int sock){		
	int stop = -1;
	char *msg;	

	while (stop < 0){
		printf("Type message or 'display' to display recent multicasted messages or	'end' to quit \n");	
		
		//Read msg from user
	  		scanf ("%s", KB_buff);		
		//Display recent multicast messages.
		if (strncmp(KB_buff, "display", 7) == 0){	
			int display = 2;
			displayMulticastedMessage(display);
		}	
		
		//Check message format and send message if it is correct.
		else{			
				int stop = sentMessage(KB_buff,sock);			
		}		
		printf("\n");
	}
}



int main(){

if (pid == 0) // i am the child process
		{
			
			//Receive user input and commands
			receiveUserMessage(MC_socket);
		}
		else 
		{
			if (pid < 0) // ERROR !
			{
				perror("fork");
				exit(1);
			}
			else // parent process
			{				
				int user = -1;
				displayMulticastedMessage(user);	
						
			}
		}
}

Have you tried debugging it?

Where are you calling fork()?

I didn't put the code for declaration of fork to make it easy to read.Sorry

Ofcourse I tried to run it for ages. I tried to print out the buffer 'msg_cat', then it works.
But when I call it from function 'receiveUserMessage', then it prints nothing.

Here is the code.

Code:

char msg_cat[1000];	

//Receive, store and display recent messages when user type 'display'.
void displayMulticastedMessage(int condition){
	char *msg;	
	int stop = -1;	
      

        //Display recent multicast messages.
	if (condition == 2){
		if (strcmp(msg_cat, "") != 0){
			printf("msg_cat: %s", msg_cat);
			strcpy(msg_cat, "");
		}
		else{
			printf("No recent messages\n");
		}
	}

	while(stop < 0){
		//Receive multicasted messages from server and store in msg buffer.
		msg = (char *)recvfromDST (&read_EP, sockMulti);	

		//Concatenate message msg into buffer msg_cat.
		strcat(msg_cat, msg);
		strcat(msg_cat, "\n");					
	
		//Display a receiving multicast message to user
		if (msg != NULL){
			printf("----- Waiting for Multicasted message ----- \n");
			printf("\nReceived multicast message ==> %s \n", msg);
		}
		else{
			stop = 0;
		}			
	}
}



void receiveUserMessage(int sock){		
	int stop = -1;
	char *msg;	

	while (stop < 0){
		printf("Type message or 'display' to display recent multicasted messages or	'end' to quit \n");	
		
		//Read msg from user
	  		scanf ("%s", KB_buff);		
		//Display recent multicast messages.
		if (strncmp(KB_buff, "display", 7) == 0){	
			int display = 2;
			displayMulticastedMessage(display);
		}	
		
		//Check message format and send message if it is correct.
		else{			
				int stop = sentMessage(KB_buff,sock);			
		}		
		printf("\n");
	}
}



int main(){

                int pid;
		pid = fork();


if (pid == 0) // i am the child process
		{
			
			//Receive user input and commands
			receiveUserMessage(MC_socket);
		}
		else 
		{
			if (pid < 0) // ERROR !
			{
				perror("fork");
				exit(1);
			}
			else // parent process
			{				
				int user = -1;
				displayMulticastedMessage(user);	
						
			}
		}
}