I'm a beginner of UNIX. these days I am taking a class about operating system. In lecture materials there is a code below.
#include<stdio.h>
#include<stdlib.h>
#include<sys/wait.h>
#include<sys/types.h>
#include<unistd.h>
int main()
int main()
{
pid_t pid;
//for a child program
pid=fork();
if (pid<0){
fprintf(stderr,"Fork Failed\n");
exit(-1);
}
else if(pid==0){//child process
printf("I am the child %d\n",pid); //not working
execlp("/bin/ls","ls",NULL);
}
else{//parent process
//parent will wait for the child to complete
printf("I am the parent %d\n",pid); //not working
wait(NULL);
printf("Child Complete\n");
exit(0);
}
}
and i expected the result of this program is (file name is fig3-9.c and execute file is a.out)
I am the child 0
a.out concurrent.c fig3-9.c, fig3-11.c
I am the parent (som value)
Child Complete
but real result is below
a.out concurrent.c fig3-9.c, fig3-11.c
Child Complete
I don't know why this program doesn't prinf("I am the child %d\n",pid) and ("I am the parent %d\n")
thanks for your helps
CodePudding user response:
you can run ok as below code.please use getpid() not pid(). man2 getpidenter link description here
#include<stdio.h>
#include<stdlib.h>
#include<wait.h>
#include<sys/types.h>
#include<unistd.h>
int main()
{
pid_t pid;
//for a child program
pid=fork();
if (pid<0){
fprintf(stderr,"Fork Failed\n");
exit(-1);
}
else if(pid==0){//child process
printf("I am the child %d\n",getpid()); //not working
execlp("/bin/ls","ls",NULL);
}
else{//parent process
//parent will wait for the child to complete
printf("I am the parent %d\n",getpid()); //not working
wait(NULL);
printf("Child Complete\n");
exit(0);
}
}
run result: future@ubuntu:~/work/tmp$ ./a.out I am the parent 7383 I am the child 7384 a.out reverse_slist.c seg_ment.c unix_fork_print.c Child Complete