c - Return type of main function -

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possible duplicate:
what should main() return in c/c++?
difference between void main , int main?

i have been using main method in c 

void main(){ // code }

and works pretty me. know other int return type:

int main(void) int main() int main(int argc, char *argv[])

but have not been able find resource says can use void return type. every book suggests return type must int or else omitted. why void main() work?

is dependent on version of c using? or work because use c++ ide? please reply specific c , not c++.

only book authors seem privy place return type of void main() allowed. c++ standard forbids completely.

the c standard says standard forms are:

int main(void) { ... }

and

int main(int argc, char **argv) { ... }

allowing alternative equivalent forms of declaration argument types (and names discretionary, of course, since they're local variables function).

the c standard make small provision 'in other implementation defined manner'. iso/iec 9899:2011 standard says:

5.1.2.2.3 program termination

if return type of main function type compatible int, return initial call main function equivalent calling exit function value returned main function argument;11) reaching } terminates main function returns value of 0. if return type not compatible int, termination status returned host environment unspecified.

11) in accordance 6.2.4, lifetimes of objects automatic storage duration declared in main have ended in former case, not have in latter.

this allows non-int returns, makes clear not specified. so, void might allowed return type of main() implementation, can find documentation.

(although i'm quoting c2011 standard, same words in c99, , believe c89 though text @ office , i'm not.)

incidentally, appendix j of standard mentions:

j.5 common extensions

the following extensions used in many systems, not portable implementations. inclusion of extension may cause strictly conforming program become invalid renders implementation nonconforming. examples of such extensions new keywords, library functions declared in standard headers, or predefined macros names not begin underscore.

j.5.1 environment arguments

in hosted environment, main function receives third argument, char *envp[], points null-terminated array of pointers char, each of points string provides information environment execution of program (5.1.2.2.1).

why void main() work?

the question observes void main() works. 'works' because compiler best generate code programs. compilers such gcc warn non-standard forms main(), process them. linker isn't worried return type; needs symbol main (or possibly _main, depending on system) , when finds it, links executable. start-up code assumes main has been defined in standard manner. if main() returns startup code, collects returned value if function returned int, value garbage. so, sort of seems work long don't exit status of program.


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