value_type of vector

**George2** · 11-18-2007

Hello everyone,

I think the value_type of vector<int> should be int and the value_type of vector<int> should be int*. But I am not 100% sure,

1. how to write a program to verify this idea;
2. where to find the definition that the value_type of interator of vector<int> is int*.

It is appreciated if you could help.

Code:

#include <vector>

using namespace std;

int main (int argc, char** argv)
{
	vector<int>::value_type;  // should be int ?
	vector<int>::iterator::value_type; // should be int* ?

	return 0;
}

thanks in advance,
George

**laserlight** · 11-18-2007

I think the value_type of vector<int> should be int and the value_type of vector<int> should be int*

That sounds like a contradiction

The value_type of vector<int> is int. But vector<int>::iterator may not necessarily be a pointer type, so we cannot say for sure if it is actually an int*.

**cpjust** · 11-18-2007

The implementation of iterators is undefined in the C++ standard and can vary from compiler to compiler. It may be a pointer on one system, but it could be some type of object on another system.

**anon** · 11-19-2007

Well, it is a type. You think it is a int*, so declare an iterator::value_type variable and try to assign a pointer to it.

Code:

#include <vector>

int main()
{
    int* p = 0;
    std::vector<int>::iterator::value_type c = p;
}

Nope, I get

Untitled1.cpp:6: error: invalid conversion from `int*' to `int'

Make your conclusions.

You might also try and locate this typedef in your STL implementation.

**CornedBee** · 11-19-2007

For any standard container C, it is guaranteed that C::value_type == std::iterator_traits<C::iterator>::value_type. Everything else would be stupid. The iterator over a container refers to the elements of the container, thus the referred-to type of the iterator (its value_type) must be the same as the element type of the container (its value_type).

**laserlight** · 11-19-2007

George2 pretty much had his question answered in another community that some of us here visit: value_type of vector

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