How to optimize such simple data (event) casting Class? - c++

So I have created compilable prototype for a graph element that can cast its data to subscribed functions.
//You can compile it with no errors.
#include <iostream>
#include <vector>
using namespace std ;
class GraphElementPrototype {
// we should define prototype of functions that will be subscribers to our data
typedef void FuncCharPtr ( char *) ;
public:
//function for preparing class to work
void init()
{
sample = new char[5000];
}
// function for adding subscribers functions
void add (FuncCharPtr* f)
{
FuncVec.push_back (f) ;
} ;
// function for data update
void call()
{
// here would have been useful code for data update
//...
castData(sample);
} ;
//clean up init
void clean()
{
delete[] sample;
sample = 0;
}
private:
//private data object we use in "call" public class function
char* sample;
//Cast data to subscribers and clean up given pointer
void castData(char * data){
for (size_t i = 0 ; i < FuncVec.size() ; i++){
char * dataCopy = new char[strlen(data)];
memcpy (dataCopy,data,strlen(data));
FuncVec[i] (dataCopy) ;}
}
// vector to hold subscribed functions
vector<FuncCharPtr*> FuncVec ;
} ;
static void f0 (char * i) { cout << "f0" << endl; delete[] i; i=0; }
static void f1 (char * i) { cout << "f1" << endl; delete[] i; i=0; }
int main() {
GraphElementPrototype a ;
a.init();
a.add (f0) ;
a.add (f1) ;
for (int i = 0; i<50000; i++)
{
a.call() ;
}
a.clean();
cin.get();
}
Is it possible to optimize my data casting system? And if yes how to do it?

Implement the program correctly and safely
If performance Not Acceptable
While Not Acceptable
Profile
Optimize
Done!
In my experience, premature optimization is the devil.
EDIT:
Apparently while I was formatting my answer, another James ninja'd me with a similar answer. Well played.

Is it possible to optimize my data casting system? And if yes how to do it?
If your program is not too slow then there is no need to perform optimizations. If it is too slow, then generally, improving its performance should be done like so:
Profile your program
Identify the parts of your program that are the most expensive
Select from the parts found in step 2 those that are likely to be (relatively) easy to improve
Improve those parts of the code via refactoring, rewriting, or other techniques of your choosing
Repeat these steps until your program is no longer too slow.

Related

How to calculate the length of a mpz_class in bytes?

I want to implement RSA with padding but first I have to find out the length in bytes of the message which is a mpz_class item. Which function would be useful in cpp to accomplish this?
const mpz_class m(argv[1])
What is the length of m in bytes?
Thank you!
#Shawn's comment is correct: The bytes occupied in memory by your class are not what you should be concerned about. Not only does the location of the bytes in memory depend on how your compiler decides to pack them, but their order can also depend on the hardware used.
So, instead of doing some awkward and very fragile memcopy'ish thing that are almost guaranteed to break at some point, you should construct the message yourself (google keyword: Serialization). This also has the advantage that your class can contain stuff that you don't want to add to the message (caches with temp results, or other implementation/optimization stuff).
To the best of my knowledge C++ (unlike f.ex. C#) does not come with build in serialization support, but there are likely to exist libraries that can do a lot of it for you. Otherwise you just have to write your "data member to byte array" functions yourself.
Super simple example:
#include <vector>
#include<iostream>
class myClass
{
int32_t a;
public:
myClass(int32_t val) : a(val) {}
// Deserializer
bool initFromBytes(std::vector<uint8_t> msg)
{
if (msg.size() < 4)
return false;
a = 0;
for (int i = 0; i < 4; ++i)
{
a += msg[i] << (i * 8);
}
return true;
}
// Serializer
std::vector<uint8_t> toBytes()
{
std::vector<uint8_t> res;
for (int i = 0; i < 4; ++i)
{
res.push_back(a >> (i*8));
}
return res;
}
void print() { std::cout << "myClass: " << a << std::endl; }
};
int main()
{
myClass myC(123456789);
myC.print();
std::vector<uint8_t> message = myC.toBytes();
myClass recreate(0);
if (recreate.initFromBytes(message))
recreate.print();
else
std::cout << "Error" << std::endl;
return 0;
}

Array elements of a class object are not being set correctly, set() and get() member functions likely cause

This is my first time working with classes in C++ and I seem to be getting tripped up quite a lot. My program is supposed to be a rewrite of a previous program that used struct (see here: Random number generator in a for loop gives same numbers each time), but using a class instead.
#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
using namespace std;
const int WHEEL_POSITIONS = 30;
const char wheelSymbols[WHEEL_POSITIONS + 1] = "-X-X-X-X-X=X=X=X*X*X*X*X#X#X7X";
class slotMachine
{
private:
int spinPos;
char spinSymbol;
public:
slotMachine(); // Constructor
char symbols[WHEEL_POSITIONS + 1]; // Should be private?
void setSpinSymbol(); // Spins the wheels
char getSpinSymbol() const // Returns the symbol
{ return spinSymbol; }
} wheels[3];
// Constructor initializes slot wheels to contents of wheelSymbols
slotMachine::slotMachine()
{
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < (WHEEL_POSITIONS + 1); j++)
{
wheels[i].symbols[j] = wheelSymbols[j];
}
}
}
void slotMachine::setSpinSymbol()
{
for (int i = 0; i < 3; i++)
{
wheels[i].spinPos = (rand() % WHEEL_POSITIONS);
wheels[i].spinSymbol = wheels[i].symbols[(wheels[i].spinPos)];
}
}
void displayResults(slotMachine fwheels[3])
{
for (int i = 0; i < 3; i++)
{
cout << fwheels[i].getSpinSymbol();
}
}
void displayResults(slotMachine []);
//bool getWinner(slotMachine []);
int main(void)
{
slotMachine wheels[3];
time_t seed;
time(&seed);
srand(seed);
displayResults(wheels);
return 0;
}
The code compiles but outputs the following:
I have a feeling this error is caused by something having gone amiss in my constructor slotMachine, my getSpinSymbol() function, or my setSpinSymbol() function, but I've looked it over several times and can't seem to figure it out. I've read a handful of material online covering classes in C++, but I'm still very new and very shaky on the concept--apologies if it's something small or obvious that I've overlooked.
There are several issues with your code:
1.Class names should be started with upper case letter. slotMachine -> SlotMachine
2.Remove wheels[3] after class definition.You are using the array declared in main() method.
3.Why you are declaring displayResults(..) again after it's definition?
4.You are not calling setSpinSymbol() before displayResults(..).
The problem was explained to me by a friend not on StackOverflow, and I will transcribe his answer here in case anyone else (for any reason) runs into the same problem:
You aren't using constructors and methods correctly. You shouldn't be
accessing wheels (the array of slotMachine objects) directly inside
those methods; you should just be performing operations on "this," the
slotMachine object on which the method was called. For example, the
constructor slotMachine::slotMachine() is automatically called for
each element of the array wheels. You just need to initialize the
current slotMachine object inside the constructor:
slotMachine::slotMachine()
{
for (int j = 0; j < (WHEEL_POSITIONS + 1); j++)
{
this->symbols[j] = wheelSymbols[j];
}
}
And slotMachine::setSpinSymbol() should just set the value of
spinSymbol for the object on which the method was called:
void slotMachine::setSpinSymbol()
{
this->spinPos = (rand() % WHEEL_POSITIONS);
this->spinSymbol = symbols[this->spinPos];
}
(In all of this code, the this-> part is actually unnecessary; you
can leave it out if you want. I put it in to try to make it clearer
that these methods are operating on fields of "the current object.")
Now, the reason you are getting garbage is because you never call
setSpinSymbol(), so the spinSymbol field is never initialized in
these objects. You probably want to call setSpinSymbol() in the
constructor, so that the spinSymbol field is guaranteed to be
initialized.
This explanation did solve my problem, and my program now outputs the correct information, so I believe it to be correct. My issues with using constructors and methods correctly has been explained here, and the reason why I was getting garbage values (as well as a few other points) was answered by another commenter.

C++ Struct defined data passing. Simple answer im sure

I am sure this is a very simple fix and I feel dumb asking it but here it goes.
I need help with a struct and passing info from a gather function to a save or set function, and then passing it again to another function for further use.
Basically, it looks like this to start. I'll just add short snips of the code. All can be provided if you would like to see it.
I right now am just looking for the proper way to pass struct defined data from get.... to set.... functions.
struct printype
{
char dots[8][15];
int unknown15; // can have values of 0..127
string serial11_14; // 8 characters 00000000...99999999
int year8; // without century, 0..99
int month7; // 1..12
int day6; // 1..31
int hour5; // 0..23
int minute2; // 0..59
};
int getunknown15(); // prototypes
int setunknown15(int);
then we have a simple main.
int main()
{
printype pt;
pt.unknown15=getunknown15();
pt.unknown15=setunknown15(12);
pt.serial11_14=getserial11_14();
pt.serial11_14=setserial11_14("12345678");
pt.year8=getyear8();
pt.year8=setyear8(44);
pt.month7=getmonth7();
pt.month7=setmonth7(11);
pt.day6=getday6();
pt.day6=setday6(12);
pt.hour5=gethour5();
pt.hour5=sethour5(12);
pt.minute2=getminute2();
pt.minute2=setminute2(23);
cout <<"-----------------------------------------------------"<<endl;
cout <<" Let's Get Started"<<endl;
cout <<"-----------------------------------------------------"<<endl;
setup(pt.dots); // sets up the array
dpinfo(pt); // prints out the final array
ftarray(pt);
spar(pt.dots);
darray(pt.dots);
}
and finally the get and set array functions.
int getunknown15()
{
printype tem;
cout <<"-----------------------------------------------------"<<endl;
cout <<" Enter the Unkown Variable (0-127): ";
cin >>tem.unknown15;
cout <<"-----------------------------------------------------"<<endl;
return tem.unknown15;
}
next is
int setunknown15(int tem)
{
printype pp;
if (tem>127||tem<0)
{
cout << "Error" << endl;
return 0;
}
else
{
pp.unknown15 = tem;
return pp.unknown15;
}
}
I hope this isn't too much to read and understand
Anyway, I know this has a really simple answer but my brain just isn't working right now.
Edit: As StilesCrisis stated, Send struct as parameter is quiet stupid in this case. better use a const reference.
Well, I am not sure if I understand your question correctly. You can simply send struct to another function as parameter, or as a pointer.
like:
void SetStruct(const printype& var);
printype GetStruct();
Is it what you are looking for?
Please use the following access to the your fields, (by reference):
struct printype *myPtr = new printype;
myPtr->day6 = 43;
When use pointer instead of a normal variable, you should use -> instead . to access your fields.
I know this is kind of old but I thought I should give it a shot, since you are using C++ and it looks like you are trying to use some OO practices (I think), you don't need to start with a struct, even though OO principles can be applied using them as well though not as elegantly.
you can define your class header file as such.
#ifndef PRINTYPE_H
#define PRINTYPE_H
#include <string>
using namespace std;
class printype
{
private: // we always want to declare our member fields private for safety/managements reasons, no one will be able to access them outside.
char dots[8][15];
int unknown15; // can have values of 0..127
string serial11_14; // 8 characters 00000000...99999999
int year8; // without century, 0..99
int month7; // 1..12
int day6; // 1..31
int hour5; // 0..23
int minute2; // 0..59
void init(); // This is the method we use to initialize our starting state.
public: // This is our public methods, how people deal with/get/set our state.
printype(); // This is our default constructor
printype(const printype& print_type); // This our copy constructor
virtual ~printype(); // This is our destructor, its virtual, making safer for inheritance.
// This is our setters/getters
void setUnknown(int unknown);
int getUnknown();
void setYear(int year);
int getYear();
void setMonth(int mont);
int getMonth();
// and well you get the idea, you can add more methods.
};
#endif
and the accompanying class source file with your functions implementation
printype::printype()
{
this->init(); // Initialize all your vatiables, safer to just define a function to this.
}
printype::printype(const printype& orig) // copy constructor
{
this->setUknown(orig.getUnknown());
this->setDay(orig.getDay());
this->setDots(orig.getDots());
// you get the idea ...
}
printype::~printype()
{
// Have anything you need to do before destroying the object.
}
void printype::init()
{
this->setUnknwon(0);
this->setyear(0);
this->setMonth(1);
char dots[8][15] = {'\0'};
this->setDots(dots);
// you get the idea, you want to initialize all your variables since, for the most part they initially hold garbage.
}
void printype::setUnknown(int unknown)
{
if (unknown >= 0 && unknown < 127)
this->unknown15 = unknown;
else
error("Expecting unknown to be between 0 and 127"); // error should probably print the error and/or exit(-1) up to u
}
int printype::setYear(int year)
{
if (year >= 1 && year <= 99)
this->year8 = year;
else
error("Expecting year between 0 and 99"); // you may want to implement an error function!
}
int printype::getYear()
{
return this->year8;
}
void printype::setDots(char dots[8][15])
{
// you may want to do some verifications
memcpy(this->dots, dots, sizeof(dots));
}
void printype::setDots(char **dots) // this is a bit unsafe, use at your own risk.
{
if (dots)
{
unsigned int index = 0;
for (index = 0; index < 8; index++)
if (dots[index])
memcpy(this->dots[index], dots[index], 15);
else
error("dots required pointer ...");
}
else
error("dots required pointer ...");
}
char **getDots() // We will be returning a copy, we don't want the internal state to be affected, from outside, by using reference or pointers.
{
char **dots = new char*[8];
unsigned int index = 0;
for (index = 0; index < 8; index++)
{
dots[index] = new char[15];
memcpy(dots[index], this->dots[index], 15);
}
return dots;
}
// and well you get the idea ...
to use your class
printype *print_type_p = new print_type();
// or
printype pront_type_p();
// use the different public method to update the internal state.
print_type_p->setYear(3);
// or
print_type.setYear(3);
print_type_p->getYear();
// and so on.

STL container leak

I'm using a vector container to hold instances of an object which contain 3 ints and 2 std::strings, this is created on the stack and populated from a function in another class but running the app through deleaker shows that the std::strings from the object are all leaked. Here's the code:
// Populator function:
void PopulatorClass::populate(std::vector<MyClass>& list) {
// m_MainList contains a list of pointers to the master objects
for( std::vector<MyClass*>::iterator it = m_MainList.begin(); it != m_MainList.end(); it++ ) {
list.push_back(**it);
}
}
// Class definition
class MyClass {
private:
std::string m_Name;
std::string m_Description;
int m_nType;
int m_nCategory;
int m_nSubCategory;
};
// Code causing the problem:
std::vector<MyClass> list;
PopulatorClass.populate(list);
When this is run through deleaker the leaked memory is in the allocator for the std::string classes.
I'm using Visual Studio 2010 (CRT).
Is there anything special I need to do to make the strings delete properly when unwinding the stack and deleting the vector?
Thanks,
J
May be Memory leak with std::vector<std::string> or something like this.
Every time you got a problem with the STL implementation doing something strange or wrong like a memory leak, try this :
Reproduce the most basic example of what you try to achieve. If it runs without a leak, then the problem is in the way you fill the data. It's the most probable source of problem (I mean your own code).
Not tested simple on-the-fly example for your specific problem :
#include <string>
#include <sstream>
// Class definition
struct MyClass { // struct for convenience
std::string m_Name;
std::string m_Description;
int m_nType;
int m_nCategory;
int m_nSubCategory;
};
// Prototype of populator function:
void populate(std::vector<MyClass>& list)
{
const int MAX_TYPE_IDX = 4;
const int MAX_CATEGORY_IDX = 8;
const int MAX_SUB_CATEGORY_IDX = 6;
for( int type_idx = 0; type_idx < MAX_TYPE_IDX ; ++type_idx)
for( int category_idx = 0; category_idx < MAX_CATEGORY_IDX ; ++category_idx)
for( int sub_category_idx = 0; sub_category_idx < MAX_SUB_CATEGORY_IDX ; ++sub_category_idx)
{
std::stringstream name_stream;
name_stream << "object_" << type_idx << "_" << category_idx << "_" << sub_category_idx ;
std::stringstream desc_stream;
desc_stream << "This is an object of the type N°" << type_idx << ".\n";
desc_stream << "It is of category N°" << category_idx << ",\n";
desc_stream << "and of sub-category N°" << category_idx << "!\n";
MyClass object;
object.m_Name = name_stream.str();
object.m_Description = desc_stream.str();
object.m_nType = type_idx;
m_nCategory =
m_nSubCategory =
list.push_back( object );
}
}
int main()
{
// Code causing the problem:
std::vector<MyClass> list;
populate(list);
// memory leak check?
return 0;
}
If you still got the memory leak, first check that it's not a false-positive from your leak detection software.
Then if it's not, google for memory leak problems with your STL implementation (most of the time on the compiler developer website). The implementor might provide a bug tracking tool where you could search in for the same problem and potential solution.
If you still can't find the source of the leak, maybe try to build your project with a different compiler (if you can) and see if it have the same effect. Again if the leak still occurs, the problem have a lot of chances to come from your code.
Probably same root issue as Alexey's link. The shipped version has broken move code for basic_string. MS abandoned us VC10 users, so you must fix it yourself. in xstring file you have this:
_Myt& assign(_Myt&& _Right)
{ // assign by moving _Right
if (this == &_Right)
;
else if (get_allocator() != _Right.get_allocator()
&& this->_BUF_SIZE <= _Right._Myres)
*this = _Right;
else
{ // not same, clear this and steal from _Right
_Tidy(true);
if (_Right._Myres < this->_BUF_SIZE)
_Traits::move(this->_Bx._Buf, _Right._Bx._Buf,
_Right._Mysize + 1);
else
{ // copy pointer
this->_Bx._Ptr = _Right._Bx._Ptr;
_Right._Bx._Ptr = 0;
}
this->_Mysize = _Right._Mysize;
this->_Myres = _Right._Myres;
_Right._Mysize = 0;
_Right._Myres = 0;
}
return (*this);
}
Note the last
_Right._Myres = 0;
that should happen only under the last condition, for the short case _Right should better be left alone.
As the capacity is set to 0 instead of 15, other code will take unintended branch in function Grow() when you assign another small string and will allocate a block of memory just to trample over the pointer with the immediate string content.

Segmentation Fault when trying to push a string to the back of a list

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));
}