why the wait() function takes more argument?

i tried with the waitpid() function, it takes three argument, while i implement a below code , i had a some mistakes, instead of waitpid() function i use the wait() function with the three argument. it work properly i don't how its working. Any one can explain it??

 #include<stdio.h>
  #include<stdlib.h>
 #include<unistd.h>

main()
 {
    pid_t pid;
    int p;

    if((pid=fork())==0){
            printf("Child present\n");
            sleep(2);
            printf("Child terminated\n");
            _exit(0);
    }
    wait(pid,&p,0);                                                                                         
    printf("parent terminated\n");
    return 0;
 }

But the syntax for the wait function is

 pid_t wait(int *status);

Solution

As per the man page here, you need to include <sys/types.h> and <sys/wait.h> header files to use wait() [or waitpid()] which I am not seeing in your code.

It is very much likely that your compiler used some implicit declaration of wait() function, which, in case,

accept any number of input argument
return an integer.

If you include the aforesaid header files and complie, your compiler should produce the warning regarding

too many arguments to function "wait"