is it possible to pass to a function a whole class?

[wesdom]

i have a class that has N objects and i wanna pass all of them to a function that will binary search one number.. is it possible?
for example :

class book{
private:
int num;
};
int main()
{
book *b;
cin <<N;
b=new book[N];

}
void binary search(//i wanna pass the whole class here with all //objects in order to binary search them);

[Elysia]

Sure. Easiest way is to a vector or array:

std::vector<book> v(N); // If N is only known at runtime
binary_search(v);
void binary_search(const std::vector<book>& input);

std::array<book, N> v; // If N is known at compile time
binary_search(v);
void binary_search(const std::array<book, N>& input);

In either case, you can use .begin() and .end() to iterate over the array/vector. .size() gives you the size.
There is no need to use new.

[wesdom]

so i cant find the solution yet so i will upload a part of my code if sb can help me more .... when i put vector it says that does not name a type in namespace std...

class book{
private:
    string name;
    string author;
    int year;
    int price;
public:
    //book(string,string,int,int);
    void setall(string,string,int,int);
    void display();
    int price1(){return price;}

};
void book::setall(string str1,string str2,int p1,int p2)
{
    name=str1;
    author=str2;
    year=p1;
    price=p2;
}
void book::display()
{
    cout << "name : "  << name << "   author :  " << author << "   year :  "  << year << " price: "<<price<<endl;
     }

void binary_search(const std::vector<book>& S,int *,int,int);

int main()
{
int result;
int N;
string str1,str2;
  int p1,p2;
  int i=0;
  book *b=new book[N];
  ifstream myfile ("book.txt");
  if (myfile.is_open())
  {
    while ( myfile.good() )
    {
    if (i==0)
        myfile >> N;
    else {
      myfile >> str1 >> str2 >> p1 >> p2;
      //cout << "str1 : "  << str1 << "   str2 :  " << str2 << "   p1 :  "  << p1 << " p2: "<<p2<<endl;


    b[i-1].setall(str1,str2,p1,p2);}
    i++;
    }
    myfile.close();
  }
  int x;
std::vector<book> v(N);

binary_search(v,&result,N, x);


cout <<result<<endl;

if (result!=0)
    cout<<"It has been found at the position : "<<result;
else cout<<"there is no such element";

system("pause");
}

void binary_search(const std::vector<book>& S,int *result,int N,int keynum){
int mid;
int high=N-1;
int low=0;


do
{
mid= (low + high) / 2;
if ( keynum < S[mid].price1() )
high = mid - 1;
else if ( keynum > S[mid].price1())
low = mid + 1;
} while( keynum!=S[mid].price1() && low <= high);

if( keynum == S[mid].price1() )
{
//cout<<"It has been found at the position : "<<mid+1;
*result= mid+1;
}
else
{
*result=0;
}
system("Pause");

}

[laserlight]

when i put vector it says that does not name a type in namespace std...

You should #include <vector> to use std::vector.

[Elysia]

when i put vector it says that does not name a type in namespace std...

That typically means "you forgot to include the header for this type."
What is the appropriate header, then, you ask? For that, you refer to the documentation. cppreference.com is a good place to look.

[wesdom]

yea i saw all of them i include vector but i still cant use all of my objects like this

void binary_search(const std::vector<book>& S,int *result,int N,int keynum){
int mid;
int high=N-1;
int low=0;
for(int i =0; i<N; i++ )
    S[i].display();

/*do
{
mid= (low + high) / 2;
if ( keynum < S[mid].price1() )
high = mid - 1;
else if ( keynum > S[mid].price1())
low = mid + 1;
} while( keynum!=S[mid].price1() && low <= high);

if( keynum == S[mid].price1() )
{
//cout<<"It has been found at the position : "<<mid+1;
*result= mid+1;
}
else
{
*result=0;
}
system("Pause");*/

}

[Elysia]

Yes, you can. And again, you don't need to pass the size (and should not), because you can query the vector for it.
If it doesn't work, then show us the errors and the faulting code.

[wesdom]

im working on it i will let you know soon thenx a lot

[wesdom]

when i do somthing like this in my binary search S.display();
it says
|error: 'const class std::vector<book>' has no member named 'display'|
thats why i said i still cannt use all of my data because
a) i have this function in my class
and b) when i type S[i].display(); it prints this error:
error: passing 'const book' as 'this' argument of 'void book::display()' discards qualifiers [-fpermissive]|
so .... if you have any idea...

[phantomotap]

O_o

A member function which doesn't modify an instance of the class should be marked `const'.

The concept is called "const correctness" which is crucial in good C++ code.

I'd post a quick example, but you need more details than I have time. I'd suggest reading some tutorials.

Soma

[wesdom]

yea that's what i am up to wright now

[wesdom]

i saw some tutorials about const correctness and ... i realize that may i have not made clear whats my goal. i dont need to pass to a function a const object ,i ned to pass to my function a table of objects....
in order to explain this a litle bit here is an example
my class will look like this

class book{
private:
    string name;
    string author;
    int year;
    int price;
}

and i want to do a binary search for N objects inside my function for the price till i fount much through different objects price
i hope i have make a litle bit more understandable...
i dont think i need to const my values since i want to be able to change them

[MutantJohn]

The concept is called "const correctness" which is crucial in good C++ code.

And C too!

Doesn't it also allow the compiler to further optimize code? Or is that just an urban legend?

[Elysia]

i hope i have make a litle bit more understandable...

Nope. You're not making any sense.

i dont think i need to const my values since i want to be able to change them

binary_search does not need to--and should not--modify its arguments. That's why we pass it by const reference. That means you need to make member functions that do not change the object's state const.

[wesdom]

yea but even if i put const my values i still wont be able to do the search over all my objects ... it sure has to be a way to process all my class objects through my search function this is what is my final goal