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For my class I need to create a function that takes in multiple parameters at runtime:

void main(int x, int y, int generation, char *layout[20])

However when the program runs with my input for these variables the information is not stored and in the debugging process 

run 3 3 3 Test_Round
print x // returns 5
print y // returns -8779

How do I pass multiple arguments into the main function so main will recognize the parameters I give it?

Thanks everyone! I just used argv[1] and so on to get the proper data I need!

alk
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Ilya Methot
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  • Does your implementation support this type of main function? – 2501 Jan 28 '17 at 16:34
  • I assume it does since it compiles and only gives warnings. – Ilya Methot Jan 28 '17 at 16:40
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    You should check the documentation. – 2501 Jan 28 '17 at 16:41
  • @IlyaMethot That's a bad assumption. The C standard never requires an error. In many cases, wrong code doesn't have to be diagnosed at all; and if it has to be diagnosed, a warning is enough. Don't ignore warnings. – melpomene Jan 28 '17 at 16:45
  • See also http://stackoverflow.com/questions/9242415/passing-arguments-to-main?rq=1. – melpomene Jan 28 '17 at 16:46
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    `main` should *always* be defined as `int main(int argc, char **argv)`. If you invoke your program as `my_program 123 456 789`, when main is entered argc will be 4, argv[0] will point to a character array containing "my_program\0", argv[1] will point to a character array containing "123\0", argv[2] will point to a character array containing "456\0", and argv[3] will point to a string containing (you guessed it!) "789\0". – Bob Jarvis - Слава Україні Jan 28 '17 at 16:48
  • Ah ok, so in this way I can read the input information and store it into variables. – Ilya Methot Jan 28 '17 at 16:50

3 Answers3

6

The standard is clear about how you need to declare your main function.

From the C99 Standard:

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;9) 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.

Meninx - メネンックス
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1
 void main(int x, int y, int generation, char *layout[20])

is an invalid signature of main(). You need to use

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

where, argv[0] to argv[argc-1] will hold the parameters passed to main().

Quoting C11, chapter §5.1.2.2.2,

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.

Sourav Ghosh
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0

You can not pass more than two argument in main function. In main function, you can pass only two argument or Zero argument.

Using following parameters, you can pass the value command line. 

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