Re: sizeof array via pointer

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Wed, 08 Apr 2009 08:48:37 +0200

Message-ID:

<grhhfv$olu$1@news.motzarella.org>

* Mark S.:

Hi,
I want to access an array via a pointer and get the size of the array,
but sadly I don't know the correct syntax for it:

int main()
{
    char c[10];
    char* cp = c;
    cp[3] = 'b'; // works
    int a = sizeof(cp); // this doesn't (returns 4 - why???)

It giveth the size of the pointer.

a = sizeof(*cp); // neither does this (returns 1)

It giveth the size of the pointer's referent, a 'char'.

}

So how do I get the correct size of c via the pointer (of course, the
goal is to use this within a function)???

You can't get the array size via the pointer.

The information simply isn't there, at least as far as standard C++ is concerned.

Instead of raw arrays, use a std::vector or a std::string.

   #include <vector>
   #include <iostream>

   int main()
   {
       using namespace std;
       vector<char> c( 10 );

       c.at( 3 ) = 'b';
       cout << v.size() << endl;
   }

Cheers & hth.,

- Alf

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