Vector does reallocation on every push_back

Posted by Amrish on Stack Overflow See other posts from Stack Overflow or by Amrish
Published on 2010-04-27T19:47:31Z Indexed on 2010/04/27 19:53 UTC
Read the original article Hit count: 222

Filed under:

vector

|

push-back

IDE - Visual Studio 2008, Visual C++

I have a custom class Class1 with a copy constructor to it.
I also have a vector
Data is inserted using the following code

 Class1* objClass1;
 vector<Class1> vClass1;

 for(int i=0;i<1000;i++) {
objClass1 = new Class1(); vClass1.push_back(*objClass1); delete objClass1; }

Now on every insert, the vector gets re-allocated and all the existing contents are copied to new locations. For example, if the vector has 5 elements and if I insert the 6th one, the previous 5 elements along with the new one gets copied to a new location (I figured it out by adding log statements in the copy constructors.)

On using reserve(), this however does not happen as expected! I have the following questions

Is it mandatory to always use the reserve statement?
Does vector does a reallocation every time I do a push_back; or does it happen because I am debugging?

© Stack Overflow or respective owner

Related posts about vector

vector iterator not dereferencable at runtime on a vector<vector<vector<A*>*>*>

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I have this destructor that create error at runtime "vector iterator not dereferencable". The gridMatrix is a std::vector<std::vector<std::vector<AtomsCell< Atom<T> * > * > * > * > I added the typename and also the typedef but I still have the error. I will move… >>> More
Adding Functions to an Implementation of Vector

as seen on Stack Overflow - Search for 'Stack Overflow'
I have this implementation of vector that I've been working on for a few days using examples from a textbook: #include <iostream> #include <string> #include <cassert> #include <algorithm> #include <cstring> // Vector.h using namespace std; template <class T> class… >>> More
Making only the outer vector in vector<vector<int>> fixed

as seen on Stack Overflow - Search for 'Stack Overflow'
I want to create a vector<vector<int>> where the outer vector is fixed (always containing the same vectors), but the inner vectors can be changed. For example: int n = 2; //decided at runtime assert(n>0); vector<vector<int>> outer(n); //outer vector contains n empty vectors outer… >>> More
(R) How can I get the complement of vector y in vector x

as seen on Stack Overflow - Search for 'Stack Overflow'
That's x \ y using mathematical notation. Suppose x <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,2,1,1,1,3) y <- c(0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1) How can I get a vector with ALL the values in x that are not in y. i.e the result should be: 2,1,1,3 There is a similar question here… >>> More
C++: Appending a vector to a vector

as seen on Stack Overflow - Search for 'Stack Overflow'
Assuming I have 2 STL vectors: vector<int> a; vector<int> b; Let's also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b and adding each element via push_back, though I wouldn't like to do that! >>> More

Related posts about push-back

Push back rectangle where collision happens

as seen on Game Development - Search for 'Game Development'
I have a tile collision on a game I am creating but the problem is once a collision happens for example a collision happens in right side my sprite cant move to up and bottom :( thats because i set the speed to 0. I thinks its wrong. here is my code: int startX, startY, endX, endY; float pushx… >>> More
pushing back an boost::ptr_vector<...>::iterator in another boost::ptr_vector?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi all, I have the following code (just typed it in here, might have typos or stuff): typedef boost::ptr_vector<SomeClass> tvec; tvec v; // ... fill v ... tvec vsnap; for(tvec::iterator it = v.begin(); it != v.end(); ++it) { if((*v).anyCondition) vsnap.push_back( it ); // (*it)… >>> More
Vector does reallocation on every push_back

as seen on Stack Overflow - Search for 'Stack Overflow'
IDE - Visual Studio 2008, Visual C++ I have a custom class Class1 with a copy constructor to it. I also have a vector Data is inserted using the following code Class1* objClass1; vector<Class1> vClass1; for(int i=0;i<1000;i++) { objClass1 = new Class1(); vClass1.push_back(*objClass1); … >>> More
push_back private vectors with 2 methods, one isn't working

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a class with a private vector of doubles. To access or modify these values, at first I used methods such as void classA::pushVector(double i) { this->vector.push_back(i); } double classA::getVector(int i) { return vector[i]; } This worked for a while until I found I would have to overload… >>> More
c++ push_back doesn't work as it is supposed

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a class symbol_table that has a vector of objects of another class row_st.also I have an enter method where inserts objects of row_st with a passed name into the vector of desired symbol_table.but when I call the enter to enter objects with name : a;b;c;Iwill get the following result: a,b,c;b… >>> More