String class should be
preferred over dynamically allocated array due to following limitations of dynamically allocated arrays:
- Whenever user calls new operator, it becomes her/his responsibility to delete it as well to avoid memory
leaks.
- User must ensure that
correct form of delete is called. For a single element allocation delete
should be used and for an array allocation delete[] should be used.
If wrong version is used it may result into undefined behavior.
- User has to make sure that there
is single delete for one allocation.
string class provides
function c_str() for backward compatibility with C API's that expects char* as
argument. Hence there is no reason for not to use string in place of array of
char.
But, in Multi-threaded
environment, there can be performance issues with string class
because of reference counting(wiki link) optimization. Basically, reference counting
optimization can eliminate unnecessary memory allocations and copying of
characters. But in multi-threaded environment, time saved by avoiding
unnecessary allocations and copying is dwarfed by time spent on behind the
scenes for concurrency control.
Hence in multi threaded
environment, user has following options :
- Check for library implementation
of string class if it allows you to disable reference counting
optimization.
- check for alternative
implementation of string class that do not have reference-counting
optimization that can be checked in copy constructor of class.
- consider using vector<char>
instead of string. String class' member functions will not be
available but most of the functionality is available through STL
algorithms.
Option 1 & 2 are not
even solutions that are just checking string class or library implementation.
Option 3 is a real solution.
Hope you’ve found this
post useful. Let us know what you think in the comments.
References : Effective STL by Scott Meyer