POSIX Thread Addition on XCode - c++

Question

The program should get arguments from a command line, and add the arguments via posix threads. But Xcode successfully builds it, but gives no output. Is there something wrong with this code.
Thanks
#include <iostream>
#include <pthread.h>
using namespace std;
void *Add(void *threadid){
long tid;
tid =(long)threadid;
long sum=0;
sum=sum+tid;
printf("%ld.\n",sum);
pthread_exit(NULL);
}
void *Print(void *threadid){
long tid;
tid =(long)threadid;
printf("%ld.\n",tid);
pthread_exit(NULL);
}
int main (int argc, char const *argv[])
{
if(argc<6){
printf("you need more arguments");
return -1;
}
long real[5];
pthread_t athread,bthread;
for (int x=1;x<=5;x++)
real[x-1]=atol(argv[x]);
for(int y=1;y<=5;y++)
pthread_create(athread[y],NULL,Add,(void *)&real[y]);
for(int y=1;y<=5;y++)
pthread_create(bthread[y],NULL,Print,(void *)&real[y]);
pthread_exit(NULL);
return 0;
}

Answer 1

First of all I think you should check if pthread_create method was success.
I don't have expirience in pthread under Apple, but based on that code I think you have problem with thread creation.

Answer 2

First of all, printf is defined in stdio.h and not in iostream. If you'd like to do it the C++ way with iostream, then cout << "Blabla " << var << endl; should be used instead.
Second, you are calling pthread_create with wrong arguments. As defined athread and bthread are not arrays but you use them as such. I am not entirely sure why this would even compile since pthread_create expects pthread_t* as first argument and you are providing *pthread_t. If the code ever compiles, it will most likely crash when run.
Third, you are not joining the adder threads. This means that your print threads could start before the adder threads have finished.
Fourth, you are summing into local variables. You are supposed to sum into a global one. Don't forget to guard the access to it by a mutex or something.
Fifth, arguments to the thread routines are wrong. You are passing pointer to the value and not the value itself and later reinterpreting the pointer as the value itself. You would most likely want to use (void *)real[y] and not (void *)&real[y]. Mind that casting long to void * doesn't work on all systems. On Mac OS X both long and void * are of the same length (either 32 or 64 bits) but this is not true in general.
Edited: Your code doesn't even compile on OS X:
$ g++ -o t.x t.cpp
t.cpp: In function ‘int main(int, const char**)’:
t.cpp:37: error: cannot convert ‘_opaque_pthread_t’ to ‘_opaque_pthread_t**’ for argument ‘1’ to ‘int pthread_create(_opaque_pthread_t**, const pthread_attr_t*, void* (*)(void*), void*)’
t.cpp:40: error: cannot convert ‘_opaque_pthread_t’ to ‘_opaque_pthread_t**’ for argument ‘1’ to ‘int pthread_create(_opaque_pthread_t**, const pthread_attr_t*, void* (*)(void*), void*)’
$ clang -o t.x t.cpp
t.cpp:37:5: error: no matching function for call to 'pthread_create'
pthread_create(athread[y],NULL,Add,(void *)&real[y]);
^~~~~~~~~~~~~~
/usr/include/pthread.h:304:11: note: candidate function not viable: no known
conversion from 'struct _opaque_pthread_t' to 'pthread_t *' (aka
'_opaque_pthread_t **') for 1st argument;
int pthread_create(pthread_t * __restrict,
^
t.cpp:40:5: error: no matching function for call to 'pthread_create'
pthread_create(bthread[y],NULL,Print,(void *)&real[y]);
^~~~~~~~~~~~~~
/usr/include/pthread.h:304:11: note: candidate function not viable: no known
conversion from 'struct _opaque_pthread_t' to 'pthread_t *' (aka
'_opaque_pthread_t **') for 1st argument;
int pthread_create(pthread_t * __restrict,
^
2 errors generated.
Don't you even see the error messages that XCode is providing?