Re: Need some information about fork(2)

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

#define NSTRINGS 5
#define SLEN 255

int
main(int argc, char** argv)
{
char** strings = NULL;
pid_t pid;
int i;

strings = malloc(NSTRINGS * sizeof(char*));
if (!strings)
{
perror("malloc");
exit(errno);
}
for (i = 0; i < NSTRINGS; i++)
{
strings[i] = malloc(SLEN+1);
if (!strings[i])
{
perror("malloc");
exit(errno);
}
}
memccpy(strings[0], "Hello, world!", 0, SLEN);
memccpy(strings[1], "This is an example", 0, SLEN);
memccpy(strings[2], "of a string", 0, SLEN);
memccpy(strings[3], "array holding", 0, SLEN);
memccpy(strings[4], "some strings", 0, SLEN);

pid = fork();
if (pid > 0)
{
/* Parent */
pid_t wpid;
int status;

printf("parent: Waiting for children...\n");
fflush(stdout);
wpid = wait(&status);
if (wpid < 0)
{
perror("wait");
exit(errno);
}
printf("parent: Done waiting for children.\n");
fflush(stdout); /* <-- we don't exit from parent here, */
/* continuing after this if */
}
else if (pid == 0)
{
/* Child */
for (i = 0; i < NSTRINGS; i++)
free(strings[i]);
free(strings);
printf("child: Sleeping for 3 seconds...\n");
fflush(stdout);
sleep(3);
printf("child: Done sleeping.\n");
fflush(stdout);
exit(0); /* <-- we exit from child here, not continuing */
/* the rest of the function main */
}

/* Continued, in parent */
for (i = 0; i < NSTRINGS; i++)
printf("string #%d: \"%s\"\n", i, strings[i]);
for (i = 0; i < NSTRINGS; i++)
free(strings[i]);
free(strings);
return 0;
}
Attached is an example C program using fork(2). It dynamically
allocates a string array with malloc(3), then forks. Child free(3)s the
array, sleep(3)s for 3 seconds, then exits. Parent wait(2)s for
children, then prints the array. The array in the parent is not
affected by free(3) in the child.