I'm making a small file reading and data validation program as part of my TAFE (a tertiary college) course, This includes checking and validating dates.
I decided that it would be best done with a seperate class, rather than integrating it into my main driver class.
The problem is that I'm getting a segmentation fault(core dumped) after my test program runs. Near as I can tell, the error occurs when the program terminates, popping up after the destructor is called. So far I have had no luck finding the cause of this fault, and was hoping that some enlightened soul might show me the error of my ways.
date.h
#ifndef DATE_H
#define DATE_H
#include <string>
using std::string;
#include <sstream>
using std::stringstream;
#include <cstdlib>
using std::exit;
#include <iostream>
using std::cout;
using std::endl;
class date {
public:
explicit date();
~date();
bool before(string dateIn1, string dateIn2);
int yearsBetween(string dateIn1, string dateIn2);
bool isValid(string dateIn);
bool getDate(int date[], string dateIn);
bool isLeapYear(int year);
private:
int days[];
};
#endif
date.cpp
#include "date.h"
date::date() {
days[0] = 31;
days[1] = 28;
days[2] = 31;
days[3] = 30;
days[4] = 31;
days[5] = 30;
days[6] = 31;
days[7] = 31;
days[8] = 30;
days[9] = 31;
days[10] = 30;
days[11] = 31;
}
bool date::before(string dateIn1, string dateIn2) {
int date1[3];
int date2[3];
getDate(date1, dateIn1);
getDate(date2, dateIn2);
if (date1[2] < date2[2]) {
return true;
} else if (date1[1] < date2[1]) {
return true;
} else if (date1[0] < date2[0]) {
return true;
}
return false;
}
date::~date() {
cout << "this is for testing only, plox delete\n";
}
int date::yearsBetween(string dateIn1, string dateIn2) {
int date1[3];
int date2[3];
getDate(date1, dateIn1);
getDate(date2, dateIn2);
int years = date2[2] - date1[2];
if (date1[1] > date2[1]) {
years--;
}
if ((date1[1] == date2[1]) && (date1[0] > date2[1])) {
years--;
}
return years;
}
bool date::isValid(string dateIn) {
int date[3];
if (getDate(date, dateIn)) {
if (date[1] <= 12) {
int extraDay = 0;
if (isLeapYear(date[2])) {
extraDay++;
}
if ((date[0] + extraDay) <= days[date[1] - 1]) {
return true;
}
}
} else {
return false;
}
}
bool date::getDate(int date[], string dateIn) {
string part1, part2, part3;
size_t whereIs, lastFound;
whereIs = dateIn.find("/");
part1 = dateIn.substr(0, whereIs);
lastFound = whereIs + 1;
whereIs = dateIn.find("/", lastFound);
part2 = dateIn.substr(lastFound, whereIs - lastFound);
lastFound = whereIs + 1;
part3 = dateIn.substr(lastFound, 4);
stringstream p1(part1);
stringstream p2(part2);
stringstream p3(part3);
if (p1 >> date[0]) {
if (p2>>date[1]) {
return (p3>>date[2]);
} else {
return false;
}
return false;
}
}
bool date::isLeapYear(int year) {
return ((year % 4) == 0);
}
and Finally, the test program
#include <iostream>
using std::cout;
using std::endl;
#include "date.h"
int main() {
date d;
cout << "1/1/1988 before 3/5/1990 [" << d.before("1/1/1988", "3/5/1990")
<< "]\n1/1/1988 before 1/1/1970 [" << d.before("a/a/1988", "1/1/1970")
<<"]\n";
cout << "years between 1/1/1988 and 1/1/1998 ["
<< d.yearsBetween("1/1/1988", "1/1/1998") << "]\n";
cout << "is 1/1/1988 valid [" << d.isValid("1/1/1988") << "]\n"
<< "is 2/13/1988 valid [" << d.isValid("2/13/1988") << "]\n"
<< "is 32/12/1988 valid [" << d.isValid("32/12/1988") << "]\n";
cout << "blerg\n";
}
I've left in some extraneous cout statements, which I've been using to try and locate the error.
I thank you in advance.
Change:
private:
int days[];
to:
private:
int days[12];
The problem is that you never actually initialize the days field in the type date. This means that when you are setting the values in the constructor you are accessing uninitialized memory.
You need to explicitly initialize the days value in some way. The easiest fix is to use a vector for the type or to hard code the size of the array to 12.
private:
int days[12];
Or
private:
std:vector<int> days;
...
date::date() {
days.push_back(31);
days.push_back(28);
...
}
You don't say which compiler you are using, but if I compile this code using g++ with the -Wall and -pedantic flags:
struct S {
int a[];
};
int main() {
S s;
}
I get the warning message:
warning: ISO C++ forbids zero-size array 'a'
The moral is that you should always compile using as many compiler warnings as possible - it can save you mountains of time and result in more correct code.
int days[];
This is a non-standard extension. You must specify a size for the array, such as:
static const MonthCount = 12;
int days[MonthCount];
To actually have an array to use. Otherwise you have a "zero-sized array" (not standard!). Your program is tromping over memory every time you use any element of your current array.
I agree with the previous answers to this question, but I would add the rationale for their correctness:
Segmentation faults are caused whenever you attempt to access memory you are not allowed to access.
http://en.wikipedia.org/wiki/Segmentation_fault
You were not allowed to access "days[0]" through days "[11]" because the computer had not given the "days[]" variable that you declared enough memory to hold any elements, thus when you tried to access said elements, it threw a segfault.
Any variables not declared with the "new" operator are placed on the "stack," which is a contiguous chunk of memory the computer has sectioned away for use by the program. In order to keep everything stored in the stack contiguous, the computer will only give exactly the amount memory you require for you to use whenever you request it, so that if you request to create an int, for example, it will only give you enough memory to store that single int.
When you wrote the line int days[]; the computer attempted to evaluate how much memory it would require, assessed it as an empty array, and gave you enough memory to store said empty array. Because the computer did not give your array any extra space beyond what was needed for an empty array, it knew that the memory you tried to access in that array had not been assigned to it, so it threw a segmentation fault and crashed.
If you have not yet learned about the "stack" and "heap" in your computer science class, then sorry if this is a bit overwhelming, but I perhaps overcomplicated things, and I think you likely soon will.
Related
I have been working on a project for my computer science class and have encountered an issue with the code working. I am shown no error except when I try to compile and I get an error that reads:
Exception thrown: write access violation.
_Left was 0xCCCCCCCC.
The purpose of my project is to take a list of names from an external file, read them into an array, sort said array and then output the sorted list all while using a class for the code.
Here is a copy of my code and I would like to extend my gratitude to whoever can help me through my issue:
**Header File**
#include <iostream>
using namespace std;
class person
{
public:
person();
bool get(ifstream&);
void put(ofstream&);
private:
int capacity = 0;
string first_name[CAPACITY];
string last_name[CAPACITY];
int age[CAPACITY];
};```
**Header function definitions cpp file**
#include<iostream>
#include<string>
#include<fstream>
#include<cstdlib>
const int CAPACITY=20;
using namespace std;
#include "Person.h"
//Names constructor
//Postcondition both first name and last name initialized to zero
person::person()
{
first_name[CAPACITY] = "";
last_name[CAPACITY] = "";
age[CAPACITY]=0;
}
bool person::get(ifstream& in)
{
in >> first_name[CAPACITY] >> last_name[CAPACITY] >> age[CAPACITY];
return(in.good());
}
void person::put(ofstream &out)
{
out << first_name[CAPACITY] << last_name[CAPACITY] << age[CAPACITY];
}
**cpp file which holds main**
#include<iostream>
#include<cstdlib>
#include<fstream>
#include<string>
const int CAPACITY = 20;
using namespace std;
#include "Person.h"
void pop(string *xp, string *yp);
void sort(string name[CAPACITY], int count);
int main()
{
class person names[CAPACITY];
ifstream infile;
ofstream outfile;
string filename;
string name[CAPACITY];
int n = 0;
cout << "Enter the file name you wish to open" << endl;
cin >> filename;
infile.open(filename + ".txt");
outfile.open("Person_New.txt");
if (infile.fail())
{
cout << "The file requested did not open" << endl;
exit(1);
}
while (!infile.eof())
{
names[n].get(infile);
n++;
}
sort(name, CAPACITY);
for (int i = 0; i < CAPACITY; i++)
{
names[i].put(outfile);
}
cout << "The file has been created" << endl;
infile.close();
}
void pop(string *xp, string *yp)
{
string temp = *xp;
*xp = *yp;
*yp = temp;
}
void sort(string name[CAPACITY], int count)
{
int i, j;
for (i = 0; i < count - 1; i++)
{
for (j = 0; j < count - i - 1; j++)
{
if (name[j] > name[j + 1])
{
pop(&name[j], &name[j + 1]);
}
}
}
}
Once again Thank you for any support
It sounds to me like the compiler is getting upset that you are trying to write (i.e. assign a value) at an address that you do not have permission to access. I believe your constructor for the class person might be at fault because of how this class stores its variables, as well as the class header:
Constructor for the class person:
`person::person(){
first_name[CAPACITY] = "";
last_name[CAPACITY] = "";
age[CAPACITY] = 0;
}`
Class header for the class person:
`class person{
public:
//stuff
private:
int capacity = 0;
std::string first_name[CAPACITY];
std::string last_name[CAPACITY];
int age[CAPACITY];
//more stuff
}`
C++ is very specific about its naming conventions, so it makes a distinction between capacity and CAPACITY. Because of this, the variable CAPACITY is not defined within the Person.h file.
Also, because CAPACITY is set to a fixed value in your Person.cpp file, whenever you use first_name[CAPACITY], last_name[CAPACITY], or age[CAPACITY] to assign new values, you are only updating the values at the index equal to CAPACITY unless you update the value of CAPACITY itself. In the code you provided, CAPACITY is equal to 20, so your program attempts to update exclusively index 20 with each method call. This will likely cause issues since the person class only attempts to make its arrays on the runtime stack, with a size of 0 each.
Separately, it seems like you want an array of people, but it appears that you are attempting to use a single person object to store the names and ages of multiple people by making these all arrays. Instead, I would recommend making first_name, last_name, and age not arrays, but rather single variables. Then, you can manipulate an array of type person using your CAPACITY variable. You got pretty close, but you can instead declare it as person myPersonArray[CAPACITY] (no need to mention "class" in front of it -- just be sure that you have #include "Person.h" in your main.cpp file). When you want to update a specific person, you can perform an operation like myPersonArray[updateThisIndexNum].update(newFirstName, newLastName, newAge) or some logical equivalent.
As a final note, I almost always highly recommend against using !infile.eof() to control your while loop when reading any file because eof() only indicates whether you have tried to read past the end of an input file. I would highly recommend checking out this post on Stack Overflow where people far more knowledgeable than I explain exactly why this is usually dangerous and how to avoid it.
So I'm trying to make a bubble sort algorithm in class and I'm having this problem where it keeps giving me an error when I'm trying to find the length of the list where it says "expression must have a class type" and for the life of me I cannot figure out what to do. the tutorial I'm using isn't an help and I cannot find any other people with the same problem.
if anyone gets what it is asking I would appreciate the help, and any explanation would also be appreciated as I'm still new and would like to understand so I can try to learn
this was all done on VS 2017 (the free version)
#include "pch.h"
#include <iostream>
using std::cout;
using std::endl;
int main()
{
bool found = true;
int target{ 0 };
int temp{};
bool ordered{ false };
int list[10] = { 4,6,5,1,3,2,10,8,9,7 };
cout << list.length() << endl;
bool swapped{ false };
while (ordered = false)
{
target = 0;
while (target != list.length)
{
if (list[target] > list[target + 1])
{
swapped == true;
list[target] = temp;
list[target] = list[target + 1];
list[target + 1] = temp;
target = target + 1;
}
else
{
target = target + 1;
}
}
if (swapped == false)
{
ordered = true;
}
}
cout << list << endl;
getchar();
return 0;
}
link to the photo of the error message
The error you have mentioned ("expression must have a class type") is caused by the below statement and other similar statements :
cout << list.length() << endl;
list is an integer array of size 10 as per this statement int list[10];
So you cannot use a . on it. You can use the . operator on a structure or class or union only. And even if list were a class/structure, length() method should be defined in it for the above to work.
Instead you should use sizeof operator. You can store it in a variable and use it later on.
size_t length = sizeof list/sizeof list[0];
cout << length << endl;
So I am new to c++, coming from C#. This is giving me several errors when compiling, which all seem to relate to this object declaration. Anyone able to show me the right way to do this?
I get an undeclared identifier where i declare tri(sideLength).
I have used this as a reference for object declaration, but it doesn't seem to be helping me.
Thanks.
#include <iostream> // Provides cout
#include <iomanip> // Provides setw function for setting output width
#include <cstdlib> // Provides EXIT_SUCCESS
#include <cassert> // Provides assert function
#include <stdexcept>
#include <math.h>
using namespace std; // Allows all standard library items to be used
void setup_cout_fractions(int fraction_digits)
// Precondition: fraction_digits is not negative.
// Postcondition: All double or float numbers printed to cout will now be
// rounded to the specified digits on the right of the decimal.
{
assert(fraction_digits > 0);
cout.precision(fraction_digits);
cout.setf(ios::fixed, ios::floatfield);
if (fraction_digits == 0)
cout.unsetf(ios::showpoint);
else
cout.setf(ios::showpoint);
}
int main()
{
const int MAX_SIDE_LENGTH = 6;
const int INITIAL_LENGTH = 1;
const int DIGITS = 4;
const int ARRAY_SIZE = 6;
// Set up the output for fractions and print the table headings.
setup_cout_fractions(DIGITS);
// Each iteration of the loop prints one line of the table.
for (int sideLength = 0; sideLength < MAX_SIDE_LENGTH; sideLength += 1)
{
EquilateralTriangle tri(sideLength);
//Square sq(sideLength);
//Pentagon_Reg pent(sideLength);
//Hexagon_Reg hex(sideLength);
//Heptagon_Reg hept(sideLength);
//Octagon_Reg octa(sideLength);
cout << "Type: " << tri.Name() << "has area: " << tri.Area() << " with SideLength = " << sideLength;
}
return EXIT_SUCCESS;
}
//Template
class GeometricFigure
{
public:
GeometricFigure() { }
double SideLength;
virtual double Area() { return 0; };
virtual char* Name() { return ""; };
};
class EquilateralTriangle : public GeometricFigure {
public:
EquilateralTriangle(double sideLength)
{
SideLength = sideLength;
}
char* Name() { return "Equilateral Triangle"; }
double Area() { return (sqrt(3) / 2 * pow(SideLength, 2)); }
};
In C++, the compiler reads your code from top-to-bottom, once. This is a holdover from when early C compilers only had a few kilobytes of memory to work with - C was designed so that a compiler would only need to look at a little bit of the code at a time.
Because of this, things must have been declared or defined as necessary, before you try to use them.
Move both classes somewhere before main. GeometricFigure must be before EquilateralTriangle, and EquilateralTriangle must be before main.
You would need to "declare" or tell the compiler, where to look for the EquilateralTriangle and GeometricFigure, "before" you use it first. you might want to take a look at the similar discussion at - C# declarations vs definitions
I'm Java user coming over to C++, and I am having a hard time understanding what is going wrong with this statement. My program has been segfaulting anywhere I put the push_back command. So I'm wondering what exactly is going on.
class Process {
public:
int nice;
int arrivalTime;
int cpuBursts;
list<int> burstList;
Process() {
burstList.push_back(10); // Segfaults here...
}
};
Here is the full code:
#include<iostream>
#include<stdlib.h>
#include<fstream>
#include<list>
#include<string.h>
using namespace std;
int calcTimeslice(int priority);
int calcOriginalPrio(int nice);
int readFile(int ,char **);
int calcPrioBonus(int,int);
void tokenizeAndAdd(char *);
class Bursts {
public:
int isCPUBurst;
int time;
Bursts() {}
// Constructor to make it easier to add to list
Bursts(int tempIsCPU, int tempTime) {
isCPUBurst = tempIsCPU;
time = tempTime;
}
};
class Process {
public:
int nice;
int arrivalTime;
int cpuBursts;
list<int> burstList;
Process() {
burstList.push_back(10);
}
};
int main(int arg, char **argv) {
// This is if the file was not correctly read into the program
// or it doesnt exist ...
if(readFile(arg,argv)==-1) {
cout << "File could not be read. \n";
return -1;
}
//cout << "Original Calc Whatever: " << calcOriginal(19) << '\n';
return 0;
}
/*
* Calculates the timeslice based on the priority
*/
int calcTimeslice(int priority) {
double finalCalc;
// This is the given function in the prompt
finalCalc = ( (1 - (priority / 140)) * 290 + (.5) ) + 10;
// Cast to int, this will be a truncate
return ((int)finalCalc);
}
int readFile(int arg, char **argv) {
char *temp,*pointer;
int endOfFile = 1;
// While its not the end of the file
while(endOfFile) {
// Read in the input from stdin
fgets(temp,256,stdin);
// Check to see if this line had a * in it
if(*temp =='*')
endOfFile = 0;
else
tokenizeAndAdd(temp);
}
return 0;
}
void tokenizeAndAdd(char *string) {
char *token = strtok(string," \n");
int i = 0;
Process p;
while(token != NULL) {
cout << token << endl;
if(i>2) { // If it is odd (CPU burst)
if(i%2 == 1) {
int tempInt = atoi(token);
//p.burstList.push_back(tempInt);
}
else { // If it is even (IO burst)
int tempInt = atoi(token);
//p.burstLis.push_back(tempInt);
}
}
else if(i==0)
p.nice = atoi(token);
else if(i==1)
p.arrivalTime = atoi(token);
else if(i==2)
p.cpuBursts = atoi(token);
token = strtok(NULL," \n");
i++;
}
//cout << p.nice << " " << p.arrivalTime << " " << p.cpuBursts << "\n";
//i = 0;
//cout << p.burstList.size() << "\n";
// cout <<
//}
return;
}
/*
* Calculates and returns the original priority based on the nice number
* provided in the file.
*/
int calcOriginalPrio(int nice) {
double finalCalc;
// This is the given function from the prompt
finalCalc = (( nice + 20 ) / 39 ) * 30 + 105.5;
// Cast to int, this is a truncate in C++
return ((int)finalCalc);
}
/*
* Calculates the bonus time given to a process
*/
int calcPrioBonus(int totalCPU, int totalIO) {
double finalCalc;
// How to calculate bonus off of the prompt
if(totalCPU < totalIO)
finalCalc = ( (1 - (totalCPU / (double)totalIO)) * (-5)) - .5;
else
finalCalc = ( (1 - (totalIO / (double)totalCPU)) * 5) + .5;
// Cast to int
return ((int)finalCalc);
}
You are using temp uninitialized in the following code:
char *temp;
...
while(endOfFile) {
fgets(temp,256,stdin);
...
This can have any side effect, since it most likely destroys your stack or parts of the heap memory. It could fail immediately (when calling the fgets() function), it could fail later (as in your sample) or it could even run fine - maybe until you upgrade your OS, your compiler or anything else, or until you want to run the same executable on another machine. This is called undefined behaviour.
You need to allocate space for the temp variable, not a pointer only. Use something like
char temp[256];
...
while(endOfFile) {
fgets(temp,256,stdin);
...
For more information, see the fgets() documentation. The first parameter is a pointer to a char array - that is where fgets() will store the bytes which have been read. In your code, you pass an uninitialized pointer which means that fgets() will store the bytes to an undefined memory location - this is catched by the OS which terminates your application with a segmentation fault.
BTW: You should consider enabling pedantic warnings when compiling - I compiled with
g++ -Wall -pedantic -o list list.cpp
which gave me the following warning:
list.cpp: In function 'int readFile(int, char**)':
list.cpp:76:26: warning: 'temp' may be used uninitialized in this function [-Wuninitialized]
This is probably not the actual code with the error you report. But here is one of the problems with give you UB.
char *temp,*pointer; // uninicialized pointer char temp[1000]; could work?
int endOfFile = 1;
// While its not the end of the file
while(endOfFile) {
// Read in the input from stdin
fgets(temp,256,stdin);
The last function call will read a maximum of 256 bytes from stdin and will write it in the memory pointed by pointer tmp. So, you need to first "prepare" that memory. But with char *tmp; you only define a pointer, with no defined value, that is, with point to some possible unexisting or illegal/inaccessible for you memory. In contrary, char tmp[1000]; will define in the "stack memory" a block of 1000 bytes, with you can point to using simple the variable tmp. Hope this is clear for you.
EDIT:
I don't know why that would change the behavior of the list,
You are right. That is Undefined Behavior (UB). When you write in some unknown memory (pointed by an uninitialized pointer) you may overwrite data or even code that will broke somewhere the correct function of your program in an unpredicted way.
You will need to learn more about pointers but better you use std::string, and look how parse your file using string and stringstream. That will manage for you the memmory,
I am trying to write a logger class for my C++ calculator, but I'm experiencing a problem while trying to push a string into a list.
I have tried researching this issue and have found some information on this, but nothing that seems to help with my problem. I am using a rather basic C++ compiler, with little debugging utilities and I've not used C++ in quite some time (even then it was only a small amount).
My code:
#ifndef _LOGGER_H_
#define _LOGGER_H_
#include <iostream>
#include <list>
#include <string>
using std::cout;
using std::cin;
using std::endl;
using std::list;
using std::string;
class Logger
{
private:
list<string> mEntries;
public:
Logger() {}
~Logger() {}
// Public Methods
void WriteEntry(const string& entry)
{
mEntries.push_back(entry);
}
void DisplayEntries()
{
cout << endl << "**********************" << endl
<< "* Logger Entries *" << endl
<< "**********************" << endl
<< endl;
for(list<string>::iterator it = mEntries.begin();
it != mEntries.end(); it++)
{
// *** BELOW LINE IS MARKED WITH THE ERROR ***
cout << *it << endl;
}
}
};
#endif
I am calling the WriteEntry method by simply passing in a string, like so:
mLogger->WriteEntry("Testing");
Any advice on this would be greatly appreciated.
* CODE ABOVE HAS BEEN ALTERED TO HOW IT IS NOW *
Now, the line:
cout << *it << endl;
causes the same error. I'm assuming this has something to do with how I am trying to get the string value from the iterator.
The code I am using to call it is in my main.cpp file:
#include <iostream>
#include <string>
#include <sstream>
#include "CommandParser.h"
#include "CommandManager.h"
#include "Exceptions.h"
#include "Logger.h"
using std::string;
using std::stringstream;
using std::cout;
using std::cin;
using std::endl;
#define MSG_QUIT 2384321
#define SHOW_LOGGER true
void RegisterCommands(void);
void UnregisterCommands(void);
int ApplicationLoop(void);
void CheckForLoggingOutput(void);
void ShowDebugLog(void);
// Operations
double Operation_Add(double* params);
double Operation_Subtract(double* params);
double Operation_Multiply(double* params);
double Operation_Divide(double* params);
// Variable
CommandManager *mCommandManager;
CommandParser *mCommandParser;
Logger *mLogger;
int main(int argc, const char **argv)
{
mLogger->WriteEntry("Registering commands...\0");
// Make sure we register all commands first
RegisterCommands();
mLogger->WriteEntry("Command registration complete.\0");
// Check the input to see if we're using the program standalone,
// or not
if(argc == 0)
{
mLogger->WriteEntry("Starting application message pump...\0");
// Full version
int result;
do
{
result = ApplicationLoop();
} while(result != MSG_QUIT);
}
else
{
mLogger->WriteEntry("Starting standalone application...\0");
// Standalone - single use
// Join the args into a string
stringstream joinedStrings(argv[0]);
for(int i = 1; i < argc; i++)
{
joinedStrings << argv[i];
}
mLogger->WriteEntry("Parsing argument '" + joinedStrings.str() + "'...\0");
// Parse the string
mCommandParser->Parse(joinedStrings.str());
// Get the command names from the parser
list<string> commandNames = mCommandParser->GetCommandNames();
// Check that all of the commands have been registered
for(list<string>::iterator it = commandNames.begin();
it != commandNames.end(); it++)
{
mLogger->WriteEntry("Checking command '" + *it + "' is registered...\0");
if(!mCommandManager->IsCommandRegistered(*it))
{
// TODO: Throw exception
mLogger->WriteEntry("Command '" + *it + "' has not been registered.\0");
}
}
// Get each command from the parser and use it's values
// to invoke the relevant command from the manager
double results[commandNames.size()];
int currentResultIndex = 0;
for(list<string>::iterator name_iterator = commandNames.begin();
name_iterator != commandNames.end(); name_iterator++)
{
string paramString = mCommandParser->GetCommandValue(*name_iterator);
list<string> paramStringArray = StringHelper::Split(paramString, ' ');
double params[paramStringArray.size()];
int index = 0;
for(list<string>::iterator param_iterator = paramStringArray.begin();
param_iterator != paramStringArray.end(); param_iterator++)
{
// Parse the current string to a double value
params[index++] = atof(param_iterator->c_str());
}
mLogger->WriteEntry("Invoking command '" + *name_iterator + "'...\0");
results[currentResultIndex++] =
mCommandManager->InvokeCommand(*name_iterator, params);
}
// Output all results
for(int i = 0; i < commandNames.size(); i++)
{
cout << "Result[" << i << "]: " << results[i] << endl;
}
}
mLogger->WriteEntry("Unregistering commands...\0");
// Make sure we clear up our resources
UnregisterCommands();
mLogger->WriteEntry("Command unregistration complete.\0");
if(SHOW_LOGGER)
{
CheckForLoggingOutput();
}
system("PAUSE");
return 0;
}
void RegisterCommands()
{
mCommandManager = new CommandManager();
mCommandParser = new CommandParser();
mLogger = new Logger();
// Known commands
mCommandManager->RegisterCommand("add", &Operation_Add);
mCommandManager->RegisterCommand("sub", &Operation_Subtract);
mCommandManager->RegisterCommand("mul", &Operation_Multiply);
mCommandManager->RegisterCommand("div", &Operation_Divide);
}
void UnregisterCommands()
{
// Unregister each command
mCommandManager->UnregisterCommand("add");
mCommandManager->UnregisterCommand("sub");
mCommandManager->UnregisterCommand("mul");
mCommandManager->UnregisterCommand("div");
// Delete the logger pointer
delete mLogger;
// Delete the command manager pointer
delete mCommandManager;
// Delete the command parser pointer
delete mCommandParser;
}
int ApplicationLoop()
{
return MSG_QUIT;
}
void CheckForLoggingOutput()
{
char answer = 'n';
cout << endl << "Do you wish to view the debug log? [y/n]: ";
cin >> answer;
switch(answer)
{
case 'y':
ShowDebugLog();
break;
}
}
void ShowDebugLog()
{
mLogger->DisplayEntries();
}
// Operation Definitions
double Operation_Add(double* values)
{
double accumulator = 0.0;
// Iterate over all values and accumulate them
for(int i = 0; i < (sizeof values) - 1; i++)
{
accumulator += values[i];
}
// Return the result of the calculation
return accumulator;
}
double Operation_Subtract(double* values)
{
double accumulator = 0.0;
// Iterate over all values and negativel accumulate them
for(int i = 0; i < (sizeof values) - 1; i++)
{
accumulator -= values[i];
}
// Return the result of the calculation
return accumulator;
}
double Operation_Multiply(double* values)
{
double accumulator = 0.0;
for(int i = 0; i < (sizeof values) - 1; i++)
{
accumulator *= values[i];
}
// Return the value of the calculation
return accumulator;
}
double Operation_Divide(double* values)
{
double accumulator = 0.0;
for(int i = 0; i < (sizeof values) - 1; i++)
{
accumulator /= values[i];
}
// Return the result of the calculation
return accumulator;
}
Did you remember to call mLogger = new Logger at some point? Did you accidantally delete mLogger before writing to it?
Try running your program in valgrind to see whether it finds any memory errors.
After your edit, the solution seem clear:
Your first line in main() is :
mLogger->WriteEntry("Registering commands...\0");
Here mLogger is a pointer that has never been initialized. This is "undefined behaviour", meaning anything can appen, often bad things.
To fix this you can either make it a "normal" variable, not a pointer or create a Logger instance using new (either at the declaration or as the first line in main).
I suggest you to not use a pointer to be sure the logger is always there and is automatically destroyed.
By the way, it seems like you want to create every instance of objects on the heap using pointers. It's not recommanded if it's not necessary. You should use pointers ONLY if you want to explicitely state the creation (using new) and destruction (using delete) of the instance object. If you just need it in a specific scope, don't use a pointer. You might come from another language like Java or C# where all objects are referenced. If so, you should start learning C++ like a different language to avoid such kind of problem. You should learn about RAII and other C++ scpecific paradigm that you cannot learn in those languages. If you come from C you should too take it as a different language. That might help you avoid complex problems like the one you showed here. May I suggest you read some C++ pointer, references and RAII related questions on stackoverflow.
First, you don't need to create the std::list on the heap. You should just use it as a normal member of the class.
class Logger
{
private:
list<string> mEntries; // no need to use a pointer
public:
Logger() // initialization is automatic, no need to do anything
{
}
~Logger() // clearing and destruction is automatic too, no need to do anything
{
}
//...
};
Next, entryData don't exist in this code so I guess you wanted to use entry. If it's not a typo then you're not providing the definition of entryData that is certainly the source of your problem.
In fact I would have written your class that way instead:
class Logger
{
private:
list<string> mEntries;
public:
// no need for constructor and destructor, use the default ones
// Public Methods
void WriteEntry(const string& entry) // use a const reference to avoid unnecessary copy (even with optimization like NRVO)
{
mEntries.push_back( entry ); // here the list will create a node with a string inside, so this is exactly like calling the copy constructor
}
void DisplayEntries()
{
cout << endl << "**********************" << endl
<< "* Logger Entries *" << endl
<< "**********************" << endl
<< endl;
for(list<string>::iterator it = mEntries.begin();
it != mEntries.end(); ++it) // if you want to avoid unnecessary copies, use ++it instead of it++
{
cout << *it << endl;
}
}
};
What's certain is that your segfault is from usage outside of this class.
Is an instance of Logger being copied anywhere (either through a copy constructor or operator=)? Since you have mEntries as a pointer to a list, if you copy an instance of Logger, they will share the value of the pointer, and when one is destructed, it deletes the list. The original then has a dangling pointer. A quick check is to make the copy constructor and operator= private and not implemented:
private:
void operator=(const Logger &); // not implemented
Logger(const Logger &); // not implemented
When you recompile, the compiler will flag any copies of any Logger instances.
If you need to copy instances of Logger, the fix is to follow the Rule of 3:
http://en.wikipedia.org/wiki/Rule_of_three_%28C%2B%2B_programming%29
You can do this by eliminating the need for the destructor (by not using a pointer: list<string> mEntries), or by adding the needed code to the copy constructor and operator= to make a deep copy of the list.
You only need to do
list<string> entries;
entries.push_back();
You do not need to create a pointer to entries.
Nothing too obvious, though you typed
mEntries->push_back(string(entryData));
and I htink you meant entry instead of entryData. You also don't need the string conversion on that line, and your function should take entry by const reference.
However, none of these things would cause your program to segfault. What compiler are you using?
You're missing the copy constructor. If the Logger object is copied and the original deleted, you'll be dereferencing memory that was previously deleted.
A simplified example of the problem
Logger a;
{
Logger b;
a=b;
}
a.WriteEntry("Testing");
Add a copy constructor.
Logger(const Logger& item)
{
mEntries = new list<string>();
std::copy(item.mEntries->begin(), item.mEntries->end(), std::back_inserter(*mEntries));
}