C++ Programming :: class instantiation


	class instantiation Hi, Assume we have a class called A. Assume it has a constructor which takes an integer as its input. What is the difference between these two instantiations? A a(1); and A a=new A(1); Thanks. Sara sara wrote: > Assume we have a class called A. Assume it has a constructor which > takes an integer as its input. What is the difference between these > two instantiations? > A a(1); > and > A a=new A(1); The difference is the first is allowed, and the second will give you syntax error, because your object should be a pointer to initialize it like that. On 4 Juni, 11:51, sara <sarasar@gmail.com> wrote: > Hi, > Assume we have a class called A. Assume it has a constructor which > takes an integer as its input. What is the difference between these > two instantiations? > A a(1); > and > A a=new A(1); Consider the following code: void test() { A foo(1); A* bar = new A(1); } In this case both will create a new instance of an object of type A, but foo will be destroyed as soon as test() returns, because it's lifetime is limited by the scope in which it was created. bar on the other hand will continue to exist until you use 'delete' to destroy it, its lifetime is not limited. In general you should use the first type when you can and the second when you must. -- Erik Wikstrm In the first step, you are creating a local object whereas in the second step (assuming you have missded A) you are creating object pointer. The local object will be destroyed as soon as you get out of function where A a(1) is defined whereas the pointer will linger until you call delete A. Hope this makes it clear. Vaibhav <vaibhav.pa@gmail.com> wrote in message... > In the first step, you are creating a local object whereas in the > second step (assuming you have missded A) you are creating object > pointer. > The local object will be destroyed as soon as you get out of function > where A a(1) is defined whereas the pointer will linger until you call > delete A. > Hope this makes it clear. Makes WHAT clear? Please read this before your next post: http://www.parashift.com/c++-faq-lite/how-to-post.html