Unable to process the pipe function - c

Question

Unable to process the pipe function where a give pipes in which one process sends a string message to a second process, and the second process reverses the case of each character in the message and sends it back to the first process.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <stdbool.h>
// Parent: reads from P1_READ, writes on P1_WRITE
// Child: reads from P2_READ, writes on P2_WRITE
#define P1_READ 0
#define P2_WRITE 1
#define P2_READ 2
#define P1_WRITE 3
// the total number of pipe *pairs* we need
#define NUM_PIPES 2
/*
toggleString accepts an a pointer to char array, allocates size for the
string to be toggled,
copys the argument into a string, loops through the string and for every
uppercase character
we set it to its lower case counterpart and vice versa, returning the
toggled string
*/
char *toggleString(char *argv){
int i; /* Declare counter */
char *str = malloc(sizeof(argv[1])); /* Declare array sizeof input */
strcpy(str, argv); /* Copy String to char array */
for(i=0;str[i]!='\0';i++) { //Loop through length of string
if(str[i]>='A'&&str[i]<='Z'){ //if the array at i is uppercase
str[i]+=32; //Make it lower case
} else if (str[i]>='a'&&str[i]<='z') {// if the array at i is lowercase
str[i]-=32; //Make it uppercase
}
}
return str;
}
/*
int inputValidation accept and integer (number of arugments) and a
pointer to the cmd line input array
We check to see if the command line input contains the minimal number of
arugments and check to see
whether or not the user input contains at least one reversible haracter,
if all goes well we return 0
*/
int inputValidation(int argc, char *argv[]){
int i; //Declare counter variable
bool c = false; //Declare boolean flag using imported <stdbool.h>
char str[strlen(argv[1])]; //Declare str
strcpy(str, argv[1]); //copy argument into str
if (argc != 2) { // check to see if we have enough arguments to
continue
// Prompt user of correct usage
fprintf(stderr, "\nUsage: %s <string> or <'string 1, string 2', ...,
string n'> for multiple strings\n", argv[0]);
exit(EXIT_FAILURE); //Exit on improper input
} else {
//loop through our string
for(i=0;i<strlen(str);i++) {
//if any any char is a reversible character
if(isalpha((int) str[i])){
c = true; //set the flag to true
}
}
if(c == false){ //If flag is false input does not contain any
reversible charachters
printf("\nSorry, The string you entered did NOT contain any
Alphabetical Characters\nRun me again, with at least 1 Alphabetical
character\n\n");
exit(EXIT_FAILURE); //Exit on improper input
}
return (0);
}
}
/*
Main takes input from command line, calls input validation to make sure of
proper input,
then creates the pipes we will need and the forks the child process, Parent
and Child
execute they're respective code
*/
int main(int argc, char *argv[]) {
assert(argc>1);
int fd[2*NUM_PIPES]; //Declare int[] of file descriptors
int len, i; //Declare length and integer for count
pid_t pid; //Declare process id
char parent[strlen(argv[1])]; //Declare Parent array
char child[strlen(argv[1])]; //Declare Child array
if(inputValidation(argc, argv) == 0) /* Check for proper input */
strcpy(parent, argv[1]);
// create all the descriptor pairs we need
for (i=0; i<NUM_PIPES; ++i)
{
if (pipe(fd+(i*2)) < 0)
{
perror("Failed to allocate pipes");
exit(EXIT_FAILURE);
}
}
// fork() returns 0 for child process, child-pid for parent process.
if ((pid = fork()) < 0)
{
perror("Failed to fork process");
return EXIT_FAILURE;
}
//////////////////////////////Childs Code
BEGINS//////////////////////////////////
// if the pid is zero, this is the child process
if (pid == 0)
{
// Child. Start by closing descriptors we
// don't need in this process
close(fd[P1_READ]);
close(fd[P1_WRITE]);
// used for output
pid = getpid();
// wait for parent to send us a value
len = read(fd[P2_READ], &child, len);
if (len < 0)
{
perror("Child: Failed to read data from pipe");
exit(EXIT_FAILURE);
}
else if (len == 0)
{
// not an error, but certainly unexpected
fprintf(stderr, "Child: Read EOF from pipe");
}
else
{
// report pid to console
printf("Child(%d): Recieved Message\n\nChild(%d): Toggling Case and
Sending to Parent\n",pid, pid);
// send the message to toggleString and write it to pipe//
if (write(fd[P2_WRITE], toggleString(child), strlen(child)) < 0)
{
perror("Child: Failed to write response value");
exit(EXIT_FAILURE);
}
}
// finished. close remaining descriptors.
close(fd[P2_READ]);
close(fd[P2_WRITE]);
return EXIT_SUCCESS;
}
//child code ends///
//////////////////////////////Parent Code
BEGINS//////////////////////////////////
// Parent. close unneeded descriptors
close(fd[P2_READ]);
close(fd[P2_WRITE]);
// used for output
pid = getpid();
// send a value to the child
printf("\nParent(%d): Sending %s to Child\n\n", pid, argv[1]);
if (write(fd[P1_WRITE], argv[1], strlen(argv[1])) != strlen(argv[1]))
{
perror("Parent: Failed to send value to child ");
exit(EXIT_FAILURE);
}
// now wait for a response
len = read(fd[P1_READ], &parent, strlen(parent));
if (len < 0)
{
perror("Parent: failed to read value from pipe");
exit(EXIT_FAILURE);
}
else if (len == 0)
{
// not an error, but certainly unexpected
fprintf(stderr, "Parent(%d): Read EOF from pipe", pid);
}
else
{
// report what we received
printf("\nParent(%d): Received %s from Child\n\n", pid, parent);
}
// close down remaining descriptors
close(fd[P1_READ]);
close(fd[P1_WRITE]);
// wait for child termination
wait(NULL);
return EXIT_SUCCESS;
}
//////////////////////////////Parent Code
ENDS//////////////////////////////////

Answer 1

This works:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include <stdbool.h>
#define P1_READ 0
#define P2_WRITE 1
#define P2_READ 2
#define P1_WRITE 3
#define NUM_PIPES 2
static
char *toggleString(char *argv)
{
int i;
char *str = malloc(strlen(argv) + 1); /* Key Fix */
strcpy(str, argv);
for (i = 0; str[i] != '\0'; i++)
{
if (str[i] >= 'A' && str[i] <= 'Z')
{
str[i] += 32;
}
else if (str[i] >= 'a' && str[i] <= 'z')
{
str[i] -= 32;
}
}
return str;
}
static
int inputValidation(int argc, char *argv[])
{
bool c = false;
char str[strlen(argv[1])];
strcpy(str, argv[1]);
if (argc != 2)
{
fprintf(stderr, "\nUsage: %s <string> or <'string 1, string 2', ..., string n'> for multiple strings\n", argv[0]);
exit(EXIT_FAILURE);
}
else
{
for (size_t i = 0; i < strlen(str); i++)
{
if (isalpha((int)str[i]))
{
c = true;
}
}
if (c == false)
{
printf("\nSorry, The string you entered did NOT contain any"
" Alphabetical Characters\nRun me again, with at least 1 Alphabetical"
" character\n\n");
exit(EXIT_FAILURE);
}
return(0);
}
}
int main(int argc, char *argv[])
{
assert(argc > 1);
int fd[2 * NUM_PIPES];
int len, i;
pid_t pid;
char parent[strlen(argv[1])];
char child[strlen(argv[1])];
if (inputValidation(argc, argv) == 0)
strcpy(parent, argv[1]);
for (i = 0; i < NUM_PIPES; ++i)
{
if (pipe(fd + (i * 2)) < 0)
{
perror("Failed to allocate pipes");
exit(EXIT_FAILURE);
}
}
if ((pid = fork()) < 0)
{
perror("Failed to fork process");
exit(EXIT_FAILURE);
}
if (pid == 0)
{
close(fd[P1_READ]);
close(fd[P1_WRITE]);
pid = getpid();
len = read(fd[P2_READ], child, sizeof(child));
if (len < 0)
{
perror("Child: Failed to read data from pipe");
exit(EXIT_FAILURE);
}
else if (len == 0)
{
fprintf(stderr, "Child: Read EOF from pipe\n");
}
else
{
child[len] = '\0';
printf("Child(%d): Received Message [%s]\nChild(%d): Toggling Case and Sending to Parent\n", pid, child, pid);
char *toggled = toggleString(child);
printf("Child(%d): Sending [%s]\n", pid, toggled);
if (write(fd[P2_WRITE], toggled, len) < 0)
{
perror("Child: Failed to write response value");
exit(EXIT_FAILURE);
}
free(toggled);
}
close(fd[P2_READ]);
close(fd[P2_WRITE]);
return EXIT_SUCCESS;
}
close(fd[P2_READ]);
close(fd[P2_WRITE]);
pid = getpid();
printf("\nParent(%d): Sending [%s] to Child\n\n", pid, argv[1]);
len = strlen(argv[1]);
if (write(fd[P1_WRITE], argv[1], len) != len)
{
perror("Parent: Failed to send value to child");
exit(EXIT_FAILURE);
}
len = read(fd[P1_READ], parent, sizeof(parent));
if (len < 0)
{
perror("Parent: failed to read value from pipe");
exit(EXIT_FAILURE);
}
else if (len == 0)
{
fprintf(stderr, "Parent(%d): Read EOF from pipe\n", pid);
}
else
{
parent[len] = '\0';
printf("\nParent(%d): Received [%s] from Child\n\n", pid, parent);
}
close(fd[P1_READ]);
close(fd[P1_WRITE]);
wait(NULL);
return EXIT_SUCCESS;
}
It was painful extracting your code from your comments, and the split over multiple line strings, and so on. The toggleString() function was broken — allocating 1 byte and then copying a string over that. The other code was not careful about null-terminating strings and handling them. These are basically the problems diagnosed in the comments.
Sample run:
$ pp53 'AbSoLuTeLy GlOrIoUs'
Parent(5209): Sending [AbSoLuTeLy GlOrIoUs] to Child
Child(5210): Received Message [AbSoLuTeLy GlOrIoUs]
Child(5210): Toggling Case and Sending to Parent
Child(5210): Sending [aBsOlUtElY gLoRiOuS]
Parent(5209): Received [aBsOlUtElY gLoRiOuS] from Child
$