c language memory management with string segments and fifos

Question

Good evening, I need to create a program that will ask for 3 segment names, each segment will ask for a value. my total memory is 2000 units. I need to use structs and fifos to communicate between a client (which will get the input from the user) and a server (which will process the total units). the client will send back the beginning and ending addresses for each segment, as well as any leftover memory.

my issue once I run is that I'm getting a segmentation fault. I can't really see where I might be overwriting the memory or if I'm resetting the memory at some point. any observations or suggestions are welcome, thanks.

client code:

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>


// creating the struct for the program
struct probsiz{
   int seg1 [1]; //segment 1 size
   int seg2 [1]; //segment 2 size
   int seg3 [1]; //segment 3 size
   int segsum [7]; //sum for all the segments
   int leftov [1]; //memory leftovers

} ;

struct probseg {     

   char segment[64]; //segments
};


main (void)
{
  struct probsiz numbs; //defining the structures
  struct probseg names; 

  int fda;  // to write to character server
  int fdb;  // to read response from character server

  //setting up the memory

  memset(numbs.seg1, 0, sizeof(struct probsiz)); //setting up memory for the first segment
  memset(numbs.seg2, 0, sizeof(struct probsiz)); //setting up memory for the second segment
  memset(numbs.seg3, 0, sizeof(struct probsiz)); //setting up memory for the third segment
  memset(numbs.segsum, 0, sizeof(struct probsiz));// setting up memory for the sum of all segments
  memset(numbs.leftov, 0, sizeof(struct probsiz)); //setting up memory for the first segment
  memset(names.segment, 0, sizeof (struct probseg));// setting up memory for the segments




  //reading the requested memory and segment name from the user
  printf("Client: Please enter requested memory 1: ");
  scanf("%d", &numbs.seg1[0]);
  while (numbs.seg1 <=0){
      printf("Client: please enter a valid request: ");
      scanf("%d", &numbs.seg1[0]);
  }
  printf("Client: Please enter segment 1 name: ");
  scanf("%s", names.segment[0]);


  printf("Client: Please enter requested memory 2: ");
  scanf("%d", &numbs.seg2[0]);
  while (numbs.seg1 <=0){
      printf("Client: please enter a valid request: ");
      scanf("%d", &numbs.seg2[0]);
  }
  printf("Client: Please enter segment 2 name: ");
  scanf("%s", names.segment[1]);


  printf("Client: Please enter requested memory 3: ");
  scanf("%d", &numbs.seg3[0]);
  while (numbs.seg3 <=0){
      printf("Client: please enter a valid request: ");
      scanf("%d", &numbs.seg3[0]);
  }
  printf("Client: Please enter segment 3 name: ");
  scanf("%s", names.segment[2]);

  //send and write into the fifos

  printf("\nClient: Got the sizes sent now waiting for server's response\n");

 write(fda, &numbs, sizeof(struct probsiz));
 write(fda, &names, sizeof(struct probseg));


  //read from the fifos
 read(fdb, &numbs, sizeof(struct probsiz));

 if (numbs.leftov[0] >=0) {

     printf("\nClient: address for segment 1 is: %d - %d", numbs.segsum[0], numbs.segsum[1]);
     printf("\nClient: address for segment 2 is: %d - %d", numbs.segsum[2], numbs.segsum[3]);
     printf("\nClient: address for segment 3 is: %d - %d", numbs.segsum[4], numbs.segsum[5]);
     printf("\nClient: leftover memory is: %d", numbs.leftov[0]);
     printf("\nall done!");
 }
 else
 {
     printf("\nClient: segment size is over the capacity, please try again");
     printf("\nall done!\n");

 }

  //this closes the fifos
  close(fda);
  close(fdb);


  printf ("\nall done!\n");

}

server code:

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>



// creating the struct for the program
struct probsiz{
   int seg1 [1]; //segment 1 size
   int seg2 [1]; //segment 2 size
   int seg3 [1]; //segment 3 size
   int segsum [1]; //sum for all the segments
   int leftov [1]; //memory leftovers

} ;

struct probseg {     

   char segment[64]; //for the segments
};

main (void)
{
  struct probsiz numbs; //  structure definitions
  struct probseg names;


  int fda;  // to read from client char
  int fdb;  // to write to client char
  int finish;   // lets me know that client is done
  int i;    // because C needs this defined as int
  int m=2000; //total memory units
  int mtot;  //memory total from the sum of all the segments

  //setting up the memory 

  memset(numbs.seg1, 0, sizeof(struct probsiz)); //setting up memory for the first segment
  memset(numbs.seg2, 0, sizeof(struct probsiz)); //setting up memory for the second segment
  memset(numbs.seg3, 0, sizeof(struct probsiz)); //setting up memory for the third segment
  memset(numbs.segsum, 0, sizeof(struct probsiz));// setting up memory for the sum of all segments
  memset(numbs.leftov, 0, sizeof(struct probsiz)); //setting up memory for the first segment
  memset(names.segment, 0, sizeof (struct probseg));// setting up memory for the segments


  /* Create the fifos and open them  */
  if ((mkfifo("FIFO1",0666)<0 && errno != EEXIST))
    {
    perror("cant create FIFO1");
    exit(-1);
    }
  if ((mkfifo("FIFO2",0666)<0 && errno != EEXIST))
    {
    perror("cant create FIFO2");
    exit(-1);
    }
  if((fda=open("FIFO1", O_RDONLY))<0)
     printf("cant open fifo to write");
  if((fdb=open("FIFO2", O_WRONLY))<0)
     printf("cant open fifo to read");

  read(fda, &numbs, sizeof(struct probsiz)); //read the sizes
  read(fda, &names, sizeof(struct probseg)); //read the segments

  //printing out the characters on the server side to validate the data in

  strcpy(names.segment, names.segment);
  mtot=numbs.seg1[0]+numbs.seg2[0]+numbs.seg3[0];
  numbs.leftov[0]=m-mtot;

  printf("Server: just got segment 1: %s", names.segment[0]);
  printf("Server: just got segment 1 size: %d", numbs.seg1[0]);

  printf("Server: just got segment 2: %s", names.segment[0]);
  printf("Server: just got segment 2 size: %d", numbs.seg2[0]);

  printf("Server: just got segment 3: %s", names.segment[0]);
  printf("Server: just got segment 3 size: %d", numbs.seg3[0]);


  //calculation of memory addresses
  numbs.segsum[0]=0;
  numbs.segsum[1]= numbs.seg1[0]-1;
  numbs.segsum[2]= numbs.seg1[0];
  numbs.segsum[3]= numbs.segsum[2]+numbs.seg2[0]-1;
  numbs.segsum[4]= numbs.segsum[3]+1;
  numbs.segsum[5]= numbs.segsum[4]+numbs.seg3[0];
  numbs.segsum[6]=0;


  write(fdb, &numbs, sizeof(struct probsiz));

  if (numbs.leftov[0] >=0) {

     printf("\nClient: address for segment 1 is: %d - %d", numbs.segsum[0], numbs.segsum[1]);
     printf("\nClient: address for segment 2 is: %d - %d", numbs.segsum[2], numbs.segsum[3]);
     printf("\nClient: address for segment 3 is: %d - %d", numbs.segsum[4], numbs.segsum[5]);
     printf("\nClient: leftover memory is: %d", numbs.leftov[0]);
     printf("\nall done!");
 }
 else
 {
     printf("\nClient: segment size is over the capacity, please try again");
     printf("\nall done!\n");

 }

  if(finish == 1)
    printf("\nServer: This says I am ready to close ");
  close(fda);
  close(fdb);
  unlink("FIFO1");
  unlink("FIFO2");
}

Compile with symbols (using option `-g` for GCC) and then run the program using a debugger (for example GBD (`gdb`)). After the it crashed do a `bt ` and find the line of code that made the program crash along with its call stack. — alk, Sep 23 '16 at 06:28
the client is crashing and the server does not get any data :( — mr_nyo, Sep 23 '16 at 14:39
finally made the client work, however the server is not receiving any data, could be that my fifos are not working properly? — mr_nyo, Sep 23 '16 at 17:42

score 0 · Accepted Answer · answered Sep 23 '16 at 06:44

0

Not sure it is the only issue, but your memset is probably causing the segmentation fault.

You have defined:

struct probsiz{
   int seg1 [1]; //segment 1 size               size = sizeof(int)
   int seg2 [1]; //segment 2 size               size = sizeof(int)
   int seg3 [1]; //segment 3 size               size = sizeof(int)
   int segsum [7]; //sum for all the segments   size = sizeof(int*7)
   int leftov [1]; //memory leftovers           size = sizeof(int)

} ;

total size of probsiz is sizeof(int * 11)

Now lets look at this line for example:

memset(numbs.leftov, 0, sizeof(struct probsiz)); //setting up memory for the first segment

You are telling the computer to fill 0's starting at numbs.leftov to the length of the entire struct.

Hope I helped

answered Sep 23 '16 at 06:44

Shay Gold

403
4
14

I'll try to work on it this morning, I was really tired last night, thanks for the suggestions I'll work on it right now – mr_nyo Sep 23 '16 at 14:40
well I changed the memsets from sizeof statements to the actual number on the structs, and I still got the segmentation fault, could it be something with the fact that I'm getting the segmentation names written on the previous one? – mr_nyo Sep 23 '16 at 15:09
finally made the client work, however the server is not receiving any data, could be that my fifos are not working properly – mr_nyo Sep 23 '16 at 17:42
1. You read the names to names.segment[0], names.segment[1] and names.segment[2], which is fine if you only plan a name to be 1 char long. Otherwise you should allocate names.seg1[SIZE], names.seg2[SIZE] and names.seg3[SIZE] 2. you do not check return values! if you did, you whould have noticed you never opened fba and fdb... – Shay Gold Sep 25 '16 at 05:40
ok I'll fix it for my next project, because I need to use that same program again for the client. Thanks for the suggestions :) – mr_nyo Sep 27 '16 at 02:26

c language memory management with string segments and fifos

1 Answers1