How to print using g++ with printf correctly? - g++

Question

I am compiling this code with g++:
#include <pthread.h>
#include <iostream>
#include <cstdlib>
#include <string>
#include <stdio.h>
using namespace std;
#define num_threads 3
#define car_limit 4
pthread_mutex_t mutex; // mutex lock
pthread_t cid; // thread id
pthread_attr_t attr; // thread attrubutes
void *OneCar(void *dir);
void ArriveBridge(int *direction);
void CrossBridge();
void ExitBridge(int *direction);
int main()
{
int dir[3] = {0,1,1};
pthread_mutex_init(&mutex, NULL);
pthread_attr_init(&attr);
//cout<< "Pthread Create" << endl;
printf("Pthread Create\n");
for(int i = 0; i < num_threads; i++)
{
pthread_create(&cid, &attr, OneCar, (void *)&dir[i]);
}
return 0;
}
void ArriveBridge(int *direction)
{
//cout<<"Arrive"<<*direction << endl;
int dr;
if(*direction == 0)
dr=0;
else
dr=1;
printf("Arrive%d", dr);
}
void CrossBridge(int *dir)
{
char d;
if(*dir == 0)
d = 'N';
else
d = 'S';
//cout<<"Crossing Bridge going:"<<d<<endl;
printf("Crossing Bridge going %c", d);
}
void ExitBridge(int *direction)
{
//cout<<"Exit" <<*direction<<endl;
int dr;
if(*direction == 0)
dr=0;
else
dr=1;
printf("Exit%d\n", dr);
}
void *OneCar(void *dir)
{
int *cardir;
cardir = (int *) dir;
//cout<<*cardir;
ArriveBridge(cardir);
CrossBridge(cardir);
ExitBridge(cardir);
return 0;
}
and I am expecting this result printed to the screen:
> Pthread Create
> Arrive0Crossing Bridge going NExit0
> Arrive1Crossing Bridge going SExit1
> Arrive1Crossing Bridge going NExit1
But i get this instead:
Pthread Create
Arrive0Crossing Bridge going NExit0
Why doesnt it print the rest out?

Answer 1

You need to use "pthread_join" in main to wait for all threads to exit before your program terminates. You should also use an array to hold the id of each thread that you create:
pthread_t cid[num_threads]; // thread id`
You'll then want to call join on every thread you create:
for(int i = 0; i < num_threads; i++)
{
pthread_create(&cid[i], &attr, OneCar, (void *)&dir[i]);
}
for(int i = 0; i < num_threads; ++i)
{
pthread_join(cid[i], NULL);
};
Running the modified code now gives:
Pthread Create
Arrive0Crossing Bridge going NExit0
Arrive1Crossing Bridge going SExit1
Arrive1Crossing Bridge going SExit1

Answer 2

Have you tried joining your threads at the end of main? It could be that the program is terminating before the other threads are completely finished.

Answer 3

You missed the newlines ("\n"):
printf("Arrive%d\n", dr);
printf("Crossing Bridge going %c\n", d);
Because of that, the streams are probably not flushed. Additionally, if you don't wait for your threads (pthread_join) your program will exit before the threads could do their work.