Can I call functions that take an array/pointer argument using a std::vector instead?

Question

I want to rewrite some code that uses a lot of unsigned char arrays, to instead make use of std::vector<unsigned char> objects. The problem I have is that these are currently used to store the data that will be written to either a serial port or socket write buffer and the library functions to do this take either void* or unsigned char* . An example of such a function is

  WriteToSocketBuffer(unsigned char* pBuffer, int iSize);

so currently I have code of the form

 unsigned char* pArray = new unsigned char[iSize];
 //   populate array with data
 WriteToSocketBuffer(pArray,iSize);
 delete [] pArray;

My question is the following: If I change my class to have a std::vector<unsigned char> instead of a raw array can I simply call my library function using

  std::vector<unsigned char> myVector;
  WriteToSocketBuffer(&myVector[0],myVector.size());

Does passing the address of the first element in the vector act in the same was as passing in the address of the first element in a raw array. Is it this simple?

@DragoonWraith, how trying would help? Things like allowing non contiguous representation may break it in general and yet succeed in basic tests. — AProgrammer
– AProgrammer, Commented Aug 21, 2012 at 16:05
@DragoonWraith Rather than rewrite core functionality that will take a week and massively impact on my code internals, I thought I would ask the question first just to check that what I suspect will happen actually will happen. — mathematician1975
– mathematician1975, Commented Aug 21, 2012 at 16:08
Note that as-written this is undefined behavior, because myVector contains no elements. You want std::vector<unsigned char> myVector(iSize); instead. — GManNickG
– GManNickG, Commented Aug 21, 2012 at 18:41
@GManNickG Yes indeed, I omitted the populating of the vector. I was really just trying to convey the general idea. I should have inserted a commented code line for clarity. — mathematician1975
– mathematician1975, Commented Aug 21, 2012 at 19:24

David Rodríguez - dribeas · Accepted Answer · 2012-08-21 16:19:33Z

12

Yes, The elements of a vector are assured to be contiguous similar to an array.

Reference:

C++03 Standard: [lib.vector] 23.2.4 Class template vector

......
The elements of a vector are stored contiguously, meaning that if v is a vector<T, Allocator> where T is some type other than bool, then it obeys the identity &v[n] == &v[0] + n for all 0 <= n < v.size()

edited Aug 21, 2012 at 16:19

David Rodríguez - dribeas

209k23 gold badges304 silver badges497 bronze badges

answered Aug 21, 2012 at 16:04

Alok Save

208k56 gold badges449 silver badges540 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

mathematician1975 Over a year ago

I thought it would probably be OK but thanks for confirming it.

Jerry Coffin · Accepted Answer · 2012-08-21 16:07:17Z

6

C++98 didn't mandate contiguous allocation for the data in an std::vector, but that's what all known implementations did anyway.

As of C++03, that was standardized as a requirement, so it's now required, not just how things happen to be.

answered Aug 21, 2012 at 16:07

Jerry Coffin

494k83 gold badges657 silver badges1.2k bronze badges

Comments

Adrian McCarthy · Accepted Answer · 2012-08-21 16:31:47Z

2

Yes, you can do that, as long as the buffer is never empty.

If the vector is ever empty, then &buffer[0] is an error, and it will likely crash even though the called function wouldn't normally dereference the pointer because the size is 0.

answered Aug 21, 2012 at 16:31

Adrian McCarthy

49.9k16 gold badges136 silver badges194 bronze badges

Collectives™ on Stack Overflow

Can I call functions that take an array/pointer argument using a std::vector instead?

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related