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cargumentsprogram-entry-pointargvargc
Deanie
Deanie

Reputation: 2385

Are there any other arguments that main() can accept?

I recently came across the following in my searches regarding environment variables in C:

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

I have searched around and can't find anything conclusive regarding my question.

What are all of the available arguments that main() can accept?

Upvotes: 5

Views: 1132

Answers (2)

Shafik Yaghmour
Shafik Yaghmour

Reputation: 158469

The C99 and C11 draft standards allow for implementation defined set of parameters to main, these parameters are going to be specific to those systems(non-portable). From section 5.1.2.2.1:

[...]or in some other implementation-defined manner[...]

The only additional parameters I can find documented are envp and apple, we can find a good description in Wikipedia's C and C++ section on Entry Points:

Other platform-dependent formats are also allowed by the C and C++ standards, except that in C++ the return type must always be int;[6] for example, Unix (though not POSIX.1) and Microsoft Windows have a third argument giving the program's environment, otherwise accessible through getenv in stdlib.h:

int main(int argc, char **argv, char **envp);

Mac OS X and Darwin have a fourth parameter containing arbitrary OS-supplied information, such as the path to the executing binary:[7]

int main(int argc, char **argv, char **envp, char **apple);

It looks like Windows has a Microsoft specific wmain which takes wchar_t:

int wmain(int argc, wchar_t *argv[], wchar_t *envp[]);

Upvotes: 10

Dai
Dai

Reputation: 155145

The alternative is the wide-character version:

int main(int argc, wchar_t* argv[], wchar_t* envp[])

The main function is specified in the language specification as the following, no other function signature is provided besides a get-out clause for implementation-specific entrypoint functions (like Apple's 3rd apple parameter) or Microsoft's WinMain function.

5.1.2.2.1 Program startup

The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters:

int main(void) { /* ... */ }

or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):

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

or equivalent or in some other implementation-defined manner. If they are declared, the parameters to the main function shall obey the following constraints:

  • The value of argc shall be nonnegative.
  • argv[argc] shall be a null pointer.
  • If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup. The intent is to supply to the program information determined prior to program startup from elsewhere in the hosted environment. If the host environment is not capable of supplying strings with letters in both uppercase and lowercase, the implementation shall ensure that the strings are received in lowercase.
  • If the value of argc is greater than zero, the string pointed to by argv[0] represents the program name argv[0][0] shall be the null character if the program name is not available from the host environment. If the value of argc is greater than one, the strings pointed to by argv[1] through argv[argc-1] represent the program parameters.
  • The parameters argc and argv and the strings pointed to by the argv array shall be modifiable by the program, and retain their last-stored values between program startup and program termination.

Upvotes: 3

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