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From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c++
Subject: Re: value of 'this' in constructor
Message-ID: <2655@dataio.Data-IO.COM>
Date: 17 Aug 90 18:18:30 GMT
References: <12680@hydra.gatech.EDU>
Distribution: na
Organization: Data I/O Corporation; Redmond, WA
Lines: 36

In article <12680@hydra.gatech.EDU> gt3930b@prism.gatech.EDU (NICHOLS,STEVEN MALCOLM) writes:
<	Consider the following piece of code.  From p. 284 of "Using
<C++", and also p. 164 of "The C++ Programming Language", I am lead to 
<believe that the value of the pointer 'this', on entry to a constructor,
<will be 0 if the instance of the class has been dynamically allocated.
<If the class has been statically allocated, the value of 'this' will be
<non-zero.  However, I see non-zero values for this for both static and dynamic
<instances of the class test in the code fragment that follows. 
<#include <stream.hpp<
<class test
<{
<   test* this_on_entry;
<public:
<   test() { this_on_entry = this; }

This will not give the value of 'this' upon entry, because the compiler
inserts a call to new() before any user statements in the constructor.

<   void show() {cout << "this_on_entry = " << (unsigned)this_on_entry << "\n"; }
<};
<
<main()
<{
<   test static_test;
<   test* dynam_test;
<
<      dynam_test = new test;
<      cout << "static:";
<      static_test.show();
<      cout << "dynamic:";
<      dynam_test-<show();
<}
<
<// the output from ZORTECH
<static:this_on_entry = 9128
<dynamic:this_on_entry = 9170