Re: Creating an instance of a class
jimbo wrote:
Dear all,
I am more or less new to c++ programing and therefore still have
problems with some fundamentals :(
At the moment I try to build a GUI-Application with Qt4. Sometimes I
have seen in the tutorials I have to instance a class with the new
command. Like QWidget QLabel *label = new QLabel("Hello World"); Then
I have created a pointer to a QLabel Object. The other way I have seen
is to just use QLabel label("Hello World"); Without a pointer and
without the new statement.
So to access the functions of the QLabel class I have to use the "."
for the part without pointer like label.show and for the pointer part:
label->show.
Can somebody explain me, why it is possible to use the two ways and
what is the difference in general.
Thank you a lot in advance.
jimbo
Given an object and a pointer to that object, you can access members
like so:
class foo
{
public:
int bar;
};
int
main()
{
foo* baz1 = new foo();
foo baz2;
baz2.bar; // cool
baz2->bar; // not cool
baz1.bar; // not cool
(*baz1).bar; // cool but too long
(baz1)->bar; // short hand version of the previous line
baz1->bar; // even shorter version of the previous line
}
In summary, "->" is a short hand notation to dereference the
pointer first and then access its member.
Good Luck!
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