Fwd: RE: [Dev-C++] [Dev-C++]: Errors in structures

[Johannes P. <joh...@pr...>]

>Date: Tue, 03 Jul 2001 09:16:19 +0200
>To: dev...@li...
>From: Johannes Pretorius <joh...@pr...>
>Subject: RE: [Dev-C++] [Dev-C++]: Errors in structures
>
>
>Action : Response
>Mood : Friendly
>Subject : Data Type mismatch in C/C++ gcc ,mingW32 compiler
>
>Considering this Feature . It is making it hard to read a fixed structure 
>size from a file or a memory stream for
>instance for the compiler has decided that the structure must be 
>optimized. Meaning that if a other compiler
>created the file then the program will not read the correct size of the 
>contents in to contain all the data.
>
>Considering this if I turn all compiler option of from the DevC++ IDE the 
>result is still the same.
>else I dont know or cant see how this can be usefull in complaince wise..
>
>Or am I missing something ???
>
>Thanks for your help so far
>
>Johannes
>
>
>
>At 11:35 04/07/2001 +0530, you wrote:
>>It is not a bug, it is compiler feature. For some optimizations some c++
>>compilers adjust the size of structue to the multiple of 8.
>>
>>
>>Hi there
>>-------------
>>I am sorry to say that I dont have an answer for you . The LibC help file
>>does say that the Data Types can vary from Compiler
>>to Compiler But I WOULD like to show what I have also picked up with your
>>Code
>>
>>//Snippet - START
>>#include <iostream.h>
>>#include <stdlib.h>
>>#include <limits.h>
>>
>>struct tea_hdr{
>>   int version; //-- 1
>>   char jte[3]; //  -- 2
>>   //char fname_sz; // -- 3
>>   //char infile_size; // -- 4
>>// char infile_crc; // -- 5
>>
>>   }header;
>>
>>
>>int main()
>>{
>>        cout<<"Char Minimum : "<<CHAR_MIN<<endl;
>>        cout<<"Char Max : "<<CHAR_MAX<<endl;
>>        cout<<"Unsigned Char Max : "<<UCHAR_MAX<<endl;
>>        cout <<"Header : "<<sizeof(header)<<endl;
>>        cout<<"Struct : "<<sizeof(tea_hdr)<<endl;
>>        system("PAUSE");
>>        return 0;
>>}
>>
>>//Snippet END
>>
>>Now if you compile it as follow the Size of the Structure is 8 (The integer
>>(5) and the char[3]) That is ok.,
>>
>>Now remove the comment before item 3 and compile and run Again.. The size
>>is STILL the same ?? Is this just my
>>PC.. must I reboot.. BUT there is more.
>>
>>Now uncomment item 4 .. Compile and RUN.. SIZE is 12 that is 4 bytes
>>extra,But there is still more
>>
>>Now uncomment item 5 and compile and run.. IT stays at 12 bytes again..
>>This seems to be variable
>>items count related. I have sifted the vars around and nothing is with
>>there posisions..
>>Also it only starts when MIXING variables in the structure.. I have a
>>feeling that this is something
>>that can be compiler related.. BUT what I did notice in the 'stddef.h' File
>>is that the MingW32 oaks have
>>a prob with the defs of the Gcc compiler and has added some macro to fix it
>>.. I wonder if maybe something else
>>also was missed that can relate to this. That the problem can maybe be at
>>the MingW32 project.
>>
>>I don't have any answer's just maybes. but maybe it can help you in getting
>>to a answer For IF I cam correct you are trying to
>>read the information into the structure from a File .. like the header of a
>>MP3..
>>
>>I dont have any other Ideas atound this but I hope you get a solution
>>
>>Good luck
>>
>>Johannes
>>
>>
>>
>>
>>
>>
>>At 09:22 03/07/2001 +0530, you wrote:
>> >Hi,
>> >
>> >I've noticed this strange little Bug.I'm not certain weather its a bug or a
>> >feature.
>> >
>> >The size of this structure is actually 13 bytes.
>> >
>> >But sizeof(header) says its 16.
>> >
>> >struct tea_hdr
>> >  {
>> >  char jte[3];
>> >  unsigned char version;
>> >  DWORD infile_size;
>> >  DWORD infile_crc;
>> >  unsigned char fname_sz;
>> >  }header;
>> >
>> >No, if I comment out the fname_sz member,
>> >
>> >struct tea_hdr
>> >  {
>> >  char jte[3];
>> >  unsigned char version;
>> >  DWORD infile_size;
>> >  DWORD infile_crc;
>> >  //unsigned char fname_sz;
>> >  }header;
>> >
>> >sizeof(header) returns 12.
>> >
>> >Is the compiler trying to align structure on DWORD boundaries?
>> >
>> >How do I get rid of this Bug/Feature ?
>> >
>> >Thnx,
>> >Jeethu Rao
>> >
>> >
>> >_______________________________________________
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>>
>>
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