fork of C language－逗點大的雨滴

parent process create child process

add value util bigger than five and then exit

#include <unistd.h> /* Symbolic Constants */
#include <sys/types.h> /* Primitive System Data Types */
#include <errno.h> /* Errors */
#include <stdio.h> /* Input/Output */
#include <sys/wait.h> /* Wait for Process Termination */
#include <stdlib.h> /* General Utilities */

int main()
{
   pid_t childpid; /* variable to store the child's pid */
   int value=0; /* 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: Here's my PID: %d\n", getpid());
   while(value<5){
   value+=1;
   printf("Child value= %d\n",value);
   sleep(1);
   }
   printf("Child: Goodbye!\n");
   exit(0);
   }
   else /* fork() returns new pid to the parent process */
   {
   printf("Parenet: Here's my PID: %d\n", getpid());
   while(value<5){
   value+=1;
   printf("Parent value= %d\n",value);
   sleep(1);
   }
   printf("PARENT: Goodbye!\n");
   exit(0); /* parent exits */
   }
   }
   else /* fork returns -1 on failure */
   {
   perror("fork"); /* display error message */
   exit(0);
   }

makefile

fork:fork.o
   cc -o fork fork.o

fork.o:fork.c
   cc -c fork.c

clean:
   rm -rf fork *.o