CODEWITHSUNDEEP
c++
usustarr
usustarr

Reputation: 11

how to creater pointer to update a dynamic STL vector in C++?

I have a dynamic array which will be updated from a different test system. I am havign hard time with syntax. Can someone please help me here?

Here is where I declare my vector

  void TestSystem::Drive(U32 RunMode, U32 Options)

  { //U32 is unsigned 32 bit



  U32 condition;

  U32 i;

  U8 k;

  vector<U32> badDriveList(1,0);//initial size of vector is 1 and value is 0

  int *badDrivePointer[&badDriveList];



  bool driveStatus = testSystems[k]->DriveCheck(badDrivePointer);//should this be &badDrivePointer?

  // left side to "->" is correct. After that i am not sure

  }

Here is where I update my vector. 

  int TestSystem::DriveCheck(int *badDriveList)

  {

  U32 condition;

  U32 i= 10;

  U32 j = 0;



  for(j;j<i;j++)

  {

  badDriveList[j] = (*i)->shelf;//right hand side of this is working when tested with complete code base

  //I am not sure how to write values in to badDriveList vector using pointers

  }

  }

here is part of my .h file

 int DriveCheck(int *);

Upvotes: 1

Views: 232

Answers (2)

Saxon Druce
Saxon Druce

Reputation: 17624

You can do this to get a pointer to the data in your vector:

U32 *badDrivePointer = &badDriveList[0];

However, your vector only has a single element in it. Therefore in TestSystem::DriveCheck(U32 *badDriveList) you can only write a single element, eg:

badDriveList[0] = something;

If you need to be able to write 10 elements into the vector from within TestSystem::DriveCheck(), then you need to allocate those 10 elements first. You need to do that before you use &badDriveList[0] to get a pointer to the data in the vector, because resizing a vector can reallocate the data, making a pointer retrieved earlier invalid.

If you don't know how many elements you need to put into the vector, then you would be better off passing a reference to the vector to TestSystem::DriveCheck(), so that you can update the vector directly (instead of via a pointer). For example:

int TestSystem::DriveCheck(vector<U32>& badDriveList) 
{ 
    badDriveList.push_back(something);
}

Upvotes: 1

Alex Martelli
Alex Martelli

Reputation: 881705

You cannot properly use a pointer to update a STL container -- rather, you need to use an iterator. The insert_iterator adapter in particular seems to be what you're looking for.

Upvotes: 2

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