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Date: Mon, 26 Dec 2011 11:57:00 -0000
Message-ID: <CAH6eHdQ6iQwMTQJ_oUSg67M9CTOhuO1nPZL6Y990oGNE6C166A@mail.gmail.com>
Subject: Re: string in structure and fread()
From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: =?ISO-8859-1?Q?Juan_Ram=EDrez?= <jramirez@inconcertcc.com>
Cc: Mohsen Pahlevanzadeh <mohsen@pahlevanzadeh.org>, gcc-help <gcc-help@gcc.gnu.org>
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2011/12/25 Juan Ram=EDrez:
> Hi,
>
> If you want to write and read a raw structure to a file, using c++
> objects is NOT recommended at all! At least not using fread/fwrite

What do you mean by "c++ objects"?

A POD struct is a "c++ object"

Assuming you mean non-POD class types with non-trivial constructors
and/or non-POD members, I strongly disagree, there is nothing wrong
with doing IO with suh types, you just need to write the IO code
correctly, which is always true.


> Given that fields have fixed length, a good solution could be using a
> raw char array, something like this:
>
> =A0 =A0 #define FIELD_LENGTH =A0 101
>
> =A0 =A0 struct book {
> =A0 =A0=A0=A0 =A0=A0char name[FIELD_LENGTH];
> =A0 =A0=A0=A0 =A0=A0char author[FIELD_LENGTH];
> =A0 =A0=A0=A0 =A0=A0char publisher[FIELD_LENGTH];
> =A0 =A0=A0=A0 =A0=A0char translator[FIELD_LENGTH];
> =A0 =A0=A0=A0 =A0=A0bool translation;
> =A0 =A0=A0=A0 =A0=A0bool stock;
> =A0 =A0=A0};

That solution is useless if the strings can be arbitrarily long, a
better solution is to store the strings in the file as
null-terminated, or length-prefixed, and in either of those cases
managing the strings in the program will be simpler with std::string.