Can not get valid value from Char* buffer

This is a discussion on Can not get valid value from Char* buffer within the C Programming forums, part of the General Programming Boards category; Hi,guys: I put two struct variables into a continuous memory at first by using memcpy(). And then I want to ...

  1. #1
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    Can not get valid value from Char* buffer

    Hi,guys:

    I put two struct variables into a continuous memory at first by using memcpy(). And then I want to print out each variable's element. Sometimes it works,but sometimes it just prints out "0". Can someone tell me the reason of that?


    Thanks,
    Attached Files Attached Files
    • File Type: c test.c (711 Bytes, 45 views)

  2. #2
    - - - - - - - - oogabooga's Avatar
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    The only thing I see wrong is an egregious lack of spacing. BTW, sizeof(char) is defined as 1.

  3. #3
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    post your code.

  4. #4
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    Works all the time for me. What do you mean it works sometimes?

  5. #5
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    The issue happens in the MPI code. The new code is attached.
    Code:
    #include <stdio.h>
    #include <mpi.h>
    #include <stdlib.h>
    #include <string.h>
    typedef struct message message;
    struct message
    {
      message*prev;
    	message*next;
    	int recv_pe;
    };
    
    //typedef struct message message;
    
    int main (int argc, char **argv)
    {
      int rank, size;
     
      int iter=1000;
      int number=15;
    	
    	int ierr,errclass;
      ierr=0; 
    	MPI_Request request;
    	MPI_Status status; 
    	int send_buffer[5],recv_buffer[5];
      MPI_Init (&argc, &argv);	/* starts MPI */
      MPI_Comm_rank (MPI_COMM_WORLD, &rank);	/* get current process id */
      MPI_Comm_size (MPI_COMM_WORLD, &size);	/* get number of processes */
     
    // MPI_Errhandler_set(MPI_COMM_WORLD,MPI_ERRORS_RETURN); /* return info about
    //	      errors */
    //	printf( "Hello world from process %d of %d\n", rank, size );
    	if(rank==0)
    	{  
    	    int kk;
    	    for(kk=0;kk<iter;kk++)
    				{
    	    int buffsize= number*sizeof(message);
    			char*buffer=(char*)malloc(buffsize*sizeof(char));
    	   // void*buffer=(char*)malloc((unsigned)buffsize);
    			int position=0;
    			message* sendevent[number];
    			int i;
    			for(i=0,position=0;i<number;i++,position+=sizeof(message))
    			{
    				sendevent[i]=malloc(sizeof(message));
    				sendevent[i]->recv_pe=i;
            memcpy(&buffer[position],sendevent[i],sizeof(message));
          }
    			ierr= MPI_Isend(buffer,buffsize, MPI_BYTE,1, 1,MPI_COMM_WORLD,&request);         
    			}
    		}
    	else
    		{
    		  int kk;
    			for(kk=0;kk<iter;kk++)
    			{
    	    int buffsize=number*sizeof(message);
    			char*buffer=(char*)malloc(sizeof(char)*buffsize);
    				int position=0;
    			  message *tmp=NULL;
    				int flag=0;
    				int i;
    				MPI_Request request;
    				while(flag==0)
    					{
    						MPI_Iprobe(MPI_ANY_SOURCE,
    						MPI_ANY_TAG,
    						 MPI_COMM_WORLD,
    						 &flag,
    						 &status);
              }
             ierr=MPI_Irecv(buffer,buffsize,MPI_BYTE,0,1,MPI_COMM_WORLD,&request);   		        
    				for(i=0,position=0;i<number;i++,position+=sizeof(message))
    				{
    				// MPI_Unpack(buffer,buffsize,&position,&revevent[i],sizeof(revevent[i]),MPI_BYTE,MPI_COMM_WORLD);
    				 tmp=(message*)&buffer[position];
    				 if(i==1&&tmp->recv_pe==0)
    				 printf("error :recv data invalid\n");
    				}
    			}
    		}
    				
      MPI_Finalize();
      return 0;
    }
    Attached Files Attached Files
    Last edited by Salem; 01-05-2012 at 02:54 PM. Reason: inlined code - indent it crap due to mixed spaces and tabs

  6. #6
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    Post your code means cut and paste it into the edit window when you make a post. Don't attach it as a file, it's a PITA for us. Attachments are more suited for images and the like, non-text files. Be sure to use code tags. Read this link: Announcements - General Programming Boards.

  7. #7
    and the hat of int overfl Salem's Avatar
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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