messaging between a parent and child proccess

This is a discussion on messaging between a parent and child proccess within the C++ Programming forums, part of the General Programming Boards category; Code: #include <iostream> #include <unistd.h> #include <sys/types.h> #include <stdlib.h> #include <stdio.h> using namespace std; #define BSIZE 100 void parent(int Msgs); ...

  1. #1
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    messaging between a parent and child proccess

    Code:
    #include <iostream>
    #include <unistd.h>
    #include <sys/types.h>
    #include <stdlib.h>
    #include <stdio.h>
    using namespace std;
    
    #define BSIZE   100
    
    void parent(int Msgs);
    
    
    int main()
    {
            parent(100);
            return 0;
    }
    
    
    void parent(int Msgs)
    {
            int numMsgs = Msgs;
            int pid;
            int x=0;
    
            int pipe1[2];
            int pipe2[2];
            char buf[BSIZE];
            ssize_t  nbytes;
    
            pid = fork();
            if(pid < 0)
                    cout<<"ERROR"<<endl;
    
            else if (pid == 0)
            {
                    close(pipe1[1]);
                    read(pipe1[0], buf, BSIZE);
                    cout<<endl;
                    cout<<"child read"<<endl;
                    close(pipe2[2]);
            }
    
            else
            {
                    close(pipe1[0]);
                    nbytes = write(pipe1[1], "p", 1);
                    cout<<endl;
                    cout<<"parent write"<<endl;
                    close(pipe1[1]);
                    cout<<read(pipe2[0], buf, BSIZE);
                    cout<<endl;
                    cout<<"parent read"<<endl;
                    close(pipe2[0]);
                    //parent code goes here
         }
    
    }

    //the program has to send messages, the problem i am having is that the message doest not get passed from the parent to the child and back and forth. http://www.cs.stevens-tech.edu/~quyn...1/assign1.html is the link for the exact procedures.
    Last edited by v3dant; 09-04-2004 at 12:53 PM.

  2. #2
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  3. #3
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    you have to set up your pipes.

    int err = pipe(pipe1);

  4. #4
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    thansk that worked

  5. #5
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    Code:
    #include <iostream>
    #include <cstring>
    #include <ctime>
    #include <unistd.h>
    #include <sys/types.h>
    #include <stdlib.h>
    #include <stdio.h>
    using namespace std;
    
    #define BSIZE	512
    
    void parent(int Msgs);
    
    
    int main()
    {
    	parent(100);	
    	return 0;
    }
    
    
    void parent(int Msgs)
    {
    	int numMsgs = Msgs;
    	int message = 1;
    	char line [512];
    	int lineNum=0;
    	int pid;
    	int ranLines;
    	int pipe1[2];
    	int pipe2[2];
    	int err1 = pipe(pipe1);
    	int err2 = pipe(pipe2);
    	
    	
    	if(err1 == -1 || err2 == -1)
    		cout<<"error with pipes"<<endl;
    
    	char buf[512];
    	ssize_t  nbytes;
    
    	pid = fork();
    
    	if(pid < 0)
    		cout<<"ERROR"<<endl;
    
    	else if (pid == 0)
    	{
    		int d=0;
    		nbytes=read(pipe1[0], buf, BSIZE);
    		cout<<nbytes<<endl;
    		while((nbytes != -1) && (buf[0] != 'b'))
    		{
    			cout<<"parent: ";
    			cout<<buf[0]<<int(buf[1])<<buf[2]<<buf[3]<<buf[4]<<buf[5];
    			cout<<buf[6]<<buf[7]<<int(buf[8])<<endl;
    			nbytes=read(pipe1[0], buf, BSIZE);
    	
    		}
    			
    	}
    
    	else
    	{	
    		//close(pipe1[0]);
    		srand(time(0));
    		int x=0;
    		int y=0;
    		while(message<2)
    		{
    			ranLines = (1+ rand() % 5);
    			if(message==100)
    				write(pipe1[1],"bye",3);
    			else
    			{
    				for(x=1; x<ranLines+1; x++)
    				{
    					line[0]='m';
    					line[1]=char(message);
    					line[2]=' ';
    					line[3]='l';
    					line[4]='i';
    					line[5]='n';
    					line[6]='e';
    					line[7]=' ';
    					line[8]=char(lineNum+x);
    					y=write(pipe1[1],line,9);			
    				}	  
    			}	
    			message++;
    		}	
    		
    		//close(pipe1[1]);
    		//parent code goes here
    	}
    
    }

    ok now i have the pipes working however i cant make it so that the parent continuoulsy provides random number of messages and the child outputs it. the program just outputs one line and then does not read the next line sent to the child proccess.

  6. #6
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    how abour putting the if/else if/else trio in a loop, say:

    int numMsgs = 0;
    while(numMsgs < Msgs)
    if
    else if
    else
    numMsgs++;
    end while

  7. #7
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    Posts
    26
    Code:
    #include <iostream>
    #include <cstring>
    #include <ctime>
    #include "string2int.h"
    #include <unistd.h>
    #include <sys/types.h>
    #include <stdlib.h>
    #include <stdio.h>
    using namespace std;
    
    #define BSIZE	512
    
    void parent(int Msgs);
    
    
    int main()
    {
    	parent(100);	
    	return 0;
    }
    
    
    void parent(int Msgs)
    {
    	int numMsgs = Msgs;
    	int message = 1;
    	char line [512];
    	int lineNum=0;
    	string linestr;
    	string chldmsg;
    	string msgstr;
    	int pid;
    	int ranLines;
    	int pipe1[2];
    	int pipe2[2];
    	int err1 = pipe(pipe1);
    	int err2 = pipe(pipe2);
    	
    	
    	if(err1 == -1 || err2 == -1)
    		cout<<"error with pipes"<<endl;
    
    	char buf[512];
    	ssize_t  nbytes;
    
    	pid = fork();
    
    	if(pid < 0)
    		cout<<"ERROR"<<endl;
    
    	else if (pid == 0)
    	{
    		int a=0;
    		int chLines;
    		char chMsg[512];
    		string chMsgNum;
    		string lnNum;
    		nbytes=read(pipe1[0], buf, BSIZE);
    		while(nbytes!=0 && buf[0] != 'b')
    		{
    			cout<<"parent: ";
    			for(a=0; buf[a]!= '*'; a++)
    			{
    				cout<<buf[a];
    			}
    			cout<<endl;
    			nbytes=read(pipe1[0], buf, BSIZE);
    			if(nbytes==0)
    			{
    				//child should now send message to parent
    			}
    			
    		}		
    	}
    
    	else
    	{	
    		//close(pipe1[0]);
    		srand(time(0));
    		int x=0;
    		int y=1;
    		int z=0;
    		while(message<101)
    		{
    
    			ranLines = (1+ rand() % 5);
    			if(message==100)
    				write(pipe1[1],"bye",3);
    			else
    			{
    				for(x=1; x<ranLines+1; x++)
    				{
    				
    					y=0;
    					z=0;
    					line[0]='m';
    					msgstr=BasicTypeToStr(message);
    					for(y=1; z<msgstr.size(); y++)
    					{
    						line[y]=msgstr[z];
    						z++;
    					}
    					y=msgstr.size()+1;
    					line[y]=' ';
    					y++;
    					line[y]='l';
    					y++;
    					line[y]='i';
    					y++;
    					line[y]='n';
    					y++;
    					line[y]='e';
    					y++;
    					line[y]=' ';
    					y++;
    					lineNum++;
    					linestr=BasicTypeToStr(lineNum);
    					z=0;
    					for(y; z<linestr.size(); y++)
    					{
    						line[y]=linestr[z];
    						z++;
    					}
    					line[y]='*';
    					cout<<endl;     //write to external file here
    					write(pipe1[1],line,y+1);			
    				}  
    		
    			//parent proccess should now wait for a response from child
    				nbytes=read(pipe2[0],buf,BSIZE);
    				cout<<nbytes<<endl;
    			//	while(nbytes != -1)
    			//	{
    			//		cout<<"parent read"<<endl;
    			//		nbytes=read(pipe2[0],buf,BSIZE);
    
    			//	}
    			}	
    			message++;
    		}	
    		
    		//close(pipe1[1]);
    		//parent code goes here
    	}
    
    }
    i now have it so that the parent sends the #of lines of the message and the child reads it. how can i make it so that the child is able to write a message and have the parent wait for it and read the message from the child and then it writes a message back and so on? For some reason I dont think the read is returning 0 at the end of file.
    Last edited by v3dant; 09-06-2004 at 09:34 AM.

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