c - Retrieving return code from child process using wait()? -

i have 2 files "prime.c" , "singleprime.c" , inside of singleprime.c trying create child morphs "isprime.exe" executable made out of "prime.c". want return number isprime.exe either 1 or 0 depending on if input number prime or not , store in childnum inside of main() function of "singleprime.c" can print terminal whether it's prime number or not based on 1 or 0 returned "isprime.exe". below 2 files:

prime.c:

/* file isprime.c  purpose: program checks if given number prime number  input: number - positive int  entered via command line parameters.  example isprime 1234  output: 0 - if input number not prime number 1 - if input number prime number 2 - if command line parameter not correct  assumption: program not check if number positive integer  */   #include "stdio.h" #include "stdlib.h" #include <unistd.h> #include "prime.h"  int main(int argc, char *argv[]) {         int i;          int number;          if (argc < 2) {             printf("returning 2");             return(2);         }         else number = atoi(argv[1]);         if (isprime(number)) {                 exit(1);         }         exit(0); }   /* purpose: check if input number prime number input: number - number checked  return: 0 - if number not prime number 1 - if number prime number */ int isprime(int number) {         int i;         for(i = 2; i*i < number; i++) {                 usleep(100);                 if (number % == 0) {                         printf("%d not prime number!",number);                         return(0);                 }         }         printf("%d prime number!",number);         return(1); } 

singleprime.c:

#include "stdio.h" #include "stdlib.h" #include <unistd.h> #include "prime.h"  int main(int argc, char *argv[]) {         int number, childnum;          if (!atoi(argv[1])) {                 printf("please use valid integer argument!");                 exit(1);         }          int pid = fork();          if (pid == 0) {                 wait(childnum);                 morph(argv[1]);         }          else {                 if (childnum == 0) {                         printf("the input number not prime number!");                         exit(1);                 }                 else if (childnum == 1) {                         printf("the input number prime number!");                         exit(1);                 }                 else if (childnum == 2) {                         printf("please input number greater 2!");                         exit(1);                 }         } }  void morph(char *number) {         char *primeargv[] = {                 "isprime.exe",                 number,                 null,         };          execvp("isprime.exe",primeargv);                } 

for starters, this

wait(childnum); 

should have made compiler issue clear warning, have drawn there wrong.

and indeed using wait() wrongly. expects pointer:

wait(int * status); 

use in following way:

  {     int status;     int result;          {       result = 0;       if ((pid_t) -1) == wait(&status)))       {         result = -1;         if (errno == eintr)         {           continue;         }         else         {           perror("wait() failed");         }       }        break;     } while (1);      if (-1 != result)     {       if (wifexited(status))       {         int ec = wexitstatus(status);         printf("the child's exit code %d\n", ec);       }       else       {         printf("the child did not provide exit code. crashed?\n");       }     }   } 

details can read in the documentation.

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also code somehow not make sense:

        if (pid == 0) {             wait(childnum);             morph(argv[1]);         } 

you calling wait() child, , after returned exec* isprime.exe.

you may want this

      pid = fork();       if (-1 == pid)       {          perror("fork() failed");       }       else if (pid == 0)        {         morph(argv[1]);       }       else       {         /* wait code shown above goes here.            childnum needs assigend. */         if (childnum == 0) {         ....       } 

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also^2 code not test whether call execvp() succeeded.

put perror("execvp() failed"); right after it.

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also^3 this

#include "stdio.h" #include "stdlib.h" 

should be

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