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List: kde-devel
Subject: Re: Can anyone give me a push in the right direction?
From: Emily Ezust <gexcfxyy () umail ! corel ! com>
Date: 2000-02-24 17:34:11
[Download RAW message or body]
Hi Peter!
May we see the main program - or the part that creates the object
in question? It's difficult to tell exactly, but I suspect there's
a non-initialized pointer involved somewhere.
Also, I'd like to strongly encourage you not to make data public
(as you did with bits). In object-oriented programming, you want
to restrict access to the data - it makes things easier to maintain
and debug, and if you later decide to change your implementation,
you don't have to change the entire app. Look up "encapsulation"
or "data hiding" in a C++ book if you need some more specific
arguments and examples for this.
Peter Thorstenson wrote:
>
> Hi!
>
> I'm learning C++ and have been using kdevelop since 2 months.
> My application for KDE 1.X is getting along over my expectations. That means
> good.
> However, three days ago I ran in to a problem that does not let me continue.
> Any help is appreciated.
>
> Problem description:
> A added a new class to my project. In this class I declare a variable as
> public.
> This means that any other class should be able to set or alter the value of
> this variable.
> I works fine if I do it from my view-class. There I can alter the value of
> the variable without problems.
> BUT if I try to alter the value from a class that no qt or kde things in it,
> the program quits directly with errors.
> The program compiles fine in both cases. No complaints about missing
> declarations.
> I use the same declaration of the objects: mp3_header header and the same
> way lines to alter the variable.
> In the class I call mp3_headers from:
>
> .h: **************************
> #include >mp3_header.h>
> :
> :
> :
> private:
> mp3_header header;
>
> .cpp: *********************
> header.Load();
>
> The funny thing is that I can't even set the variable from inside it's own
> class...
>
> I must be making a basic misstake. To me it looks so silly, yet I'm not able
> to solve this problem.
> Is there anyone that can give me a push in the right direction.........?
>
> Thanks in advance....
>
> Peter Torstenson
> Rio de Janeiro, 35 degrees Celcius.
>
> code and debug info follows........
> ********* mp3_header.h *****************
> #ifndef MP3_HEADER_H
> #define MP3_HEADER_H
>
> class mp3_header {
>
> public:
> int bits;
> mp3_header();
> ~mp3_header();
>
> // loads the header
> void Load();
>
> };
>
> #endif
> *****************************************
>
> ******** mp3_header.cpp ************
> #include "mp3_header.h"
>
> mp3_header::mp3_header(){
> }
> mp3_header::~mp3_header(){
> }
>
> void mp3_header::Load(){
> /* Here I try to set the variable:bits
> This is where the program exits*/
> bits=1;
> }
> *****************************************
> From de debug:
> (I do not understand much of this..)
>
> MEMORY
> 0x0: Cannot access memory at address 0x0.
>
> DISASSEMBLE
> Dump of assembler code for function readInfo__8mp3_filePCcPc:
> 0x80577c0 <readInfo__8mp3_filePCcPc>: push %ebp
> 0x80577c1 <readInfo__8mp3_filePCcPc+1>: mov %esp,%ebp
> 0x80577c3 <readInfo__8mp3_filePCcPc+3>: sub $0x14,%esp
> 0x80577c6 <readInfo__8mp3_filePCcPc+6>: push %edi
> 0x80577c7 <readInfo__8mp3_filePCcPc+7>: push %esi
> 0x80577c8 <readInfo__8mp3_filePCcPc+8>: push %ebx
> 0x80577c9 <readInfo__8mp3_filePCcPc+9>: push $0xc8
> 0x80577ce <readInfo__8mp3_filePCcPc+14>: call 0x804c6e8 <__builtin_new>
> 0x80577d3 <readInfo__8mp3_filePCcPc+19>: add $0x4,%esp
> 0x80577d6 <readInfo__8mp3_filePCcPc+22>: mov %eax,%eax
> 0x80577d8 <readInfo__8mp3_filePCcPc+24>: mov %eax,0xffffffec(%ebp)
> 0x80577db <readInfo__8mp3_filePCcPc+27>: push $0x1b4
> 0x80577e0 <readInfo__8mp3_filePCcPc+32>: push $0xa1
> 0x80577e5 <readInfo__8mp3_filePCcPc+37>: mov 0xc(%ebp),%eax
> 0x80577e8 <readInfo__8mp3_filePCcPc+40>: push %eax
> 0x80577e9 <readInfo__8mp3_filePCcPc+41>: push $0x1
> 0x80577eb <readInfo__8mp3_filePCcPc+43>: mov 0xffffffec(%ebp),%ebx
> 0x80577ee <readInfo__8mp3_filePCcPc+46>: push %ebx
> 0x80577ef <readInfo__8mp3_filePCcPc+47>: call 0x804c708
> <__8ifstreamiPCcii>
> 0x80577f4 <readInfo__8mp3_filePCcPc+52>: add $0x14,%esp
> 0x80577f7 <readInfo__8mp3_filePCcPc+55>: mov %eax,%edi
> 0x80577f9 <readInfo__8mp3_filePCcPc+57>: jmp 0x8057805
> <readInfo__8mp3_filePCcPc+69>
>
> REGISTERS
> eax 0x8064ef8 134631160
> ecx 0x0 0
> edx 0x0 0
> ebx 0x0 0
> esp 0x7ffff648 0x7ffff648
> ebp 0x7ffff668 0x7ffff668
> esi 0x0 0
> edi 0x80b0818 134940696
> eip 0x8057959 0x8057959
> eflags 0x10206 66054
> cs 0x23 35
> ss 0x2b 43
> ds 0x2b 43
> es 0x2b 43
> fs 0x0 0
> gs 0x0 0
>
> LIBRARIES
> From To Syms Read Shared Object Library
> 0x2aac1000 0x2ab15dcc Yes /usr/lib/libkfile.so.2
> 0x2ab16000 0x2ab25cf0 Yes /usr/lib/libkfm.so.2
> 0x2ab26000 0x2ac2ebe0 Yes /usr/lib/libkdeui.so.2
> 0x2ac2f000 0x2acdcaac Yes /usr/lib/libkdecore.so.2
> 0x2acdd000 0x2aeee1c0 Yes /usr/lib/libqt.so.1
> 0x2aeef000 0x2aefb980 Yes /usr/X11R6/lib/libXext.so.6
> 0x2aefd000 0x2afabf88 Yes /usr/X11R6/lib/libX11.so.6
> 0x2afac000 0x2aff1e30 Yes /usr/lib/libstdc++.so.2.9
> 0x2affa000 0x2b017f08 Yes /lib/libm.so.6
> 0x2b018000 0x2b11269c Yes /lib/libc.so.6
> 0x2aaab000 0x2aabf9b0 Yes /lib/ld-linux.so.2
--
Emily Ezust, emilye@corel.com
Corel Corporation
(613)728-0826, x 5936
--
The address in the headers is not the poster's real email address. Do not send
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The poster's email address is "emilye@corel.com".
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