fork child and parent processes

Question

I am trying to create a program that uses fork   to create a new process  The sample output should look like so   This is the child process  My pid is 733 and my parent s id is 772  This is the parent process  My pid is 772 and my child s id is 773   This is how I coded my program    include  lt stdio h gt   include  lt stdlib h gt   int main         printf  This is the child process  My pid is  d and my parent s id is  d  n   getpid    fork          return 0      This results in the output   This is the child process  My pid is 22163 and my parent s id is 0  This is the child process  My pid is 22162 and my parent s id is 22163   Why is it printing the statement twice and how can I get it to properly show the parent s id after the child id displays in the first sentence   EDIT    include  lt stdio h gt   include  lt stdlib h gt   int main     int pid   fork     if  pid    0        printf  This is the child process  My pid is  d and my parent s id is  d  n   getpid    getppid       else       printf  This is the parent process  My pid is  d and my parent s id is  d  n   getpid    pid      return 0

User · Answer

It is printing twice because you are calling printf twice  once in the execution of your program and once in the fork   Try taking your fork   out of the printf call

User · Answer

Start by reading the fork man page as well as the getppid   getpid man pages   From fork s     On success  the PID of the child process is returned in the parent s   thread of execution  and a 0 is returned in the child s thread of   execution  On failure  a -1 will be returned in the parent s context    no child process will be created  and errno will be set appropriately    So this should be something down the lines of  if   pid fork     0       printf  yada yada  u and yada yada  u  getpid   getppid       else     avoids error checking       printf  Dont yada yada me  im your parent with pid  u    getpid         As to your question      This is the child process  My pid is 22163 and my parent s id is 0       This is the child process  My pid is 22162 and my parent s id is   22163    fork   executes before the printf  So when its done  you have two processes with the same instructions to execute  Therefore  printf will execute twice  The call to fork   will return 0 to the child process  and the pid of the child process to the parent process   You get two running processes  each one  will execute this instruction statement   printf       My pid is  d and my parent s id is  d  getpid   0      and  printf       My pid is  d and my parent s id is  d  getpid   22163                                                                                                       To wrap it up  the above line is the child  specifying its pid  The second line is the parent process  specifying its id  22162  and its child s  22163

User · Answer

This is the correct way for getting the correct output     However  childs parent id maybe sometimes printed as 1 because parent process gets terminated and the root process with pid   1 controls this orphan process    pid t  pid   pid   fork     if  pid    0       printf  This is the child process  My pid is  d and my parent s id        is  d  n   getpid    getppid      else       printf  This is the parent process  My pid is  d and my parent s           id is  d  n   getpid    pid

User · Answer

We control fork   process call by if  else statement  See my code below   int main        int forkresult  parent ID      forkresult fork       if forkresult   0                printf   I am the parent my ID is    d    getpid             printf   and my child ID is    d n    forkresult           parent ID   getpid        if forkresult   0        printf   I am the  child ID is    d  getpid        else       printf   and my parent ID is    d   parent ID

User · Answer

It is printing the statement twice because it is printing it for both the parent and the child   The parent has a parent id of 0  Try something like this    pid t  pid   pid   fork     if  pid    0       printf  This is the child process  My pid is  d and my parent s id is  d  n   getpid   getppid      else      printf  This is the parent process  My pid is  d and my parent s id is  d  n   getpid    getppid

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