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From: Ruben Safir <mrbrklyn@panix.com>
Newsgroups: comp.lang.c++
Subject: Re: reading from a temp file
Date: Sat, 2 Jul 2011 00:47:27 +0000 (UTC)
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Michael DOUBEZ <michael.doubez@free.fr> wrote:
> On Jun 28, 10:37=A0am, Ian Collins <ian-n...@hotmail.com> wrote:
>> On 06/28/11 08:34 PM, Ruben Safir wrote:
>>
>> > any clue why this isn't retrieving the contents of the temp file
>>
>> > Question Deck::create_question(WINDOW* menu_win, std::ostream&os ,st=
d::istream&in ){
>>
>> > =A0 =A0 =A0 =A0char default_editor[20000] =3D "vi ";
>> > =A0 =A0 =A0 =A0char * editor;
>> > =A0 =A0 =A0 =A0char tmp[4096];
>> > =A0 =A0 =A0 =A0char path[] =3D "/tmp/fileXXXXXX";
>>
>> Why don't you use strings?
>=20
> because mkstemp expect a char* that is modified. A solution is to
> using std::vector<char> instead.
>=20

std::vector<char> or std::vector<char *> ?


>>
>> > =A0 =A0 =A0 =A0int fd;
>> > =A0 =A0 =A0 =A0fd =3D mkstemp(path);
>> > =A0 =A0 =A0 =A0editor =3D getenv("EDITOR");
>> > =A0 =A0 =A0 =A0if (editor =3D=3D NULL){
>> > =A0 =A0 editor =A0=3D default_editor;
>> > =A0 =A0 =A0 =A0}
>>
>> > =A0 =A0 =A0 =A0strcat(editor, path);
>> > =A0 =A0 =A0 =A0char quest_prompt[] =3D "Edit Your Question";
>> > .....
>> > =A0 =A0 =A0 =A0std::string input_q, input_a;
>> > =A0 =A0 =A0 =A0while( ( c=3Dwgetch(quest_win) ) ){
>> > =A0 =A0 if ( (c =3D=3D 10) ){
>> > =A0 =A0 =A0 =A0def_prog_mode();
>> > =A0 =A0 =A0 =A0endwin();
>>
>> What are these?
>>
>> > =A0 =A0 =A0 =A0system(editor);
>> > =A0 =A0 =A0 =A0reset_prog_mode();
>>
>> and this?
>=20
> A gnu extension for building a filebuf from a file descriptor. IMO
> closing the fildescriptor returned and using a simple ifstream with
> path, would be less trouble.

Those above are part of ncures.h, but those below as was you describe.

>=20
> In particular, the openmode are not good: binary will not translate
> carriage return and app is irrelevant in input mode (and input mode is
> missing). Use plain std::ios::in instead.
>=20

The editor is creating a text file so you might be correct, but I don't
think I want carriage returns altered or interpreted, just eventually
dumped into a data file at 4096 bit clips.  And I don't want to deal
with deliminators or terminators on input, or output, which is a problem
with getline and getchar.  I want them included in the input stream,
whole.


> I don't know how it works in conccurent access, stdio_sync_filebuf<>
> may be required here (with minimal buffer size in parameter for good
> measure).
>=20

It didn't have trouble with two seperate streams from the same fd.  I
did have trouble using one stream for both in and out.

>> > =A0 =A0 =A0 =A0 __gnu_cxx::stdio_filebuf< =A0char> =A0 tmpfile_buf(f=
d, std::ios::binary|std::ios::app);
>>
>> What's one of those?
>>
>> > =A0 =A0 =A0 =A0 std::istream is(&tmpfile_buf);
>> > =A0 =A0 =A0 =A0 is.seekg(0, std::ios::beg);
>=20
> seekg is not guaranteed to work
>

Upon input?  It didn't work away.  I thought maybe I as set to the end
of the stream but it didn't like binary mode at all, and the eof bits
behaved as I expected so I can only guess that it was behaving OK.
=20
>> > =A0 =A0 =A0 =A0 while(is){
>> > =A0 =A0 =A0 =A0 =A0 =A0is.read( tmp, 4096);
>> > =A0 =A0 =A0 =A0 =A0 =A0std::cerr<< =A0"What did we read"<< =A0tmp<< =
=A0std::endl;
>> > =A0 =A0 =A0 =A0 =A0 =A0input_q =3D tmp;
>> > =A0 =A0 =A0 =A0 }
>> > =A0 =A0 =A0 =A0 tmpfile_buf.close();
>=20
> Note that you can dump the content of a file with:
>  std::err<<is.rdbuf();
>

I want a guaranteed chunk of 4096, no greater.
=20
>> > =A0 =A0 =A0 =A0 break;
>> > =A0 =A0 }
>> > =A0 =A0 =A0 =A0}
>> > =A0 =A0 =A0 =A0remove(path);
>>
>=20
> --
> Michael