I have a problem when accessing the overflowed square bracket in a public method of my class. Here is the code:
#include <iostream>
#include <cassert>
#include <cmath>
using namespace std;
template<unsigned int DIM> class Vector
{
private:
double mData[DIM];
public:
Vector(double tableau[DIM])
{
for(int i=0; i<DIM; i++)
{
mData[i] = tableau[i];
}
}
double operator[](int index)
{
assert(index < DIM);
assert(index > -1);
assert(-pow(10,-6)<=mData[index]<=1+pow(10,-6));
if(mData[index]>=0 && mData[index]<=1)
{
return mData[index];
}
else if(mData[index]<0 && mData[index]>=pow(10,-6))
{
return 0.0;
}
else if(mData[index]>1 && mData[index]<= 1+ pow(10,-6))
{
return 1.0;
}
}
double getDim() const
{
return DIM;
}
void print() const
{
for(int i=0;i<getDim();i++)
{
cout << this[i] << " "; //PROBLEM!!
}
}
};
int main()
{
double err=pow(10,-6);
double tableau[5];
tableau[0] = 0.5;
tableau[1] = 0.79;
tableau[2] = err;
tableau[3] = 1+err;
tableau[4] = 0;
Vector<5> proba(tableau);
proba.print();
}
I have tried with *this, this->, but anything appeared to work.
I hope you could help me.
Florent
Member operator overloads require a value or reference of the class type, and this is a pointer. So you either need to dereference the this pointer prior to using the operator, like this:
(*this)[i]
Or you can call the operator directly, which has the advantage of being totally explicit in its intent, but has the disadvantage of being a bit wordy and a bit more obscure (and therefore more likely to trip up anyone who reads it):
this->operator[](i)
If you have already tried *this[i] and found that it doesn't fix the problem, that's because it actually means *(this[i])!
Apart from wrong implementation of operator[], there is wrong use of it:-
cout << this[i] << " ";
This should be
cout << (*this)[i] << " "; //is you want to implement that way...
this is just a pointer, so to access operator[] you can either dereference it first:
cout << (*this)[i] << " ";
Or call the function directly (not preferred):
cout << this->operator[](i) << " ";
Related
As an exercise, I'm trying to create a class myArray that acts as a simplified array class. Here is my header:
#ifndef myArray_h
#define myArray_h
typedef double ARRAY_ELEMENT_TYPE;
class myArray {
public:
//--constructors
myArray(int initMax);
// post: Allocate memory during pass by value
myArray(const myArray & source);
// post: Dynamically allocate memory during pass by value
//--destructor
~myArray();
// post: Memory allocated for my_data is deallocated.
//--modifier
void set(int subscript, ARRAY_ELEMENT_TYPE value);
// post: x[subscript] = value when subscript is in range.
// If not, an error message is displayed.
//--accessor
ARRAY_ELEMENT_TYPE sub(int subscript) const;
// post: x[subscript] is returned when subscript is in range.
// If not, display an error message and return [0].
private:
ARRAY_ELEMENT_TYPE* my_data;
int my_capacity;
};
#endif
Here is my implementation:
#include "myArray.h"
#include <iostream>
#include <cstring>
using namespace std;
typedef double ARRAY_ELEMENT_TYPE;
//--constructors
myArray::myArray(int initMax)
{
my_capacity = initMax;
}
myArray::myArray(const myArray & source)
{
int i;
my_data = new ARRAY_ELEMENT_TYPE[source.my_capacity];
for(i=0; i < my_capacity; i++)
my_data[i] = source.sub(i);
}
//--destructor
myArray::~myArray()
{
delete [ ] my_data;
}
//--modifier
void myArray::set(int subscript, ARRAY_ELEMENT_TYPE value)
{
if(subscript > my_capacity - 1)
{
cout << "**Error: subscript " << subscript << " not in range 0.." << my_capacity-1 << ". The array is unchanged." << endl;
}
else
my_data[subscript] = value;
}
//--accessor
ARRAY_ELEMENT_TYPE myArray::sub(int subscript) const
{
if(subscript >= my_capacity)
{
cout << "**Error: subscript " << subscript << " not in range 0.." << my_capacity-1 << ". Returning first element." << endl;
cout << my_data[0];
}
else
{
return my_data[subscript];
}
}
And I'm using this as a test driver:
#include <iostream>
using namespace std;
typedef double ARRAY_ELEMENT_TYPE;
#include "myArray.h"
void show (const myArray & arrayCopy, int n)
{
for(int j = 0; j < n; j++)
cout << arrayCopy.sub(j) << endl;
}
int main()
{
int n = 6;
myArray a(6);
a.set(0, 1.1);
a.set(1, 2.2);
a.set(2, 3.3);
a.set(3, 4.4);
a.set(4, 5.5);
a.set(5, 6.6);
show(a, n);
cout << a.sub(11) << endl;
a.set(-1, -1.1);
return 0;
}
The problem is that when I run this, I get nothing for a bit, then the "Press any key to continue..." prompt. What's going wrong?
The myArray constructor doesn't allocate memory for my_data. The first time you call set, it attempts to write to an uninitialised pointer. This results in undefined behaviour but a crash is likely.
You should change the constructor to
myArray::myArray(int initMax)
{
my_capacity = initMax;
my_data = new ARRAY_ELEMENT_TYPE[my_capacity];
}
There are a couple of other issues with the code you could also consider
In 'set', the test
if(subscript > my_capacity - 1)
should be
if(subscript < 0 || subscript > my_capacity - 1)
Or you could change the subscript argument to have type unsigned int.
In sub, the line cout << my_data[0]; should presumably be return my_data[0];
myArray::myArray(int initMax)
{
my_capacity = initMax;
my_data = new ARRAY_ELEMENT_TYPE[my_capacity]; //You missed this
}
In addition to missing your allocation in your current implementation, you are also dynamically allocating memory. A simple array type does not need to be allocated on the heap. The std::array collection does exactly what you are looking to do. I would urge you to look at its implementation for an example (if this is just an academic exercise). If this is for a production codebase, use what is already written and tested.
http://en.cppreference.com/w/cpp/container/array
I've been trying to use a hash_multimap for sometime now, but the find method keeps giving me a iterator to the end of the container even though I know it found a matching key. What has me confused is that I've used the same code before for a different project with it working perfectly but now its playing up. The reason I know its finding something is because I've put a few cout in the hash function and hash compare, which is telling me that a key is found and that it matches what I gave the hash_multimap::find meathod, yet still it gives me an iterator.
first the header file
//
// HashGrid.h
// Planetarium
//
// Created by Taura J Greig on 24/08/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//
#ifndef _HASHGRID_
#define _HASHGRID_
#include <iostream>
#include <hash_map>
#include <deque>
#include "..//hashKey.h"
struct myTraits
{
static const size_t bucket_size = 4;
static const size_t min_buckets = 8;
myTraits() { };
myHash hashfunction;
myEqualTo equal_to;
size_t operator() (const hashKey& key) const
{
size_t hashval = 0;
hashval = ((key.y * globalGridWidth) + key.x);
cout << "x : " << key.x << " y : " << key.y << endl;
cout << "hashVal : " << hashval << endl;
return hashval;
}
bool operator() (const hashKey& key1, const hashKey& key2) const
{
bool test = (key1.x == key2.x && key1.y == key2.y);
cout << "equal_to = " << test << endl;
return test;
}
};
using namespace std;
//using namespace stdext;
using namespace stdext;
template <class T>
class HashGrid
{
public:
typedef deque<T *> localObjects;
typedef pair<hashKey, T *> addingPair;
typedef hash_multimap <hashKey, T *, myTraits> hashmMap;
typedef typename hash_multimap <hashKey, T *, myTraits> :: iterator hashmMapItor;
typedef pair<hashmMapItor, hashmMapItor> valueRange;
private:
hashKey keyOffsets[9];
int gridSize;
hash_multimap<hashKey, T*, myTraits> theMap;
inline bool exists(hashKey & theKey);
inline bool exists(hashKey & theKey, hashmMapItor & it);
public:
HashGrid();
void setup(int gridSize);
void update();
void draw(); // this is used for viusal debug,
void resize();
void addObject(T * object);
void getLocalObjects(float & x, float & y, int range, localObjects & p1);
};
template <class T>
inline bool HashGrid<T>::exists(hashKey & theKey)
{
hashmMapItor it;
it = theMap.find(theKey);
if (it == theMap.end())
{
return false;
}
else
{
return true;
}
}
template <class T>
inline bool HashGrid<T>::exists(hashKey & theKey,
hashmMapItor & it)
{
it = theMap.find(theKey);
if (it == theMap.end())
{
return false;
}
else
{
return true;
}
}
#include "HashGrid.cpp"
#endif
and the source file
//
// HashGrid.cpp
// Planetarium
//
// Created by Taura J Greig on 26/08/12.
// Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//
#ifndef _HASHGRID_SOURCE_
#define _HASHGRID_SOURCE_
#include "HashGrid.h"
#include "ofMain.h"
template<class T>
void HashGrid<T>::update()
{
theMap.clear();
}
template <class T>
void HashGrid<T>::addObject(T *obj)
{
hashKey tempKey;
tempKey.x = int(obj -> getPos().x) / gridSize;
tempKey.y = int(obj -> getPos().y) / gridSize;
cout << "tempKey.x : " << tempKey.x << endl;
cout << "tempKey.y : " << tempKey.y << endl;
theMap.insert(addingPair(tempKey, obj));
}
template <class T>
void HashGrid<T>::getLocalObjects(float & x, float & y, int range, localObjects & p1)
{
cout << "you are gettin local objects" << endl;
int gridX = (int(x) / gridSize);
int gridY = (int(y) / gridSize);
cout << "player x : " << x << endl;
cout << "player y : " << y << endl;
cout << "girdX " << gridX << endl;
cout << "girdY " << gridY << endl;
for (int i = 0; i < 9; i++)
{
hashKey tempkey;
tempkey.x = gridX;
tempkey.y = gridY;
tempkey += keyOffsets[i];
cout << i << " tempKey : " << tempkey.x << " " << tempkey.y << endl;
cout << "exists " << exists(tempkey) << " ";
//this is where the problem lies, the exists function will always return
//false even when the key is found
if (exists(tempkey))
{
cout << "found" << endl;
hashmMapItor it;
valueRange elements;
elements = theMap.equal_range(tempkey);
for (it = elements.first; it != elements.second; it++)
{
p1.push_back(it->second);
}
}
else
{
cout << "not found" << endl;
}
}
}
#endif
Note that I've cut a lot of methods out of the block above to save space because they are unrelated to the problem at hand. However I've left their declarations in the header file. Also I am aware that there a few things that I'm doing with templates that are ugly. Just deal with it for now.
Now I'll go into detail about whats happening in the code and where the problem lies. In the getlocalobjects method, the method "exists(key)" is called to determine if the hash_multimap has an element with the key provided. I know that it does find something because as I mentioned above because I put cout in the equal_to function to tell me when its used an what its result are.
Consistently its telling me yes (via equal_to debug) it found something but the exist method will still return false. This leading me to believe that there may be a bug in hash_multimap::find since it means that even if it finds something its gives me an iterator to hash_multimap::end
So my question is am I doing horribly wrong regarding the use of the multimap? does my traits struct not have something required for the multimap to work correctly
EDIT and the implementation for the hashKey that i forgot it include
header
#ifndef _HASHKEY_
#define _HASHKEY_
#include <iostream>
using namespace std;
static int globalGridSize = 1;
static int globalGridWidth = 1;
static int globalGridHeight = 1;
struct hashKey
{
public:
int x;
int y;
hashKey();
hashKey(int x, int y);
void set(int x, int y);
void set(hashKey & key);
void printKey()
{
cout << x << " " << y << endl;
}
bool operator < (const hashKey & key1) const;
bool operator == (const hashKey & key1) const;
hashKey& operator += (hashKey & key1);
};
#endif
and source
#ifndef _HASHKEY_SOURCE_
#define _HASHKEY_SOURCE_
#include "hashKey.h"
hashKey::hashKey()
{
x = 0;
y = 0;
}
hashKey::hashKey(int x, int y)
{
hashKey::x = x;
hashKey::y = y;
}
void hashKey::set(int x, int y)
{
hashKey::x = x;
hashKey::y = y;
}
void hashKey::set(hashKey &key)
{
x = key.x;
y = key.y;
cout << "set: x = " << x << " y = " << y << endl;
}
bool hashKey::operator<(const hashKey &key1) const
{
if ( (this->x < key1.x) && (this->y < key1.y))
{
return true;
}
return false;
}
bool hashKey::operator == (const hashKey &key1) const
{
if ((this-> x == key1.x) && (this->y == key1.y))
{
return true;
}
return false;
}
hashKey& hashKey::operator+=(hashKey &key1)
{
this->x += key1.x;
this->y += key1.y;
return *this;
}
#endif
EDIT [SOVLED] I changed the hash_multimap tp an unordered_multimap and now it works, so initial suspicion was right, that at this time the hash_multimap is bugged an its find method will always give an iterator to the the end. Note that i'm using visual studio c++ 2010, it may not be bugged on other platforms or other compilers, however it defiantly was bugged in my case
The content below is speculation as not all the relevant code is visible.
It seems that you have:
A hash which is of type size_t (as created from the first operator() of myTraits)
A key of type hashKey (which is not a hash from the hash_multimap's perspective)
You did not provide the implementation of hashKey, so my immediate question is:
Did you provide the equality operator for hashKey?
Or alternatively, did you override equal_to<haskHey>?
The potential problem (and reason for the above questions) that I see is that you defined your hashmMap as hash_multimap <hashKey, T *, myTraits> which overrides the hashing function, but it does not override the key equality (which is of type hashKey). So, I presume that the default comparator of hashKey (and not the one defined in myTraits) might be used.
Perhaps hash_multimap <hashKey, T *, myTraits, myTraits> would suffice?
Update: I just notice that VS's hash_multimap has a different signature, than the one coming from STL. Compare:
Visual Studio version
STL version
The latter has hashing function and key comparator separated. This is just asking for terrible problems once you switch compilers!
I have requirement as follows.
I have to generate increment negative numbers from -1 to -100 which is used a unique id for a request. Like it should be like this: -1, -2, -3, ...-100, -1, -2, and so on. How can I do this effectively? I am not supposed to use Boost. C++ STL is fine. I prefer to write simple function like int GetNextID() and it should generate ID. Request sample program on how to do this effectively?
Thanks for your time and help
int ID = -1;
auto getnext = [=] mutable {
if (ID == -100) ID = -1;
return ID--;
};
Fairly basic stuff here, really. If you have to ask somebody on the Interwebs to write this program for you, you should really consider finding some educational material in C++.
I love the functor solution:
template <int limit> class NegativeNumber
{
public:
NegativeNumber() : current(0) {};
int operator()()
{
return -(1 + (current++ % limit));
};
private:
int current;
};
Then, you can define any generator with any limit and use it:
NegativeNumber<5> five;
NegativeNumber<2> two;
for (int x = 0; x < 20; ++x)
std::cout << "limit five: " << five() << "\tlimit two: " << two() << '\n';
You can also pass the generator as parameter to another function, with each funtor with its own state:
void f5(NegativeNumber<5> &n)
{
std::cout << "limit five: " << n() << '\n';
}
void f2(NegativeNumber<2> &n)
{
std::cout << "limit two: " << n() << '\n';
}
f5(five);
f2(two);
If you don't like the template solution to declare the limit, there's also the no-template version:
class NegativeNumberNoTemplate
{
public:
NegativeNumberNoTemplate(int limit) : m_limit(limit), current(0) {};
int operator()()
{
return -(1 + (current++ % m_limit));
};
private:
const int m_limit;
int current;
};
Using as argument to a function works in the same way, and it's internal state is transfered as well:
void f(NegativeNumberNoTemplate &n)
{
std::cout << "no template: " << n() << '\n';
}
NegativeNumberNoTemplate notemplate(3);
f(notemplate);
I hope you don't want to use it with threading, they're not thread safe ;)
Here you have all the examples; hope it helps.
Something like.... (haven't compiled)
class myClass
{
int number = 0;
int GetValue ()
{
return - (number = ((number+1) % 101))
}
}
Even a simple problem like this could lead you to several approximations, both in the algorithmic solution and in the concrete usage of the programming language.
This was my first solution using C++03. I preferred to switch the sign after computing the value.
#include <iostream>
int GetNextID() {
// This variable is private to this function. Be careful of not calling it
// from multiple threads!
static int current_value = 0;
const int MAX_CYCLE_VALUE = 100;
return - (current_value++ % MAX_CYCLE_VALUE) - 1;
}
int main()
{
const int TOTAL_GETS = 500;
for (int i = 0; i < TOTAL_GETS; ++i)
std::cout << GetNextID() << std::endl;
}
A different solution taking into account that the integer modulo in C++ takes the sign of the dividend (!) as commented in the Wikipedia
#include <iostream>
int GetNextID() {
// This variable is private to this function. Be careful of not calling it
// from multiple threads!
static int current_value = 0;
const int MAX_CYCLE_VALUE = 10;
return (current_value-- % MAX_CYCLE_VALUE) - 1;
}
int main()
{
const int TOTAL_GETS = 50;
for (int i = 0; i < TOTAL_GETS; ++i)
std::cout << GetNextID() << std::endl;
}
#include <iostream>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <vector>
using namespace std;
struct delete_ptr
{
template<typename T>
void operator()(T*& t)
{
delete t;
t = 0;
}
};
struct is_null_ptr
{
template<typename T>
bool operator()(T*& t)
{
return t == 0;
}
};
struct A
{
static void removeDead(A*& a)
{
if(a and a->dead)
delete_ptr()(a);
}
static void killSome(A* a)
{
if(a and a->isDead() == false and rand()%100 == 0)
{
static int counter = 0;
cout << "Kill___" << ++counter << endl;
a->kill();
}
}
static void reviveSome(A* a)
{
if(a and a->isDead() and rand()%3 == 0)
{
static int counter = 0;
cout << "Revive___" << ++counter << endl;
a->revive();
}
}
A():dead(false)
{
}
virtual ~A()
{
static int counter = 0;
cout << "Dtor___" << ++counter << endl;
}
bool isDead(){return dead;}
void kill(){dead = true;}
void revive(){dead = false;}
bool dead;
};
int main()
{
srand(time(0));
vector<A*> as;
for(int i = 0; i < 200; ++i)
{
A* a = new A;
as.push_back(a);
}
for_each(as.begin(),as.end(),A::killSome);
for_each(as.begin(),as.end(),A::reviveSome);
for_each(as.begin(),as.end(),A::removeDead);
as.erase( std::remove_if(as.begin(),as.end(),is_null_ptr()),as.end());
cout << as.size() << endl;
for_each(as.begin(),as.end(),delete_ptr());
as.clear();
return 0;
}
It allocates them, and prints the right output but I'm not sure this is the right thing I'm doing. I was just trying to use pointers in a vector and delete them when a certain condition happens, without using boost or c++11.
So what do you think about it?
Since the only smart pointer present in the current STL (auto_ptr) cannot be used in containers, I would say your way is a good one under the given conditions.
You could think about implementing your own unique_ptr or shared_ptr however.
PS: There are many reasons to use pointers instead of the actual objects in a container, one is polymorphism. Another one is that the actual objects are already stored somewhere else (think of an index structure to already stored objects).
I am trying ot add a function template that will print if it contains precision values or valves and the value. The rest of the program works except this function. I am not sure what I am doing wrong but the error I recieve is:
error C2784: 'void printInstrumentDetail(const I *const )' : could not deduce template argument for 'const I *const ' from 'std::vector<_Ty>'
#include <iostream>
#include <vector>
#include <iomanip>
#include <string>
#include "Instruments.h"
#include "Brass.h"
#include "Strings.h"
using namespace std;
//template<typename I> <---Problem
//void printInstrumentDetail(const I * const a)
//{
// for (size_t i = 0; i < 6; i ++)
// {
// cout << "The details for " << a[i]->getName()
// << ": " << a[i]->print();
// }
//}
int main()
{
double total = 0;
Strings violin("Violin", 553.90, 3);
Strings cello("Cello", 876.45, 3);
Strings viola("Viola", 200.50, 23);
Brass tuba("Tuba", 1400.10, 1.23);
Brass trumpet("Trumpet", 500.00, 4.32);
Brass sax("Sax", 674.78, .99);
vector <Instruments *> band(6);
band[0] = &violin;
band[1] = &tuba;
band[2] = &cello;
band[3] = &trumpet;
band[4] = &viola;
band[5] = &sax;
cout << fixed << setprecision(2);
cout << "The instruments in the band are:\n";
//Get name and cost of each
for (size_t i = 0; i < 6; i ++)
{
cout << band[i]->getName() << " $"
<< band[i]->getCost() << endl;
}
cout << "\nThen band is warming up..." << endl;
//Get descrition of how sound is made of each
for (size_t i = 0; i < 6; i ++)
{
cout << "This " << band[i]->getName()
<< " makes sounds by " ;
band[i]->playSound();
}
cout << "\nTotal cost of the band is: $" ;
//Get total cost of all instruments
for (size_t i = 0; i < 6; i ++)
{
total = band[i]->getCost() + total;
}
cout << total << endl;
//printInstrumentDetail(band); <--Problem
return 0;
}
Here's the base class:
#ifndef INSTRUMENTS_H
#define INSTRUMENTS_H
#include <string>
using namespace std;
class Instruments
{
public:
Instruments(string, double);
void setName(string);
virtual string getName();
void setCost(double);
virtual double getCost();
virtual void print();
virtual void playSound();
private:
string name;
double cost;
};
#endif
#include <iostream>
#include "Instruments.h"
using namespace std;
Instruments::Instruments(string n, double c)
{
name = n;
cost = c;
}
void Instruments::setName(string n)
{
name = n;
}
string Instruments::getName()
{
return name;
}
void Instruments::setCost(double c)
{
cost = c;
}
double Instruments::getCost()
{
return cost;
}
void Instruments::print()
{
}
void Instruments::playSound()
{
//empty
}
Derived class Bass:
#ifndef BRASS_H
#define BRASS_H
#include <string>
#include "Instruments.h"
using namespace std;
class Brass : public Instruments
{
public:
Brass(string, double, double);
void setPrecisionValue(double);
double getPrecisionValue();
void print() ;
void playSound();
private:
double precision;
string sound;
};
#endif
#include <iostream>
#include "Brass.h"
using namespace std;
Brass::Brass(string n, double c, double p)
:Instruments(n, c)
{
precision = p;
}
void Brass::setPrecisionValue(double p)
{
precision = p;
}
double Brass::getPrecisionValue()
{
return precision;
}
void Brass::print()
{
cout << getPrecisionValue() << endl;
}
void Brass::playSound()
{
cout << "blowing in a mouthpiece." << endl;
Instruments::playSound();
}
Derived class Strings:
#ifndef STRINGS_H
#define STRINGS_H
#include <string>
#include "Instruments.h"
using namespace std;
class Strings : public Instruments
{
public:
Strings(string, double, int);
void setValves(int);
int getValves();
void print();
void playSound();
private:
int valves;
};
#endif
#include <iostream>
#include "Strings.h"
using namespace std;
Strings::Strings(string n, double c, int v)
:Instruments(n, c)
{
valves = v;
}
void Strings::setValves(int v)
{
valves = v;
}
int Strings::getValves()
{
return valves;
}
void Strings::print()
{
cout<< getValves() << endl;
}
void Strings::playSound()
{
cout << "striking with a bow." << endl;
Instruments::playSound();
}
Well, the problem is that your template requires a pointer:
template<typename I>
void printInstrumentDetail(const I * const a);
but you're giving it a vector, not a pointer:
vector <Instruments *> band(6);
...
printInstrumentDetail(band);
You can hack your way around this by passing a pointer to the printInstrumentDetail function, like so:
printInstrumentDetail(&band[0]);
But really, you'd be much better off modifying printInstrumentDetail to take a container or a pair of iterators:
template <typename ContainerT>
void printInstrumentDetail(const ContainerT& a)
or
template <typename IteratorT>
void printInstrumentDetail(IteratorT first, IteratorT last)
with the appropriate modifications to the definition of the function.
Pass the pointer to vector
printInstrumentDetail(&band);
and inside printInstrumentDetail
(*a)[i]->getName();
Well, first off I don't believe you can pass a vector as a const * I const at
printInstrumentDetail(band);
Vector cannot be just cast to a pointer. One working solution would be something like:
template <typename T>
void printInstrumentDetail( const std::vector<T*>& band )
{
for ( size_t i = 0; i < band.size(); ++i )
cout << "The details for " << band[i]->getName()
<< ": " << band[i]->print();
}
And there are many others, including iterators, functors, STL algorithms, etc.
You are trying to pass an object to an interface that wants a pointer.
void printInstrumentDetail(const I * const a)
Convert this to a reference.
void printInstrumentDetail(I const I& a)
But to conform to the pattern that is common in C++. You should pass the beginning and end of the sequence as parameters. ie change your function to take itertors rather than a pointer.
Instead of passing the pointer:
printInstrumentDetail(const I * const a)
you can pass the reference:
printInstrumentDetail(const I& a)
Everything else stays unchanged.
First of all, there seems to be no reason for PrintInstrumentDetail to be a template at all -- it works with pointers to the base class, and unless you're likely to have other types with getName() and print() members to which it might be applied, it can/could/should just work with pointers to the base class.
Second, I'd think hard about changing how you do the job. Instead of a member function in each Instrument, and PrintInstrumentDetail to loop over all the instruments, I'd think hard about defining operator<< for Instrument, and using a standard algorithm to print out the details.
Looking at it, I think a few other things should change as well. First of all, unless you're dealing with really unusual instruments, the number of valves on a brass instrument is fixed forever -- so it should NOT have a SetValve() member. Rather, the number of valves should be set during construction, but not be open to change afterwards.
String instruments don't have valves at all (at least most normal ones don't), so they shouldn't have SetValves(), GetValves(), or anything else related to valves.
Likewise, unless you're doing something pretty unusual, the cost of an instrument can never change -- you paid what you paid, so the cost should be set during construction, and not open to later alteration.
Edit: one other thing: instead of hard-coding 6 everywhere, use band.size() to loop over all the instruments in the band.