Significance of main()

[Alse]

Hi, I would like to know what is the significance of main( ) in C/C++ programs?
Even though it is a user defined function, it is not as flexibile as other user defined function?

[Tim Garrett]

Hi, I would like to know what is the significance of main( ) in C/C++ programs?
Even though it is a user defined function, it is not as flexibile as other user defined function?

Its a user defined function, but the declaration is part of the C run time. As your program begins to execute, its doing a whole lot of stuff to initialise the process to the point where your code can execute. Once the initialisation is complete (DLLs loaded, memory allocated etc) it calls main(). It expects an integer return, which is passed back the OS. Its defaulted to zero so you don't have to bother if you don't want to.

[Banfa]

Its defaulted to zero so you don't have to bother if you don't want to.

This isn't right, since main returns int most compilers will issue an error if you do not return int from the function therefore you always have to bother to return a value.

[Tim Garrett]

This isn't right, since main returns int most compilers will issue an error if you do not return int from the function therefore you always have to bother to return a value.

Stroustrup 3rd Ed Section 3.2...
The minimal C++ program is...
int main() {}

[Alse]

In simple words i can say it is the starting point. Hence it is must to specify the starting point for any program.

Thanks to all
Alse

[JosAH]

Stroustrup 3rd Ed Section 3.2...
The minimal C++ program is...
int main() {}

Yes, C++ differs from C in that: returning an int value is optional while it isn't
in C. The main method also can't be called recursively in C++ while it can in C.
In C++ main is more 'special' than it is in C. Microsoft's convention of defining
main (in either C or C++) as a void function is a big nono.

kind regards,

Jos

[Banfa]

In C++ main is more 'special' than it is in C. Microsoft's convention of defining main (in either C or C++) as a void function is a big nono.

I don't think that this a Microsoftism, I haven't see it said anywhere before that it is OK to return void from main. Although checking the help they do not seem to specify the return type at all.

What MS does do as an extention is put a 3 parameter in main containing the environment it was called with.

I have seen compilers that allow void main (specifically mcc18 PIC compiler) but this was strictly as an extension.

[JosAH]

I don't think that this a Microsoftism, I haven't see it said anywhere before that it is OK to return void from main. Although checking the help they do not seem to specify the return type at all.

What MS does do as an extention is put a 3 parameter in main containing the environment it was called with.

I have seen compilers that allow void main (specifically mcc18 PIC compiler) but this was strictly as an extension.

In this link Microsoft states this:

Alternatively, the main and wmain functions can be declared as returning void
(no return value). If you declare main or wmain as returning void, you cannot
return an exit code to the parent process or operating system using a return
statement; to return an exit code when main or wmain is declared as void, you
must use the exit function.

Microsoft have been doing this for years; even when the first ISO C draft was
out of the bag Microsoft continued writing 'void main' and a lot of people believed
it was correct (which it isn't according to the Standard).

kind regards,

Jos

[Banfa]

In this link

Interesting, you just can't trust em can you :rolleyes:

That paragraph does not appear in the help files supplied with MSVC++

At the very least it should be tagged as a MS extension.

[JosAH]

Interesting, you just can't trust em can you :rolleyes:

That paragraph does not appear in the help files supplied with MSVC++

At the very least it should be tagged as a MS extension.

Well, to be honest they do: that void main thing is discussed in the paragraph
titled: "END Microsoft Specific" ;-) they use it all over the place themselves
which renders their own code non-Standard and non-portable.

kind regards,

Jos

[Banfa]

Well, to be honest they do: that void main thing is discussed in the paragraph
titled: "END Microsoft Specific";

Erm, yes this puts it outside Microsoft Specific stuff which is

Microsoft Specific

in this section here

END Microsoft Specific

So they are claiming that is how C/C++ works not that is how there implementation works.

... they use it all over the place themselves
which renders their own code non-Standard and non-portable.

Would you want to port it? (I'm being flipant, I do get the point)

I have to say one of the things I enjoy about embedded programming is that MS doesn't feature.

[JosAH]

Erm, yes this puts it outside Microsoft Specific stuff which is

Microsoft Specific

in this section here

END Microsoft Specific

So they are claiming that is how C/C++ works not that is how there implementation works.

Would you want to port it? (I'm being flipant, I do get the point)

I have to say one of the things I enjoy about embedded programming is that MS doesn't feature.

I don't even want to be found dead porting anything to or from a Microsoft OS.
IMHO what Microsoft has done and still is doing is a major setback for the
entire computing industry. But I guess that's what monopolies are for ;-)

kind regards,

Jos

ps. I especially like unhosted embedded programming, i.e. you can be king
over that poor little processor ;-)