Is main() a callback function?

Lost User

No, it is just a function that gets called by the run-time library, framework etc. I have a feeling (vague memory) that you can tell the linker to use some other function as the starting point, but don't know why you would want to.

OriginalGriff

Probably not:

Callback (computer programming) - Wikipedia[^]

a callback, also known as a "call-after"[1] function, is any executable code that is passed as an argument to other code that is expected to call back (execute) the argument at a given time.

So to be a callback function it would need to be passed as an argument to some other function, and I can't see any good reason to do that when you can call it directly or via a function pointer / function table that is set by the compiler / linker. That you can't call main at all except from a single point in your app kinda backs that up as well!

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OriginalGriff

Richard MacCutchan wrote:

don't know why you would want to

To annoy the next poor developer that has to work on your satan-spawned code ... :laugh:

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Rob Philpott

Interesting, I didn't know/have forgotten about the re-entrancy. Seems you can do it in C#, but that's with a capital 'M'ain, and is a language for wimps.

Regards, Rob Philpott.

Rob Philpott

Yes, but I kind of expect the OS to call my method at the given time of the process starting up...? And the address is passed to the OS to be called back on, just through an extra layer of module EXPORTS etc. It's a pedant's dream this. I should move on.

Regards, Rob Philpott.

Rick York

I couldn't agree more.

"They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

DRHuff

Well it never called me back - and I thought we had such a connection... :(( :(( :mad: :(( :((

I, for one, like Roman Numerals.

Rick York

The non-re-entrancy part comes about because you can't call it yourself. It's not a callback in the strict sense of the term but in effect it is if you think of it as the designated function for the OS to call to run the program. It is not specified in code (this is why it fails the strict definition) but it is implicitly known to the linker and can be overridden. In the case of programs for Windows, it IS overridden to be WinMain.

"They have a consciousness, they have a life, they have a soul! Damn you! Let the rabbits wear glasses! Save our brothers! Can I get an amen?"

OriginalGriff

The OS doesn't call your main method at all - there are three places it can start: the MZ Stub (which for Windows apps will just print "this program cannot be run in MSDOS mode" and quit the app), the NE or (for more modern apps) the PE: Portable Executable - Wikipedia[^]. And EXE files (even old MSDOS 16 bit apps) don't call main immediately anyway, they do allocation and static initialisation before they are ready to start running the code you wrote!

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony AntiTwitter: @DalekDave is now a follower!

PIEBALDconsult

It probably depends on the language, compiler, system, etc. As far as I know, in the languages I use, there nothing special about call-back functions, it's only about how an ordinary function is used. There's no reason to declare that no language will ever allow it. I seem to recall having a desire for a recursive main. : ) Just because.

Gary Wheeler

Rob Philpott wrote:

C# ... is a language for wimps

To quote my elderly cat, "Fight me, bitch."

Software Zen: delete this;

OriginalGriff

It called me back once, but it was drunk at the time.

"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony AntiTwitter: @DalekDave is now a follower!

Rob Philpott

It's how I express my intent daily to my ungrateful computer - I'm hooked, but its still the kid's soft play of computer languages. :-D

Regards, Rob Philpott.

ZurdoDev

How dare you ask programming questions in the lounge?!! I'm outraged. :mad:

Social Media - A platform that makes it easier for the crazies to find each other. Everyone is born right handed. Only the strongest overcome it. Fight for left-handed rights and hand equality.

Rob Philpott

Yeah, it's good to be reckless sometimes. Send me the codez and I'll go away. :)

Regards, Rob Philpott.

Rob Philpott

That reminds me of a thing I read some time back, titled something along the lines of 'the 50 things Windows does before hitting main()'. Can't find it but it's out there somewhere, by one of the SysInternals lot I think. It was both interesting and really boring at the same time.

Regards, Rob Philpott.

Lost User

Rick York wrote:

you can't call it yourself.

Indeed you can, but you need to know what you are doing.

Rick York wrote:

but it is implicitly known to the linker

Not quite, there is a reference to it in the run time libraries which must be satisfied at link time.

Rick York wrote:

in the case of programs for Windows, it IS overridden to be WinMain.

But there is a main() inside the Windows libraries, which again gets called by the run time (unless it has changed in the last 20+ years). And that then calls in to WinMain.

honey the codewitch

C is for wimps Real programmers use butterflies

Real programmers use butterflies

DRHuff

Did it say - "I want to C you again!" ? And did you reply #ly that you had moved on? :-D

I, for one, like Roman Numerals.

honey the codewitch

I figure every function is a callback function - it's just a matter of perspective. :-D

Real programmers use butterflies