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From: poffen@sj.ate.slb.com (Russ Poffenberger)
Newsgroups: comp.lang.c++
Subject: Re: How to correctly initialize struct/class
Message-ID: <1990Aug21.225257.13186@sj.ate.slb.com>
Date: 21 Aug 90 22:52:57 GMT
References: <1990Aug20.220157.24736@sj.ate.slb.com> <406@taumet.com>
Reply-To: poffen@sj.ate.slb.com (Russ Poffenberger)
Organization: Schlumberger Technologies, San Jose, CA.
Lines: 98

In article <406@taumet.com> steve@taumet.com (Stephen Clamage) writes:
>poffen@sj.ate.slb.com (Russ Poffenberger) writes:
>
>|I want to define a union, such that it can be either a float value, or a
>|pointer.
>|
>|union both {
>|  float value;
>|  float *value;
>|};
>|
>|Now I want to define a structure (or class) like so that uses several instances
>|of this union.
>|
>|struct data {
>|  union both one;
>|  union both two;
>|  union both three;
>|  union both four;
>|  union both five;
>|};
>|
>|Now what I need to do is to declare an instance of the struct, but initialize
>|all of the fields. Any of the fields may be initialized to either a floating
>|point constant, or the address of a floating variable.
>|
>|e.g.
>|
>|float f1;
>|float f2;
>|
>|struct data d1 = (&f1,4.3,&f2,7.2,0.0)
>|struct data d2 = (0.0,1.0,2.0,3.0,4.0)
>|
>|etc...
>|
>|How can I declare a constructor to do this? Is it even possible?
>
>Try this:
>
>class ugly {
>    union {
>	float f;
>	float* p;
>    };
>public:
>    ugly(float  x) { f = x; }
>    ugly(float* x) { p = x; }
>};
>
>class data {
>    ugly u1;
>    ugly u2;
>    ugly u3;
>    ugly u4;
>    ugly u5;
>public:
>    data(ugly a1, ugly a2, ugly a3, ugly a4, ugly a5) {
>	u1 = a1;
>	u2 = a2;
>	u3 = a3;
>	u4 = a4;
>	u5 = a5;
>    }
>};
>
>Now you can use
>	float f1;
>	float f2;
>
>	data d1(&f1, 4.3, &f2, 7.2, 0.0);
>	data d2(0.0, 1.0, 2.0, 3.0, 4.0);
>-- 
>
>Steve Clamage, TauMetric Corp, steve@taumet.com


When I try this with g++ (version 1.37.1) I get the following errors..

test_union4.cc: In method data::data (class ugly, class ugly, class ugly, classugly, class ugly):
test_union4.cc:26: too few arguments for constructor `ugly'
test_union4.cc:26: in base initialization for class `ugly'
test_union4.cc:26: too few arguments for constructor `ugly'
test_union4.cc:26: in base initialization for class `ugly'
test_union4.cc:26: too few arguments for constructor `ugly'
test_union4.cc:26: in base initialization for class `ugly'
test_union4.cc:26: too few arguments for constructor `ugly'
test_union4.cc:26: in base initialization for class `ugly'
test_union4.cc:26: too few arguments for constructor `ugly'
test_union4.cc:26: in base initialization for class `ugly'

I will try it tonight on TC++ 1.0 and see what happens.


Russ Poffenberger               DOMAIN: poffen@sj.ate.slb.com
Schlumberger Technologies       UUCP:   {uunet,decwrl,amdahl}!sjsca4!poffen
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