Simulation program [closed] - c++

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Closed 10 years ago.
I'm making a simulation for severals queues.
I'm supposed to input number of queues in the beginning and then simulate all thoose.
Output for each queue each "round" is meantime, total number of served and size of each queue.
My program is crashing and dosen't respond.
It writes out the first queue och then crashes...
Help!
I think my calculations is wrong to but i don't know since it's all crashing.
Here it is:
#include <iostream>
#include <cstdlib>
#include <list>
#include <ctime>
#include<conio.h>
#include <time.h>
#include <stdlib.h>
#include<dos.h>
#include<windows.h>
using namespace std;
class Customer
{
public:
int servicet;
int served;
Customer()
{
servicet= rand()%150+30;
}
int getServicetime()
{
return servicet;
}
int getServed()
{
return served;
}
int decreaseServeTime()
{
servicet --;
}
};
int totServed=0;
int queues=0;
int inLine=0;
int totTime=0;
int smallestQueue=0;
int temp=0;
int ran=0;
double mean=0;
int served=0;
int serviceTime=0;
int help=0;
int sim=0;
int n=0;
using namespace std;
int main()
{
cout<<"Number of Cashiers?: "<<endl;
cin >> queues;
cout <<"How long simulation?: "<<endl;
cin >> sim;
list<Customer> *cashiers[queues];
list<Customer> *cust;
for(int i=0; i<=queues; i++)
{
cust = new list<Customer>;
cashiers[i] = cust;
}
srand(time(0));
while(n<sim)
{
Sleep(2000);
ran= rand()%4;
smallestQueue = cashiers[0] ->size();
for(int j=0; j<ran; j++)
{
for(int k=0; k<queues; k++)
{
temp = cashiers[k]->size();
if(temp<=smallestQueue)
{
smallestQueue = temp;
help=k;
}
}
Customer C;
cashiers[help]->push_back(C);
inLine++;
}
for(int i=0; i<queues; i++)
{
if(serviceTime>0)
{
serviceTime = cashiers[i]->front().getServicetime();
cashiers[i]->front().decreaseServeTime();
}
else if(serviceTime==0)
{
cashiers[i]->pop_front();
served++;
}
}
totTime++;
int cash=1;
for(int i=0; i<queues; i++)
{
if(inLine!=0)
{
cout <<"Kassa: "<<cash<<endl;
inLine = cashiers[i]->size();
mean = (totTime/inLine);
totServed +=served;
cash++;
}
cout <<inLine<<" "<<mean<<" "<<totServed<<endl;
}
n++;
}
system("pause");
}

Answer 1

I recommend that you use a program such as Application Verifier to find the issue that is causing the crash:
http://www.microsoft.com/en-us/download/details.aspx?id=20028
It's important that you learn how to debug your software and understand what is going on. Please run your code in a debugger (Visual Studio, Eclipse) and take a look at where it stops. If you used Application Verifier, then it will likely stop where the issue originates. Take a look at the variables and see whether they make sense. Look at whether you're accessing memory locations you shouldn't.
To use Application Verifier with Visual Studio, install it then find the appVerifier.exe in the System32 folder in C:\Windows. Then open the file and point it to your executable. Enable what you think are the proper checks. Then run it in visual Studio.

Answer 2

A good place to start is with a debugger (e.g. gdb). First we compile with debugging enabled (g++ -ggdb) and try running in the debugger,
$ g++ hi.cpp -ggdb
$ gdb ./a.out
GNU gdb (GDB) 7.5-ubuntu
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/ben/a.out...done.
(gdb) run
Starting program: /home/ben/a.out
Number of Cashiers?:
5
How long simulation?:
5
Kassa: 1
Program received signal SIGSEGV, Segmentation fault.
0x0000000000401827 in std::_List_const_iterator<Customer>::operator++ (
this=0x7fffffffdd10) at /usr/include/c++/4.7/bits/stl_list.h:236
236 _M_node = _M_node->_M_next;
(gdb) backtrace
#0 0x0000000000401827 in std::_List_const_iterator<Customer>::operator++ (
this=0x7fffffffdd10) at /usr/include/c++/4.7/bits/stl_list.h:236
#1 0x0000000000401665 in std::__distance<std::_List_const_iterator<Customer> >
(__first=..., __last=...)
at /usr/include/c++/4.7/bits/stl_iterator_base_funcs.h:82
#2 0x0000000000401492 in std::distance<std::_List_const_iterator<Customer> > (
__first=..., __last=...)
at /usr/include/c++/4.7/bits/stl_iterator_base_funcs.h:118
#3 0x000000000040135b in std::list<Customer, std::allocator<Customer> >::size
(this=0x604010) at /usr/include/c++/4.7/bits/stl_list.h:855
#4 0x0000000000401122 in main () at hi.cpp:125
Here we see that the program crashed with a segmentation fault in a
function of the std::list. After programming for a while, you will
gain an intuition that this is probably due to your program trampling
on some memory it shouldn't be. Having identified roughly the nature
of the problem, we will now switch to valgrind, a tool for tracking
down specifically this sort of issue.
$ valgrind ./a.out
==13751== Memcheck, a memory error detector
==13751== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==13751== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==13751== Command: ./a.out
==13751==
Number of Cashiers?:
5
How long simulation?:
5
Kassa: 1
==13751== Invalid read of size 8
==13751== at 0x401422: std::list<Customer, std::allocator<Customer> >::begin() const (stl_list.h:749)
==13751== by 0x40134F: std::list<Customer, std::allocator<Customer> >::size() const (stl_list.h:855)
==13751== by 0x401121: main (hi.cpp:125)
==13751== Address 0x5a06040 is 0 bytes inside a block of size 16 free'd
==13751== at 0x4C2A44B: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==13751== by 0x4018E7: __gnu_cxx::new_allocator<std::_List_node<Customer> >::deallocate(std::_List_node<Customer>*, unsigned long) (new_allocator.h:100)
==13751== by 0x4017D9: std::_List_base<Customer, std::allocator<Customer> >::_M_put_node(std::_List_node<Customer>*) (stl_list.h:339)
==13751== by 0x4015C0: std::list<Customer, std::allocator<Customer> >::_M_erase(std::_List_iterator<Customer>) (stl_list.h:1549)
==13751== by 0x4013E9: std::list<Customer, std::allocator<Customer> >::pop_front() (stl_list.h:983)
==13751== by 0x40108B: main (hi.cpp:113)
==13751==
==13751==
==13751== Process terminating with default action of signal 8 (SIGFPE)
==13751== Integer divide by zero at address 0x402CCCE98
==13751== at 0x40113C: main (hi.cpp:126)
Here we see valgrind telling us that your program attempted a read
operation on unallocated memory. In particular, this seems to be
happening as a result of a pop_front operation. Looking at the
source, you indeed attempt to pop from cashiers[i] without first
checking it's size.
We can add an appropriate check,
...
else if(serviceTime==0)
{
if (!cashiers[i]->empty()) {
cashiers[i]->pop_front();
served++;
}
}
...
The actual cause of the crash, however, is a division by zero in computing the
mean, as noted at the end of valgrind's output. This is due to the fact that the case where no Customers are inLine is not handled when computing mean.