C / C++ / MFC

Mircea Neacsu14hrs 52mins ago

14hrs 52mins ago

The chain of include files can be long and tortuous. In this particular case:
iostream -> istream -> ostream -> ios -> cstdio -> stdio.h

Should you rely on compiler include chains? Depends if you expect your code to be compiled with a different compiler and how long the chain is. In this particular case, there is a strong probability that all C++ iostream operations will end up like C function calls so you are pretty safe.

Mircea

mike74114hrs ago

mike7411

4hrs ago

I'm looking at the ios file, and I don't see where cstdio gets included.

I did a search in the file for cstdio, and it doesn't seem to be there.

Thanks.

Mircea Neacsu3hrs 41mins ago

3hrs 41mins ago

I skipped a step: ios -> xlocnum -> cstdio.

Mircea

Victor Nijegorodov14hrs 51mins ago

Victor Nijegorodov

14hrs 51mins ago

mike7411 wrote:
It works if I do this:
C++
include <iostream>

Any idea why this works?

I guess, because there is a declaration of printf or or this is #included

k505414hrs 21mins ago

k5054

14hrs 21mins ago

iostream provides very complex facilities to C++, and requires a great deal of supporting infrastructure. You can get a list of all the include files that a compilation unit needs by using the /showIncludes flag in your compiles (-H for gcc/clang). Using Compiler Explorer, I see over 100 additional files included, including new, string, istream, ostream, atomic and cstdio (which gets you printf), just to name a few. As others have pointed out, you can just go ahead and use printf for example, and not add #include <cstdio> to your source file. However, as compilers evolve, you may find that this is no longer the case, at which point your code will fail to compile. Its good practice to #include all the relevant headers. System headers, at least, will have guards against multiple inclusions, so there's no harm in being explicit about what headers your program, or module, requires.

"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown

copying a file

mike741116hrs 59mins ago

mike7411

16hrs 59mins ago

Can someone tell me if this code works to copy a binary file?

while ((ch = fgetc(source)) != EOF) {
        fputc(ch, target);
    }

What if the file contains a byte that is 255?
Won't it get converted to -1 and break the loop?

Thank you.

Re: copying a file

Mircea Neacsu16hrs 51mins ago

16hrs 51mins ago

Depends on declaration of ch. If it’s an int (as it should), all is fine as 255 != -1. If it’s char, it fails, with or without compiler warnings.

Mircea

Re: copying a file

Richard MacCutchan16hrs 18mins ago

16hrs 18mins ago

You should not use fgetc, fgets, or any other character based function to process binary files. You should use fread | Microsoft Learn[^] and fwrite | Microsoft Learn[^].

Re: copying a file

k505415hrs 41mins ago

k5054

15hrs 41mins ago

While your method may work, assuming that ch is an int, and so does not have the 255/-1 issue, your method is horribly inefficient. Richard's suggestion to use fread/fwrite produces much better performance.

For example, given an 8M file, looping through your code 100 times took about 32 seconds. Using a fread/fwrite using a 4K buffer, the same 100 lops took just under 1 second to complete. This was on a PI-3, and successive runs remained stable. I'd expect an 8M file to sit comfortably in the file cache, so the difference is totally down to the difference between extracting a single char at a time, and reading a lot of characters at a time.

"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown

Myth of a Myth?

jschell4-Dec-23 4:38

jschell

4-Dec-23 4:38

From CP newsletter

The Myth of Smart Pointers – Logikal Blog[^]

Basically complaining about what unique_ptr<t> is defined as.

Myself reading it and looking at the code it seems to me that the author does not understand the difference between the C++ specification and the C++ compiler/runtime.

Which has always been a problem for some people using C/C++ pointers since C (before C++ existed.)

The author seems to be suggesting that the specification is guaranteeing that the memory will be collected. But without even reading the spec I seriously doubt it says that. I suspect it is noting that the it might be collected so one should not rely on it.

There are multiple other places where one can do similar things and it might or might not work depending on compiler, binary and even execution flow (which is really fun to debug.)

Perhaps I am mistaken in what I am reading?

Re: Myth of a Myth?

Richard MacCutchan4-Dec-23 5:57

4-Dec-23 5:57

Given the fact that he is breaking all the rules by branching off into QML (whatever that is, and by his own comments something to be avoided) and Javscript, then you cannot expect C++ to know what is happening outside.

Re: Myth of a Myth?

Mircea Neacsu4-Dec-23 6:05

how to add another primary menu - C + in Qt

4-Dec-23 6:05

jschell wrote:
The author seems to be suggesting that the specification is guaranteeing that the memory will be collected. But without even reading the spec I seriously doubt it says that. I suspect it is noting that the it might be collected so one should not rely on it.

Of course it doesn't guarantee. Where the memory is coming from and where it is going to, is outside the scope of the language specification. From C++11 to C++23 there was some kind of support for garbage collection using std::declare_reachable, but it was deleted[^].

Mircea

Salvatore Terress1-Dec-23 7:34

Salvatore Terress

1-Dec-23 7:34

Voluntarily removed - posted in wrong forum...

modified 2 days ago.

Re: how to add another primary menu - C + in Qt

Andre Oosthuizen1-Dec-23 23:18

Andre Oosthuizen

1-Dec-23 23:18

37 Questions asked in 2 months starts leaning towards a "Help Vampire". You have not shown us in your code above what you have tried apart from 4 lines of code, which oddly looks AI generated. Please tell us what you have researched so far on how to add second primary menus. If this errors, show the error and we will gladly assist from there.

Re: how to add another primary menu - C + in Qt

Richard MacCutchan1-Dec-23 23:22

1-Dec-23 23:22

A number of previous incarnations, one of which was at Discussions - Linux Programming Discussion Boards[^]

Invalidate rectangle

Calin Negru1-Dec-23 1:41

Calin Negru

1-Dec-23 1:41

I’m trying to display an animated bitmap in a win32 application with GDIplus. Last time when I talked about this here I was told I should invalidate a rectangle to force the App to refresh/draw another frame. I’m trying to understand the theory for now. I will come up with code in a day or two if necessary. My question is do you create and invalidate between beginpaint and endpaint a rectangle that has no particular purpose or does it have to be a rectangle that actually does something.
I’m having a difficult time understanding the connection between a rectangle and the rendering process of a win32 api window

CPallini1-Dec-23 2:01

CPallini

1-Dec-23 2:01

Roughly speaking, the invalidated rectagle will be redrawn in the next WM_PAINT call (other parts of the client area are not redrawn). So, if you need to update a portion of the client area then invalidate the corresponding rectangle and then call UpdateWindow().
In simple scenarios you can invalidate the entire client area and then call UpdateWindow().
See, for instance: Invalidating the Client Area - Win32 apps | Microsoft Learn[^].

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Calin Negru1-Dec-23 2:40

Calin Negru

1-Dec-23 2:40

Basically I need a rectangle taking the whole window for my game, I think I understand, I’ll post a followup if I’ll run into trouble setting things. Thank you.

CPallini1-Dec-23 2:56

CPallini

1-Dec-23 2:56

You are welcome.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Richard MacCutchan1-Dec-23 3:13

1-Dec-23 3:13

The only things you should be doing between BeginPaint and EndPaint is redrawing/rewriting the parts of the client window that may have changed. Outside of the WM_PAINT handler, you decide which part (or all) of the window needs to be repainted. You then set those values into a call to InvalidateRect, which will post a WM_PAINT message to your message queue.

Calin Negru1-Dec-23 4:55

Calin Negru

1-Dec-23 4:55

>The only things you should be doing between beginpaint and endpaint

I was thinking to disregard everything that was rendered in one frame, and then render things all over again. Keeping track of pieces that visually change in my game ( if that’s what you mean) seems like a burden at this point.
So far I’m only looking for a way to trigger a new paint event

modified 3 days ago.

Richard MacCutchan1-Dec-23 5:28