access to a vector witout ->at() function;

[Ultras]

Hi all.
For example we have:
#include <iostream>
#include <vector>

using namespace std;
void myFunction(vector<int> *v);


int main(void){


vector<int> a;
a.push_back(10);
a.push_back(20);
a.push_back(30);
a.push_back(40);
myFunction(&a);

system("PAUSE");
}



void myFunction(vector<int> *v){
cout<<v->at(2); //will work but we cant use it...
cout<<v[2]; //error.
cout<<*v[2]; //error.
}
The question is how we can get acces to the elements of the vector *v ?
Using of iterators will be too slow in case of big vector.
Any other ways to solve it?

PS: is "->at()" function using iterators i.e its not a random acces DS.

[mf]

You can use cout<<(*v)[2], or:

Code: Select all

void myFunction(vector<int> &v){
   cout<<v.at(2);
   cout<<v[2];
} 

[Ultras]

cout<<(*v)[2]
its working thanks.
but cout<<v[2] is not.

[Moha]

at function is slow! because it checkes the index! use iterators or [] instead

[Martin Macko]

cout<<(*v)[2]
its working thanks.
but cout<<v[2] is not.

Note the 'reference to' symbol & in mf's code. If you replace the 'poiner to' symbol * by 'reference to' symbol, the expression cout<<v[2] will work.

[Quantris]

I think v->operator[](2) works too (but it's somewhat ugly).

I'm not sure what you mean when you say iterators are slow, because something like *(v->begin() + 2) is still constant-time.

I do prefer the pass-by-reference method here though - don't use a pointer unless there is a specific reason to (especially if you don't understand how pointers work )