C language, using structs to send data from client to server - c

Question

I have to create a client and server, where the client will send a character and an integer (using structs) and then my client will iterate the letter by n (integer) times and will send it back to the client.
For instance: a and 4 are sent from the client, server will manipulate and send a string of 4 a's (aaaa) back to the client.
I know I am really close to get the code but once I send my char and int, I get a "segmentation fault (core dumped) error". I have done my research and the error shows up due to a missing cast, memory being accessed where is not supposed to access, or that a pointer might be null.
The code is as follow:
Client:
// ClientTest.c
// opens fifo1 for writing and fifo2 for reading
#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>
struct problem {
char letter[1];
int number[1];
};
main (void)
{
struct problem x=0; //Initializing structure to null
int fda; // to write to character server
int fdb; // to read response from character server
int i; // for the iteration
printf("Client: Please enter a character: ");
scanf("%c", &x.letter[0]);
printf("Client: Please enter an integer: ");
scanf("%d", &x.number[0]);
memset(&x.letter, 0, 1);
memset(&x.number, 0, 1);
if((fda=open("FIFO1", O_WRONLY))<0)//opening and validating fifos
printf("cant open fifo to write");
if((fdb=open("FIFO2", O_RDONLY))<0)
printf("cant open fifo to read");
write(fda, x.number, 1);
printf("\nClient: Got the integer sent, now waiting for response ");
//sleep(0.250);
write(fda, x.letter, 1);
printf("\nClient: Got the character sent, now waiting for response ");
char outletter[7];
read(fdb, outletter, 7);
printf("\nClient: received characters from server %c", outletter);
close(fda);
close(fdb);
printf ("\nall done!\n");
}
server
// ServerTest.c
// makes 2 fifos named fifo1 and fifo2
// opens fifo1 for reading and fifo2 for writing
#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>
struct problem {
char letter[1]; // struct to store the character
int number [1]; // struct to store the integer
};
main (void)
{
struct problem x;
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 p;
char outletter[7];
memset(&x.letter, 0, 7);
memset(&x.number, 0, 1);
/* 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, x.letter, 1); //read the character
read(fda, x.number, 1); //read the integer
printf("\nServer: just got character: , %c", x.letter[0]);
printf("\nServer: just got integer: , %d", x.number[0]);
p=x.number[0]-'0';
for( i = 0; i<=p; i++) // iteration to create the character's string
outletter[p] = x.letter[0];
printf("iteration: %d and character: %c\n", i, outletter[0]); // validating the character and integer received
printf("\nServer: outchar is, %s", outletter); // this shows the character to be sent back to client
write(fdb, outletter, p);
printf("\nServer: Got the characters sent: %s", outletter ); // this sends the letter back to client
if(finish == 1)
printf("\nServer: This says I am ready to close ");
close(fda);
close(fdb);
unlink("FIFO1");
unlink("FIFO2");
}

Answer 1

There are many problems with your code, I've made it running but you can still improve it.
Client:
// ClientTest.c
// opens fifo1 for writing and fifo2 for reading
#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>
struct problem {
char letter[1];
int number[1];
};
main (void)
{
struct problem x;
int fda; // to write to character server
int fdb; // to read response from character server
int i; // for the iteration
memset(&x, 0, sizeof(struct problem)) ;
printf("Client: Please enter a character: ");
scanf("%c", x.letter);
printf("Client: Please enter an integer: ");
scanf("%d", x.number);
// removed or else the letter and number would be reverted to zero
// memset(&x.letter, 0, sizeof(char));
// memset(&x.number, 0, sizeof(int));
if((fda=open("FIFO1", O_WRONLY))<0)//opening and validating fifos
printf("cant open fifo to write");
if((fdb=open("FIFO2", O_RDONLY))<0)
printf("cant open fifo to read");
write(fda, x.letter, sizeof(char));
printf("\nClient: Got the character sent, now waiting for response ");
write(fda, x.number, sizeof(int));
printf("\nClient: Got the integer sent, now waiting for response ");
//sleep(0.250);
char outletter[7];
read(fdb, outletter, 7);
printf("\nClient: received characters from server:") ;
printf("%s\n", outletter);
close(fda);
close(fdb);
printf ("\nall done!\n");
}
Server:
// ServerTest.c
// makes 2 fifos named fifo1 and fifo2
// opens fifo1 for reading and fifo2 for writing
#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>
struct problem {
char letter[1]; // struct to store the character
int number[1]; // struct to store the integer
};
main (void)
{
struct problem x;
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 p;
char outletter[7];
memset(x.letter, 0, sizeof(char));
memset(x.number, 0, sizeof(int));
/* 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, x.letter, sizeof(char)); //read the character
read(fda, x.number, sizeof(int)); //read the integer
printf("\nServer: just got character: , %c", x.letter[0]);
printf("\nServer: just got integer: , %d", x.number[0]);
p=x.number[0];
if (p > 6) p = 6; // Cannot write more than 6 characters in outletter
for( i = 0; i<=p; i++) { // iteration to create the character's string
outletter[i] = x.letter[0];
printf("iteration: %d and character: %c\n", i, outletter[i]); // validating the character and integer received
}
outletter[p] = '\0'; // the string must finish with '\0'
printf("\nServer: outchar is, %s", outletter); // this shows the character to be sent back to client
write(fdb, outletter, p);
printf("\nServer: Got the characters sent: %s", outletter ); // this sends the letter back to client
if(finish == 1)
printf("\nServer: This says I am ready to close ");
close(fda);
close(fdb);
unlink("FIFO1");
unlink("FIFO2");
}