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c++pointers
FourOfAKind
FourOfAKind

Reputation: 2418

Using explicit/raw pointers in c++

I read that using raw pointers in C++ is bad. Instead we should use auto_ptr. In the below code I am populating a vector in foo() that is created in the main(). Am I doing it right or is there a better way to do without using explicit pointers.

#include <iostream>
#include <vector>
#include <string>

using namespace std;

void foo(vector<string> *v){

    (*v).push_back(" hru");
}

int main(){
    vector<string> v;
    v.push_back("hi");
    foo(&v);
    for(int i=0;i<v.size(); i++){
        cout << v[i];
    }

}

Upvotes: 3

Views: 2706

Answers (3)

boto
boto

Reputation: 455

You can begin to think about using auto_ptr when you deal with objects created on heap (e.g. a class instance created by "new"). Your vector holds its elements by value, std::string elements it is. So you don't need to consider auto_ptr here at all. If your vector would hold instances created on heap then you could use something like this:

std::vector< auto_ptr< MyType > > vec;

auto_ptr< MyType > a( new MyType() );

vec.push_back( a );

and then when your vector elements get erased by e.g. your vec leaving its scope then instance 'a' will get deleted automatically.

With other words, auto_ptr is a kind of garbage collector which does a kind of automatic object deletion for you. See here for more information about auto_ptr http://www.cplusplus.com/reference/std/memory/auto_ptr

Upvotes: 0

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726549

C++ uses references for what you are trying to do:

#include <iostream>
#include <vector>
#include <string>

using namespace std;

void foo(vector<string>& v){
    v.push_back(" hru");
}

int main(){
    vector<string> v;
    v.push_back("hi");
    foo(v);
    for(int i=0;i<v.size(); i++){
        cout << v[i];
    }
}

References and pointers are similar, with one very important distinction: there is no such thing as a null reference (Constructing one is Undefined Behavior in C++ you can construct one, but doing so is considered a hack).

Upvotes: 4

Tudor
Tudor

Reputation: 62439

In C++ you can avoid the pointer and use a pass-by-reference:

#include <iostream>
#include <vector>
#include <string>

using namespace std;

void foo(vector<string>& v){

    v.push_back(" hru");
}

int main(){
    vector<string> v;
    v.push_back("hi");
    foo(v);
    for(int i=0;i<v.size(); i++){
        cout << v[i];
    }    
}

Upvotes: 3

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