What is the proper declaration of main in C

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What is the proper signature of the main function in C++?
What is the correct return type, and what does it mean to return a value from main?
What are the allowed parameter types, and what are their meanings?
Is this system-specific?
Have those rules changed over time?
What happens if I violate them?

User · Answer

Details on return values and their meaning Per 3 6 1   basic start main     A return statement in main has the effect of leaving the main function  destroying any objects with automatic storage duration  and calling std  exit with the return value as the argument  If control reaches the end of main without encountering a return statement  the effect is that of executing return 0    The behavior of std  exit is detailed in section 18 5   support start term    and describes the status code   Finally   control is returned to the host environment    If  status is zero or EXIT SUCCESS  an implementation-defined form of the status successful termination is returned  If status is EXIT FAILURE  an implementation-defined  form of the status unsuccessful termination is returned   Otherwise the status returned is implementation-defined

User · Answer

The two valid mains are int main   and int main int  char      Any thing else may or may not compile  If main doesn t explicitly return a value  0 is implicitly returned

User · Answer

The main function must be declared as a non-member function in the global namespace   This means that it cannot be a static or non-static member function of a class  nor can it be placed in a namespace  even the unnamed namespace      The name main is not reserved in C   except as a function in the global namespace   You are free to declare other entities named main  including among other things  classes  variables  enumerations  member functions  and non-member functions not in the global namespace   You can declare a function named main as a member function or in a namespace  but such a function would not be the main function that designates where the program starts   The main function cannot be declared as static or inline   It also cannot be overloaded  there can be only one function named main in the global namespace   The main function cannot be used in your program  you are not allowed to call the main function from anywhere in your code  nor are you allowed to take its address   The return type of main must be int   No other return type is allowed  this rule is in bold because it is very common to see incorrect programs that declare main with a return type of void  this is probably the most frequently violated rule concerning the main function    There are two declarations of main that must be allowed   int main                     1  int main int  char           2    In  1   there are no parameters     In  2   there are two parameters and they are conventionally named argc and argv  respectively   argv is a pointer to an array of C strings representing the arguments to the program  argc is the number of arguments in the argv array     Usually  argv 0  contains the name of the program  but this is not always the case   argv argc  is guaranteed to be a null pointer   Note that since an array type argument  like char     is really just a pointer type argument in disguise  the following two are both valid ways to write  2  and they both mean exactly the same thing   int main int argc  char  argv    int main int argc  char   argv    Some implementations may allow other types and numbers of parameters  you d have to check the documentation of your implementation to see what it supports   main   is expected to return zero to indicate success and non-zero to indicate failure   You are not required to explicitly write a return statement in main     if you let main   return without an explicit return statement  it s the same as if you had written return 0    The following two main   functions have the same behavior   int main       int main     return 0      There are two macros  EXIT SUCCESS and EXIT FAILURE  defined in  lt cstdlib gt  that can also be returned from main   to indicate success and failure  respectively   The value returned by main   is passed to the exit   function  which terminates the program   Note that all of this applies only when compiling for a hosted environment  informally  an environment where you have a full standard library and there s an OS running your program    It is also possible to compile a C   program for a freestanding environment  for example  some types of embedded systems   in which case startup and termination are wholly implementation-defined and a main   function may not even be required   If you re writing C   for a modern desktop OS  though  you re compiling for a hosted environment

User · Answer

From Standard docs   3 6 1 2 Main Function      It shall have a return   type of type int  but otherwise its type is implementation-defined  All implementations shall allow both of the following   definitions of main    int main               and int main int argc  char  argv                    In the latter form argc shall be the number of arguments passed to the program from the environment in which the   program is run If argc is nonzero these arguments shall be supplied in argv 0  through argv argc-1  as pointers to   the initial characters of null-terminated multibyte strings        Hope that helps

User · Answer

The exact wording of the latest published standard (C++14) is:

An implementation shall allow both

a function of () returning int and

a function of (int, pointer to pointer to char) returning int

as the type of main.

This makes it clear that alternative spellings are permitted so long as the type of main is the type int() or int(int, char**). So the following are also permitted:

int main(void)
auto main() -> int
int main ( )
signed int main()
typedef char **a; typedef int b, e; e main(b d, a c)

[c++] What is the proper declaration of main in C++?

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