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Tip of the Day
Language: C++
Expertise: Intermediate
Sep 5, 2000

Container of Pointers

Many programmers believe that by storing pointers instead of objects in a container, they improve performance. However, they forget that the pointers still refer to existing objects that must be stored somewhere. Worse yet, these objects are often allocated dynamically. Dynamic allocation is an expensive operation. Remember also that you have to destroy these objects as well, which is another costly operation. Perhaps the most compelling argument against the use of pointers as container elements is that you can easily avoid the overhead associated with moving objects in memory by pre-allocating enough storage for the container in advance. This will ensure that no reallocation takes place, hence, no objects are moved around. You can pre-allocate storage by calling the reserve() member function:

 
std::vector < std::string > v;
v.reserve(1000);  // make room for at least 1000 strings

In most cases, an empirical test will show that the overall performance of object containers is superior to the performance of pointer containers. In other words, the use of pointers is a classic example of premature optimization.

Danny Kalev
 
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