Dealing with pointers causing a segmentation fault in C++ [closed] - c++

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Here is the function in question:
#include <cstdlib>
#include <string>
#include <iostream>
#include <unistd.h>
#include <pthread.h>
#include "Train.h"
#include "Platform.h"
const int NUM_TRAINS = 4;
const int NUM_NORTHERNLY_TRAINS = NUM_TRAINS / 2;
const int NUM_SOUTHERNLY_TRAINS = NUM_TRAINS - NUM_NORTHERNLY_TRAINS;
const int NUM_LOOPS = 16;
const char* TRAIN_NAME_ARRAY[NUM_TRAINS]
= { "Thomas the Tank-Engine",
"Percy the Small Engine",
"California Zephyr",
"Tokaido Shinkansen"
};
const int TRAIN_TRANSIT_TIME_MSECS[NUM_TRAINS]
= { 10000, // Thomas
10000, // Percy
5000, // CA Zephyr
1000 // Bullet train
};
Platform northBoundPlatform("North-bound Platform");
Platform southBoundPlatform("South-bound Platform");
void* initiallyNorthernly (void* vPtr)
{
Train* id = ((Train*)vPtr);
for (int i = 0; i < NUM_LOOPS; i++)
{
northBoundPlatform.arrive(id);
northBoundPlatform.leave();
pause();
southBoundPlatform.arrive(id);
southBoundPlatform.leave();
pause();
}
return((void*)id);
}
void* initiallySouthernly (void* vPtr)
{
Train* id = (Train*)vPtr;
for (int i = 0; i < NUM_LOOPS; i++)
{
southBoundPlatform.arrive(id);
southBoundPlatform.leave();
pause();
northBoundPlatform.arrive(id);
northBoundPlatform.leave();
pause();
}
return((void*)id);
}
int main ()
{
pthread_t tidArray[NUM_TRAINS];
Train* trainArray[NUM_TRAINS];
pthread_t tidArray2[NUM_NORTHERNLY_TRAINS];
Train* trainArray2[NUM_NORTHERNLY_TRAINS];
pthread_t tidArray3[NUM_SOUTHERNLY_TRAINS];
Train* trainArray3[NUM_SOUTHERNLY_TRAINS];
for (int i = 0; i < NUM_TRAINS; i++)
{ trainArray[i] = new Train(TRAIN_NAME_ARRAY[i],TRAIN_TRANSIT_TIME_MSECS[i]);
}
int trainInd = 0;
for (int i = 0; i < NUM_NORTHERNLY_TRAINS; i++)
{
pthread_create(&tidArray2[i], NULL, initiallyNorthernly,&trainArray2[i]);
}
for (int i = 0; i < NUM_SOUTHERNLY_TRAINS; i++)
{
pthread_create(&tidArray3[i], NULL, initiallySouthernly,&trainArray3[i]);
}
for (int i = 0; i < NUM_TRAINS; i++)
{
trainArray[i] = NULL;
// Wait for all Train threads. Also, get the pointers to the Train objects
// and delete() them because they were created by 'new'
pthread_join(tidArray[i], (void**)&trainInd);
pthread_join(tidArray2[i],(void**)&trainInd);
pthread_join(tidArray3[i],(void**)&trainInd);
}
return(EXIT_SUCCESS);
}
Here are the appropriate header files:
Train.h
class Train
{
std::string name_;
int pauseTimeUsecs_;
public :
Train (const std::string& newName,
int newPauseTimeUsecs
)
{
name_ = newName;
pauseTimeUsecs_ = newPauseTimeUsecs;
std::cout << getName() << " leaving the trainyard.\n";
}
~Train ()
{
std::cout << getName() << " going back to the trainyard\n";
}
const std::string&
getName ()
const
{ return(name_); }
void pause ()
const
{
usleep(pauseTimeUsecs_);
}
};
Platform.h
class Platform
{
std::string name_;
Train* trainPtr_;
pthread_mutex_t mutexLock_;
pthread_cond_t notEmptyCond_;
pthread_cond_t notFullCond_;
public :
Platform (const std::string& newName
)
{
name_ = newName;
trainPtr_ = NULL;
pthread_mutex_init(&mutexLock_,NULL);
pthread_cond_init(&notEmptyCond_,NULL);
pthread_cond_init(&notFullCond_,NULL);
}
// PURPOSE: To release resources. No parameters. No return value.
~Platform ()
{
pthread_mutex_destroy(&mutexLock_);
pthread_cond_destroy(&notEmptyCond_);
pthread_cond_destroy(&notFullCond_);
}
const std::string&
getName ()
const
{
return(name_);
}
Train* getTrainPtr
()
const
{
return(trainPtr_);
}
void arrive (Train* newTrainPtr
)
{
pthread_mutex_lock(&mutexLock_);
while (getTrainPtr() != NULL)
{
std::cout << getTrainPtr()->getName()
<< " is at " << getName()
<< ", " << newTrainPtr->getName()
<< " must wait.\n";
usleep(10) + rand() % 10;
pthread_cond_wait(&notFullCond_,&mutexLock_);
}
std::cout << newTrainPtr->getName() << " arriving at " << getName() << "\n";
trainPtr_ = newTrainPtr;
usleep(10 + rand() % 10);
pthread_mutex_unlock(&mutexLock_);
pthread_cond_signal(&notEmptyCond_);
}
Train* leave ()
{
pthread_mutex_lock(&mutexLock_);
while (getTrainPtr() == NULL)
{
std::cout << "No train at " << getName() << "!\n";
usleep(10 + rand() % 10);
pthread_cond_wait(&notEmptyCond_,&mutexLock_);
}
Train* toReturn = getTrainPtr();
std::cout << toReturn->getName() << " leaving " << getName() << "\n";
usleep(10 + rand() % 10);
trainPtr_ = NULL;
pthread_cond_signal(&notFullCond_);
pthread_mutex_unlock(&mutexLock_);
return(toReturn);
}
};
After running with gdb, the segmentation fault is occurring when I call arrive on northBoundPlatform(a Platform object). The goal of the function is to make the train object that is pointed to by vPtr arrive() at northernPlatform, leave() at northernPlatform, pause() on the train object, arrive() at the southBoundPlatform, leave() the southBoundPlatform, pause() on the object again, and finally return a pointer to the train that was used.
I am not sure if I am casting vPtr into a Train* correctly which is causing a segmentation fault. I can provide the rest of the main code if necessary. Any help is appreciated.

Answer 1

Your main() function has two for loops for each of NUM_NORTHERNLY_TRAINS, using initiallyNorthernly and initiallySouthernly, but the second loop should be looping with NUM_SOUTHERNLY_TRAINS instead.