pointer didnt locate the right place~

Please check the code below first, the pointer didnt point to the a.

PHP Code:

#include <iostream>

void main()
{
  int a=0;
  typedef int * pt_int;
  pt_int pa;
  *pa=a;
  cout << &a << endl;
  cout << pa << endl;
} 


anyone could figure out why *pa=a failed ?

>*pa=a;
This should be

pa = &a;

You are assigning a value to a pointer, which is not an address. pa at this point hasn't been initialized so it points to some random address. Thus dereferencing is a bad idea.

>void main()
This should be

int main()

main returns an int, anything else is undefined, which is very bad.

-Prelude

that is to say, only when an address is passed to the pointer it could be initialized, yes ?

>main returns an int, anything else is undefined, which is very bad.

I tested void and it just works fine. What's the matter please ?



thanx in advance~

>that is to say, only when an address is passed to the pointer it could be initialized, yes ?
A pointer variable must contain a valid address before you can dereference it safely. It's just like any other variable, it has to contain something valid to be of use. The only difference is that a pointer variable holds an address as its value.

>I tested void and it just works fine. What's the matter please ?
It may work for you and it may work for me, but undefined means that anything can happen, re-formatting your hard drive without your consent for example. Undefined is about as bad as it gets and you should avoid anything that results in such behavior.

-Prelude

many compilers safeguard void main. many dont. it's not like it takes any extra work to write int main() then return something

>it's not like it takes any extra work to write int main() then return something
You don't even have to do that. If main is defined as returning int then 0 is returned by default without any need to explicitly do so. This is acceptable and standard C++:

Code:

#include <iostream>

int main()
{
  std::cout<<"Hello, world!\n";
}

-Prelude

>>int main()
>>main returns an int, anything else is undefined, which is very bad.

Is this the fact that void main do return a value of somewhat undefined type ?

I considered it never returns anything.

black~

Is there a standard return value from main to indicate successful program termination? Should I be returning a non-zero digit for success?

> I tested void and it just works fine
Yeah, and writing to an uninitialised pointer can work fine as well - for a while. The fact that your current compiler does not say there is a problem does not mean that the program is in any way bug free, nor is a program which contains bugs obliged to crash at the first instance a rule is broken.

Then all of a sudden, your bad habits catch up with you and bite you in the @ss, say when you upgrade your compiler, move to another compiler, or add that critical line of code which takes it over the edge.

http://www.eskimo.com/~scs/C-faq/q11.12.html

>Is there a standard return value from main to indicate successful program termination?
Yes, there are two. The first is 0, the second is a portable macro defined in <cstdlib>:

return 0;

or

#include <cstdlib>
.
.
return EXIT_SUCCESS;

or you can simply omit the return statement and the value for successful completion ( the equivalent of return 0; ) will be sent automatically...if main was defined as returning int.

-Prelude