vectors and arrays

[Dave Rahardja]

Is there a way to easily convert between a std::vector and a C-style array?

In the Microsoft C++/Dinkumware library, std::vector::begin() returns a
pointer to the data type and not some custom iterator for all types except
bool. This pointer can then be used as the base pointer to the array.

I don't think this is standard behavior, and I believe the cast is strictly
incorrect according to the STL standard. Am I right, or can I expect certain
types such as std::vector<int> to be cast-able to an array?

-dr

 

[red floyd]

Is there a way to easily convert between a std::vector and a C-style array?

In the Microsoft C++/Dinkumware library, std::vector::begin() returns a
pointer to the data type and not some custom iterator for all types except
bool. This pointer can then be used as the base pointer to the array.

I don't think this is standard behavior, and I believe the cast is strictly
incorrect according to the STL standard. Am I right, or can I expect certain
types such as std::vector<int> to be cast-able to an array?

-dr

assuming you have a prototype:

void f(T*, int nElems);

and a vector:

vector<T> v;

Then you can call:

f(&v[0],v.size());

 

[Ivan Vecerina]

Is there a way to easily convert between a std::vector and a C-style
array?

The elements of a vector are required to be stored contiguously,
and may therefore be accessed as an array.
For a **non-empty** vector v, a pointer to the first element can
be obtained with &v.front() , or &v[0] . or &*v.begin() .
NB: if v is empty, each of the above expressions will trigger
undefined behavior, so make sure to check for this case.

In the Microsoft C++/Dinkumware library, std::vector::begin() returns a
pointer to the data type and not some custom iterator for all types except
bool. This pointer can then be used as the base pointer to the array.

This is an allowed behavior, but you cannot rely on it portably.

I don't think this is standard behavior, and I believe the cast is
strictly
incorrect according to the STL standard. Am I right, or can I expect
certain
types such as std::vector<int> to be cast-able to an array?

Equivalence of iterator and pointer is not portable.
Contiguous storage (and accessibility as a C array) is guaranteed.

hth-Ivan

 

[Dave Rahardja]

Equivalence of iterator and pointer is not portable.
Contiguous storage (and accessibility as a C array) is guaranteed.

I did not know that about contiguous storage. Thank you.

-dr