Bug#259318: marked as done (pass by reference broken)
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and subject line Bug#259318: pass by reference broken
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>From abgrover@cc.usu.edu Tue Jul 13 17:06:30 2004
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From: Alan <abgrover@cc.usu.edu>
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Subject: pass by reference broken
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Package: g++-3.3
Version: 1:3.3.4-2
Pass by reference seems to be broken in g++.
Originally I thought the problem might be in ntohl, which is why it
appears in the test below. However, the real problem seems to be in the
mechanics of passing data. A different variant of the program below
showed no problems in ntohl. I also considered casting as the source of
the problem, but that also seems to work fine.
The program below gave the following output when compiled with g++-3.3
3.3.4 (Debian 1:3.3.4-2) :
alan@1[alan]$ ./testp
cast test: tmp is 4294967295, result is -1
ntohl test: result is -1
And the following correct output when compiled with g++-3.2 3.2.3 (Debian):
alan@1[alan]$ ./testp
cast test: tmp is 4294967295, result is -1
ntohl test: result is -6
This seems to show that result might have been passed by value instead
of by reference, since the value of result does not change.
Here is the test program:
// ------------begin test program---------------
#include <stdio.h>
#include <netinet/in.h>
#include <stdint.h>
uint32_t Read (uint32_t& v, char * buf);
int32_t Read (int32_t& v, char * buf);
int
main()
{
char buffer[] = {
255, 255, 255, 250 // -6 in network byte order
};
int32_t result = -1;
uint32_t tmp = static_cast<uint32_t>(result);
result = static_cast<int32_t>(tmp);
printf("cast test: tmp is %u, result is %d\n", tmp, result);
Read(result, buffer);
printf("ntohl test: result is %d\n", result);
return 0;
}
int32_t
Read(int32_t& v, char * buf)
{
Read(static_cast<uint32_t>(v), buf);
return v;
}
uint32_t
Read(uint32_t& v, char * buf)
{
v = ntohl(*(reinterpret_cast<uint32_t*>(buf)));
return v;
}
//------------end test program------------------------------
---------------------------------------
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for <259318-done@bugs.debian.org>; Wed, 14 Jul 2004 08:44:17 +0200
To: 259318-done@bugs.debian.org
Subject: Re: Bug#259318: pass by reference broken
References: <[🔎] 40F47CB0@webster.usu.edu>
From: Falk Hueffner <hueffner@informatik.uni-tuebingen.de>
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Date: Wed, 14 Jul 2004 08:44:17 +0200
In-Reply-To: <[🔎] 40F47CB0@webster.usu.edu> (Alan's message of "Tue, 13 Jul 2004
18:05:58 -0600")
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Alan <abgrover@cc.usu.edu> writes:
> uint32_t Read (uint32_t& v, char * buf);
>
>
> Read(static_cast<uint32_t>(v), buf);
Initialization of a non-const reference from a temporary is invalid.
Newer g++ will even diagnose this and error out.
--
Falk
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