using fork function after getting user's input

Question

How do you get the fork function to work after getting the user's input from the fgets() function and getting tokens from the user's input?

My code:

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

/* the line can have at most 2000 words*/
void tokeniseLine(char *Line, char **Words, int *Wordn);

/* break line into words separated by whitespace, placing them in the
array words, and setting the count to Wordn */

void search&execute();

int main()
{
char Line[4000], *Words[2000], string[4000];
int Stops=0,Wordn=0;
char *end = "exit";

while(1)
{
printf("Enter program: ");
fgets(Line, 4000, stdin ); /* read a line of text here */

/* use of exitting begins when user enters 'exit' or when the program   finally locates/can't locate the user's requested file*/
if ( strcmp(Line, end) == 0 ){
exit(0);
       }
else
if ( strcmp(Line, end) != 0 ) {
printf("file successfully found.");
tokeniseLine(Line,Words,&Wordn);
search&execute();//using fork function to make process
 }
return 0;
 }

 void tokeniseLine(char *Line, char **Words, int *Wordn)
 {
 char *token;

  /* get the first token */
  token = strtok(Line, " \t\n");

  /* walk through other tokens */
  while( token != NULL ) 
  {    
   token = strtok(NULL, " \t\n");
   }
    return;
   }

    void search&execute()//this is the function which I wanted to work last   after the user input is tokenised
   {
    pid_t childpid; /* variable to store the child's pid */
    int retval;     /* child process: user-provided return code */
    int status;     /* parent process: child's exit status */

     /* only 1 int variable is needed because each process would have its
      own instance of the variable
      here, 2 int variables are used for clarity */

     /* now create new process */
      childpid = fork();

      if (childpid >= 0) /* fork succeeded */
     {
      if (childpid == 0) /* fork() returns 0 to the child process */
      {
        printf("CHILD: I am the child process!\n");
        printf("CHILD: Here's my PID: %d\n", getpid());
        printf("CHILD: My parent's PID is: %d\n", getppid());
        printf("CHILD: The value of my copy of childpid is: %d\n",childpid);
        printf("CHILD: Sleeping for 1 second...\n");
        sleep(1); /* sleep for 1 second */
        printf("CHILD: Enter an exit value (0 to 255): ");
        scanf(" %d", &retval);
        printf("CHILD: Goodbye!\n");    
        exit(retval); /* child exits with user-provided return code */
        }
        else /* fork() returns new pid to the parent process */
        {
        printf("PARENT: I am the parent process!\n");
        printf("PARENT: Here's my PID: %d\n", getpid());
        printf("PARENT: The value of my copy of childpid is %d\n",childpid);
        printf("PARENT: I will now wait for my child to exit.\n");
        wait(&status); /* wait for child to exit, and store its status */
        printf("PARENT: Child's exit code is: %d\n", WEXITSTATUS(status));
        printf("PARENT: Goodbye!\n");             
        exit(0);  /* parent exits */       
    }
}
else /* fork returns -1 on failure */
{
    perror("fork"); /* display error message */
    exit(0); 
}

}

I tried to have the fork function to return the fork value, but it doesn't work when I tried to add in user input. How do you fix that?

What do you mean by "have the fork function to return the fork value"? — Some programmer dude, Mar 30 '15 at 08:55
it only compiled up to the point where it printed out: file successfully found. — user4728257, Mar 30 '15 at 11:04
I just want the user input to be tokenised and then get the program go through the fork() function. — user4728257, Mar 30 '15 at 11:06
At least the braces are somehow wrong also one is missing. As well Standard C does not support the `&` characters as part of a symbol name (here: search&execute()`). — alk, Apr 03 '15 at 14:17

score 0 · Answer 1 · answered Aug 15 '15 at 05:41

When the various problems identified in the comments above are fixed, there turn out to be a large number of unused variables, and unused function parameters. Cleaning that up, and ensure printf() formats end with a newline, leads to code like this:

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

void tokeniseLine(char *Line);
void search_execute(void);

int main(void)
{
    char Line[4000];
    char *end = "exit";

    while (1)
    {
        printf("Enter program: ");
        fgets(Line, 4000, stdin );

        if (strcmp(Line, end) == 0)
        {
            exit(0);
        }
        else if (strcmp(Line, end) != 0)
        {
            printf("file successfully found.\n");
            tokeniseLine(Line);
            search_execute();
        }
    }
    return 0;
}

void tokeniseLine(char *Line)
{
    char *token;

    token = strtok(Line, " \t\n");

    while (token != NULL)
    {
        printf("Token: [%s]\n", token);
        token = strtok(NULL, " \t\n");
    }
}

void search_execute(void)
{
    pid_t childpid;
    int retval;
    int status;

    childpid = fork();

    if (childpid >= 0)
    {
        if (childpid == 0)
        {
            printf("CHILD: I am the child process!\n");
            printf("CHILD: Here's my PID: %d\n", getpid());
            printf("CHILD: My parent's PID is: %d\n", getppid());
            printf("CHILD: The value of my copy of childpid is: %d\n", childpid);
            printf("CHILD: Sleeping for 1 second...\n");
            sleep(1);
            printf("CHILD: Enter an exit value (0 to 255): ");
            scanf(" %d", &retval);
            printf("CHILD: Goodbye!\n");
            exit(retval);
        }
        else
        {
            printf("PARENT: I am the parent process!\n");
            printf("PARENT: Here's my PID: %d\n", getpid());
            printf("PARENT: The value of my copy of childpid is %d\n", childpid);
            printf("PARENT: I will now wait for my child to exit.\n");
            wait(&status);
            printf("PARENT: Child's exit code is: %d\n", WEXITSTATUS(status));
            printf("PARENT: Goodbye!\n");
            exit(0);
        }
    }
    else
    {
        perror("fork");
        exit(0);
    }
}

The loop in main() is bogus; the first call to search_execute() has the code exit on all code paths, so the loop in main() never repeats. The else if (strcmp(Line, end) != 0) really doesn't need the if part; if the previous if failed, the code will end up in the block following the else.

Compilation:

The source file was called x19.c:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes \
>     -Wold-style-definition -Werror x19.c -o x19
$

Sample output:

$ ./x19
Enter program: periodic table
file successfully found.
Token: [periodic]
Token: [table]
PARENT: I am the parent process!
PARENT: Here's my PID: 4142
PARENT: The value of my copy of childpid is 4143
PARENT: I will now wait for my child to exit.
CHILD: I am the child process!
CHILD: Here's my PID: 4143
CHILD: My parent's PID is: 4142
CHILD: The value of my copy of childpid is: 0
CHILD: Sleeping for 1 second...
CHILD: Enter an exit value (0 to 255): 47
CHILD: Goodbye!
PARENT: Child's exit code is: 47
PARENT: Goodbye!
$

Basically, the code seems to work more or less sanely, and there wasn't a truly substantive change. There are some improvements that could be made. If there's still a problem, you need to show much more clearly what the issues you see are.

using fork function after getting user's input

1 Answers1