Re: need help on coding grammar about reference / pointer /instance.

=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <>
Sat, 27 May 2006 10:10:32 GMT
On 2006-05-27 10:06, key9 wrote:

Hi All

On coding , I think I need some basic help about how to write member
function .

I've readed the FAQ, but I am still confuse about it when coding(reference /
pointer /instance) , so I think I need some "template".
Sorry for my coding experience in c++

You should be careful when talking about templates in here since there
is something called templates in C++, but it's not what you want.

Suppose we have

class FooClass{


  foo() // this is what I want to ask below

    string str;

What I need "template" is:

1. Use a outside string (string*,string&) to replace string content in class
string* outp;
string outi;
string& outr;
how to write these three foo()?

If I understand you correctly what you are asking for is something lika

// Using a pointer
FooClass::foo(string* s)
     srt = *s;

// Using a reference
FooClass::foo(string& s)
     str = s;

// Using a copy
FooClass::foo(string s)
     str = s;

Whenever possible it is preferable to use a reference instead of a
pointer, and often instead of using a copy too.

2. 1 outside will get string content inside of class, but outside can not
change it, (return a copy/return const pointer)
2. 2 outside will get string content inside of class, but outside can change
it, (return a point/reference)

3. outside can get string which have processed in foo()
   string* foo(){
     string* temp;
     temp = processof(str);
     return temp*
  how to use autoptr to void mem leak? if I forgot delete temp* outside?

Supposing str already has some value it can be returned like this:

// Using a pointer
string* FooClass::foo2()
     return &str;

// Using a reference
string& FooClass::foo2()
     return str;

// Using a copy
string FooClass::foo2()
     return str;

When returning a pointer or reference the user can later change the vlue
of str without calling foo() since it can manipulate the pointer/
reference directly, thus it's often a good idea to return a copy (unless
you want this behaviour).

Notice also that you should never return a pointer or reference to a
object declared inside the function returning it since the object will
no exist after the function has returned but the pointer/reference will
still point to it.

Erik WikstrFm
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