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<concept id="GUID-383C128C-15EB-4C64-9A1F-F1EA826323D0" xml:lang="en"><title>Parent

and Child IPC Using Named Pipes or FIFOs</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>An alternative approach to using the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function

is to use named pipes, or FIFOs. The advantage of using them over the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> mechanism

is that they allow the code in both the parent and child processes to continue

to use file descriptors for communication rather than streams (and avoid modification

to the<codeph> stdin()</codeph>/<codeph>stdout()</codeph> streams of the child

process). </p>

<p>In addition, since each created FIFO is referenced as a file in the file

system, FIFOs allow for more complicated IPC schemes than those offered by

the <xref href="GUID-A9DB6E7C-B8D6-377A-BBE6-39E0A7A09E5D.dita"><apiname>popen()</apiname></xref> function, for example, inter-child process

communication. For more information about the use of FIFOs, see <xref href="http://www.opengroup.org" scope="external">http:\\www.opengroup.org</xref>. </p>

<p><b>Parent process P.I.P.S. example using FIFOs</b></p>

<p>The following code shows how FIFOs can be used in P.I.P.S. by the parent

process.</p>

<codeblock xml:space="preserve">int main(int argc, char *argv[])

{

   char fifoFileName[] = "/root/PortDoc/Example2_c/Symbian/fifofile";

   int fifoResult = mkfifo(fifoFileName,S_IXGRP);

   if(fifoResult == -1)

   {

      //FIFO creation failure.

      printf("\n*** failure mkfifo ***\n");

      return EXIT_FAILURE;

   }

   else

   {

      //FIFO creation successful.

      //Spawn the child process.

      pid_t Childpid;

      char execFileName[] = "/root/PortDoc/Example2_c/Symbian/ChildProg";

      int RetVal= posix_spawn(&Childpid,execFileName,NULL,NULL,NULL,NULL);

      if(RetVal != 0)

      {

         printf("\n*** failure posix_spawn ***\n");

         return EXIT_FAILURE;

      }

      else

      {

         //Open the FIFO. Parent reads from the FIFO

         int ReadFifoFd = open(fifoFileName,O_RDONLY);

         if(ReadFifoFd == -1)

         {

            //Failed to open the Fifo

            printf("\n*** failure Fifo Open ***\n");

            return EXIT_FAILURE;

         }

         else

         {

            //create a receive buffer and clear

            char RxBuffer[100];

            memset(RxBuffer,0,sizeof(RxBuffer));

            //Wait for data from the child process. Child sends a string.

            int nbytes = read(ReadFifoFd,RxBuffer,sizeof(RxBuffer));

            printf("\nMessage Received by Parent=%s",RxBuffer);

            //close the FIFO

            (void)close(ReadFifoFd);

         }

         //wait for the child process to finish      

         (void)waitpid(Childpid,NULL,0);

         //unlink the FIFO

         unlink(fifoFileName);

      }

   }

   return EXIT_SUCCESS;

}

</codeblock>

<p><b>Child process P.I.P.S. example using FIFOs</b></p>

<p>The following code shows how FIFOs can be used in P.I.P.S. by the child

process. </p>

<codeblock xml:space="preserve">int main(int argc, char *argv[])

{

   char fifoFileName[] = "/root/PortDoc/Example2_c/Symbian/fifofile";

   //Open the FIFO. child writes to parent

   int WriteFifoFd = open(fifoFileName,O_WRONLY);

   if(WriteFifoFd == -1)

   {

      //Failed to open the Fifo

      printf("\n*** child failure Fifo Open ***\n");

      return EXIT_FAILURE;

   }

   else

   {

      //create a message to send.

      char TxMsg[] = "Hello Parent\n";

      //Wait for data from the child process. Child sends a string.

      write(WriteFifoFd,TxMsg,sizeof(TxMsg));

      //close the FIFO

     (void)close(WriteFifoFd);

   }

   return EXIT_SUCCESS;

}

</codeblock>

</conbody></concept>