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Jul 18th, 2007

why return an int from main?

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i hope that this does not sound like a silly question but can someone please tell me why we return an integer from the main method in c++?

if program execution starts and ends in main then what is the point? main calls other mothods and receive return types so why does main have to return something itself?

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quintoncoert

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Jul 18th, 2007

Re: why return an int from main?

have a look at these links here -

http://users.aber.ac.uk/auj/voidmain.shtml
http://faq.cprogramming.com/cgi-bin/...&id=1043284376
http://www.parashift.com/c++-faq-lit....html#faq-29.3

Last edited by Bench; Jul 18th, 2007 at 7:16 am.

Bench

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Jul 18th, 2007

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Re: why return an int from main?

Historically,
- C++ was derived from C.
- In C, everything was an int unless specified otherwise (there was no void), so it was natural for main to return int.
- C programs were originally developed for command line use, and using a command line interpreter which was far more capable 30 years ago than M$ cmd.exe is even today. That command interpreter could easily determine whether the program just ran was a success (or not) from the value returned by main.

Salem

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Jul 18th, 2007

Re: why return an int from main?

I always learned that main returns an int so that you can put exit(0), exit(1) and other constructions in to tell you why the program quit. Or would that not work...?

venomlash

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Jul 19th, 2007

Re: why return an int from main?

yup. The code is returned to the operating system and can be polled from other programs (like shellscripts) to determine the reason why the program terminated (with 0 traditionally indicating that everything worked smoothly).

jwenting

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duckman

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Jul 20th, 2007

Re: why return an int from main?

Click to Expand / Collapse Quote originally posted by venomlash ...

I always learned that main returns an int so that you can put exit(0), exit(1) and other constructions in to tell you why the program quit. Or would that not work...?

Interesting question, to rephrase:
If i have a void main() and in the code I write exit(11). When I call this program from command line what will be return code of it?

thekashyap

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Jul 20th, 2007

Re: why return an int from main?

You're still wrong even if your only way out is via exit()
http://c-faq.com/ansi/voidmain3.html

Salem

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Jul 20th, 2007

Re: why return an int from main?

Some compilers will even let you declare main as returning a pointer! (VC++ 6.0 for example)

C++ Syntax (Toggle Plain Text)
char* main()
{
   char* ptr;
   return ptr;
}
char* main()
{
   char* ptr;
   return ptr;
}

But since pointers are really integers the program will actually return the integer value of that pointer. Meaningless -- absolutely. But I've seen someone try to do it.

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Jul 20th, 2007

Re: why return an int from main?

Click to Expand / Collapse Quote originally posted by quintoncoert ...

if program execution starts and ends in main then what is the point? main calls other mothods and receive return types so why does main have to return something itself?

Like others have said, main's return value is used to determine if the program ran successfully or what the errors were. As to why the mechanism is a return value, when your program runs, something in your OS is calling main. When your program finishes, main returns an int to the OS function which called it.

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Jul 23rd, 2007

Re: why return an int from main?

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

Some compilers will even let you declare main as returning a pointer! (VC++ 6.0 for example)
C++ Syntax (Toggle Plain Text)
char* main()
{
   char* ptr;
   return ptr;
}
char* main() { char* ptr; return ptr; }

I tried it on VC5 and it failed?

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