C / C++ / MFC

11-Dec-13 1:16

Its too slow when I open -> write -> close a file (see code below).
Are they a way of opening the file and always writing at the top of the file; e.g. I do not want to Append text, just write the same 100 lines of text each time at the top of the file.

#include <stdio.h>
FILE * pFile;
/* open file and check if was successful */
if ((pFile = fopen("myfile.txt", "w")) == NULL)
{
/* couldn't open file; do some error handling if u want */
}
else
{
/* do s.th. */
/* close file */
fclose(pFile);
}

Waiting in hope!

grahamfff

Richard MacCutchan11-Dec-13 1:53

11-Dec-13 1:53

No, there is no way, since all the data that you write would overwrite whatever is already there. You would need to hold the data in memory, and rewrite all of it every time.

Veni, vidi, abiit domum

Grahamfff11-Dec-13 2:33

11-Dec-13 2:33

I just want to append to the TOP of the file each time. Its too slow doing an open -> write -> close.
In a 20 msec loop and sometimes two files need to hav data written to them.

No timing problems with the append, but this could result in large files if I do not overwirie.

grahamfff

Richard MacCutchan11-Dec-13 2:38

11-Dec-13 2:38

Grahamfff wrote:
I just want to append to the TOP of the file each time.

As I said before, you cannot do it; the system just does not work that way. Perhaps it would be better if you explained why you want to do this.

Veni, vidi, abiit domum

Grahamfff11-Dec-13 4:04

11-Dec-13 4:04

In a 20 msec loop and sometimes two files need to have data written to them and the open -> write -> close takes about 8-10 msec each and sometimes get an overrun.

grahamfff

Richard MacCutchan11-Dec-13 4:57

11-Dec-13 4:57

Then you need to work on your system design; you cannot change the laws of physics.

Veni, vidi, abiit domum

enhzflep11-Dec-13 4:58

enhzflep

11-Dec-13 4:58

As Eugen alludes to, a time-critical loop is not the place to muck about. Write the data to the end of the file then deal with the order later on.

Furthermore, I assume that you're dealing with different files each time through the loop. If not, then again, don't muck about. Open the file before the loop and close it again afterwards.

Eugen Podsypalnikov11-Dec-13 2:26

Eugen Podsypalnikov

11-Dec-13 2:26

// I do not want to Append text, just write the same 100 lines of text each time at the top of the file.

Any appending in the file context is more rapid than an inserting.
Of course, you could try to append the reversed content to be read later as reversed as well... Smile | :)

They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap. Smile | :)

David Crow11-Dec-13 5:15

David Crow

11-Dec-13 5:15

Grahamfff wrote:
Are they a way of opening the file and always writing at the top of the file;

Do you mean having the newest data at the beginning of the file (rather than at the end)?

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Show me a community that obeys the Ten Commandments and I'll show you a less crowded prison system." - Anonymous

Grahamfff11-Dec-13 5:22

11-Dec-13 5:22

Yes that would do!

They are recoverery data files, so periodically writing them. Just interested in the newest data.

grahamfff

Stefan_Lang15-Dec-13 23:23

Stefan_Lang

15-Dec-13 23:23

Grahamfff wrote:
They are recoverery data files,

Now, finally, you are providing some useful info.

First off, the file system is a bottleneck. The only way to speed up file access is use a different file system. But you probably don't have that choice.

Second, repeatedly writing to hard disk in a fixed time loop every 20ms is an incredibly stupid idea, for various reasons - this is simply not the intended purpose of a file system! You should consider different storage media, depending an what is available to you, or you should consider to just wait longer between writes. I'm not an expert on this, but Flash drives, SRAM, or even USB may be more suitable. (Although writing to flash drives 50 times per second is a sure way to destroy them in short order...)

Third, I can't think of any reason to write recovery info more often then once every couple of seconds: a recovery feature usually means the ability to restore a state that is difficult to reproduce, either because it is the result of interacting with a non-deterministic system (such as a human), or because there is no other way to reproduce the data (e. g. in very long range communication such as talking to mars rovers and the like). Either way, losing the data from as little a timespan as one second is meaningless! OTOH, if for whatever incomprehensible reason you really, really need that info stored every 0.02s flawlessly, then the file system simply is too slow to reliably do this - not to mention that trying it will slow your entire application to a crawl. As suggested above, use a different storage medium!

GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)

Alan Balkany11-Dec-13 5:27

Alan Balkany

11-Dec-13 5:27

Open the file as "read/update": fopen ("myfile.txt", "r+"), link: http://www.cplusplus.com/reference/cstdio/fopen/[^]

The use fseek (SEEK_SET) to position the file pointer to the beginning of the file. Link: http://www.cplusplus.com/reference/cstdio/fseek/[^]

You can then just overwrite 100 lines of text, without having to write the WHOLE file.

app for windows 8.1

Member 1045927510-Dec-13 22:32

Member 10459275

10-Dec-13 22:32

I want to make an windows 8.1 store app(can be desktop but prefer store).
I know the following languages :
visual basic 2012(win rt)(mostly preferable)
visual c++( not so good)

i have to make the beta fast Frown | :-(

PROGRAM:-
->a interactive full screen homepage with 3 buttons and settings in the charm bar

HOME PAGE buttons:-
->1st button: record screen: records the desktop and other win 8 apps with webcam support and audio from mic

->2nd button: Edit video: more like mixing. you can drag-drop video to timeline(like windows movie maker) and 2 channel audio(one for voice and one for song)

->3rd button: upload video: push the video to the web as mp4 or avi at youtube or facebook or save them to disk

VOICE RECOGNITION:-
(optional) at the home screen when user say some command like 'program run record' or 'program edit video', the program does the same.

i want some leads...i have no experience in intensive, professional programming but i want to do so.
i would really appreciate if you tell me what i have to do,
specifically:
things that are easy,
things that need some stress
and work on!

Thanks in advance

Re: app for windows 8.1

Richard MacCutchan11-Dec-13 0:23

11-Dec-13 0:23

I would suggest you go to the articles section here[^] and look for articles on the subjects that you need to learn. You can also use Google for wider searches.

Veni, vidi, abiit domum

Re: app for windows 8.1

Erudite_Eric11-Dec-13 1:57

Erudite_Eric

11-Dec-13 1:57

tell your boss to hire someone who can.

Get rid of STL warnings

_Flaviu10-Dec-13 21:58

_Flaviu

10-Dec-13 21:58

I had compiled MFC Grid control 2.27[^] project, but I get a lot of warnings (I use VC6):

C++

GridCell.cpp
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xmemory(39) : warning C4100: '_P' : unreferenced formal parameter
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xmemory(41) : warning C4100: '_P' : unreferenced formal parameter
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\vector(249) : warning C4663: C++ language change: to explicitly specialize class template 'vector' use the following syntax:
        template<> class vector<bool,class std::allocator<unsigned int> > ...
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\vector(156) : warning C4018: '<' : signed/unsigned mismatch
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\vector(156) : while compiling class-template member function 'void __thiscall std::vector<unsigned int,class std::allocator<unsigned int> >::insert(unsigned int *,unsigned int,const unsig
ned int &)'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\vector(167) : warning C4018: '<' : signed/unsigned mismatch
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\vector(156) : while compiling class-template member function 'void __thiscall std::vector<unsigned int,class std::allocator<unsigned int> >::insert(unsigned int *,unsigned int,const unsig
ned int &)'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xmemory(37) : warning C4100: '_P' : unreferenced formal parameter
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\xmemory(68) : see reference to function template instantiation 'void __cdecl std::_Destroy(unsigned int *)' being compiled

and so on ... I had tried
#pragma warning(disable 4100) ... doesn't have any affect ...

How can I get rid of this warnings ? Thank you.

Richard MacCutchan10-Dec-13 22:23

10-Dec-13 22:23

Looking at thos messages suggests that you are using a very old version of Visual Studio. You probably need to upgrade to a later version.

Veni, vidi, abiit domum

Freak3010-Dec-13 23:01

Freak30

10-Dec-13 23:01

You could either set the warning level for the whole project to 3 in the settings.

Or you can include the line
#pragma warning(disable 4100)
in you Stdafx.h file before the relevant includes.

Or if you don't want to do this, you can wrap the MFC includes in the following:
#pragma warning (push, 3)
#include "whatever"
#pragma warning (pop)

The good thing about pessimism is, that you are always either right or pleasently surprised.

_Flaviu11-Dec-13 2:37

_Flaviu

11-Dec-13 2:37

I had tried to put

C++

#pragma warning(disable 4100)

in stdafx.h, but doesn't work ... I'll try other one ...

Trying to reuse code with a static library

David Crow11-Dec-13 5:19

David Crow

11-Dec-13 5:19

I seem to recall a yvals.h file. Try here for starters.

Richard Andrew x648-Dec-13 19:21

Richard Andrew x64

8-Dec-13 19:21

I'm trying to put reusable code into a static library and link it into a couple of different projects.

The problem is that while linking one of the projects that's supposed to use the reusable code, it reports all sorts of multiply defined symbols. (See below)

The main projects use DLL versions of the C-runtime, and the static library is set to use the multi-threaded dll version also.

What's the trick to successfully linking a static library into multiple projects?
(If I haven't provided enough info, just ask.)

Multiply defined symbols messages:
(Is this happening because the C-runtime is linked into the static lib first, and then those symbols are conflicting with the symbols in the main project?)

5>LIBCMTD.lib(dbgheap.obj) : error LNK2005: __CrtSetCheckCount already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(dbgheap.obj) : error LNK2005: __calloc_dbg already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(invarg.obj) : error LNK2005: __invoke_watson already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(sprintf.obj) : error LNK2005: _sprintf already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(dbghook.obj) : error LNK2005: __crt_debugger_hook already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0dat.obj) : error LNK2005: __amsg_exit already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0dat.obj) : error LNK2005: __cexit already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0dat.obj) : error LNK2005: __exit already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0dat.obj) : error LNK2005: __initterm_e already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0dat.obj) : error LNK2005: _exit already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(wsetloca.obj) : error LNK2005: __configthreadlocale already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(swprintf.obj) : error LNK2005: _swprintf_s already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(mlock.obj) : error LNK2005: __lock already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(mlock.obj) : error LNK2005: __unlock already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(winapisupp.obj) : error LNK2005: ___crtGetShowWindowMode already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(winapisupp.obj) : error LNK2005: ___crtSetUnhandledExceptionFilter already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(winapisupp.obj) : error LNK2005: ___crtTerminateProcess already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(winapisupp.obj) : error LNK2005: ___crtUnhandledException already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(winxfltr.obj) : error LNK2005: __XcptFilter already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(vsnprnc.obj) : error LNK2005: __vsnprintf_s already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(hooks.obj) : error LNK2005: "void __cdecl terminate(void)" (?terminate@@YAXXZ) already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(crt0init.obj) : error LNK2005: ___xi_a already defined in msvcrtd.lib(cinitexe.obj)
5>LIBCMTD.lib(crt0init.obj) : error LNK2005: ___xi_z already defined in msvcrtd.lib(cinitexe.obj)
5>LIBCMTD.lib(crt0init.obj) : error LNK2005: ___xc_a already defined in msvcrtd.lib(cinitexe.obj)
5>LIBCMTD.lib(crt0init.obj) : error LNK2005: ___xc_z already defined in msvcrtd.lib(cinitexe.obj)
5>LIBCMTD.lib(vswprnc.obj) : error LNK2005: __vsnwprintf_s already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(dbgrptw.obj) : error LNK2005: __CrtDbgReportW already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(printf.obj) : error LNK2005: _printf already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(errmode.obj) : error LNK2005: ___set_app_type already defined in msvcrtd.lib(MSVCR120D.dll)
5>LIBCMTD.lib(towlower.obj) : error LNK2005: _towlower already defined in msvcrtd.lib(MSVCR120D.dll)
5>LINK : warning LNK4098: defaultlib 'msvcrtd.lib' conflicts with use of other libs; use /NODEFAULTLIB:library
5>LINK : warning LNK4098: defaultlib 'LIBCMTD' conflicts with use of other libs; use /NODEFAULTLIB:library

The difficult we do right away...
...the impossible takes slightly longer.

Re: Trying to reuse code with a static library

Richard MacCutchan8-Dec-13 22:24