Regarding main int argc char argv

Question

Possible Duplicates    What are the arguments to main   for    What does int argc  char  argv   mean        Every program is starting with the main int argc  char  argv    definition    I don t understand what it means  I would be very glad if somebody could explain why we use these arguments if we don t use them in the program  Why not just  int main     Is the name of the program one of the elements of  argv   and argc is the count of the number of arguments in  argv    What are the other arguments sent to  argv    How do we send them

User · Answer

Those are for passing arguments to your program, for example from command line, when a program is invoked

$ gcc mysort.c -o mysort

$ mysort 2 8 9 1 4 5

Above, the program mysort is executed with some command line parameters. Inside main( int argc, char * argv[]), this would result in

Argument Count, argc = 7

since there are 7 arguments (counting the program), and

Argument Vector, argv[] = { "mysort", "2", "8", "9", "1", "4", "5" };

Following is a complete example.

$ cat mysort.c
#include <stdio.h>
int main( int argc, char * argv [] ) {
    printf( "argc = %d\n", argc );
    for( int i = 0; i < argc; ++i ) {
        printf( "argv[ %d ] = %s\n", i, argv[ i ] );
    }
}

$ gcc mysort.c -o mysort

$ ./mysort 2 8 9 1 4 5
argc = 7
argv[ 0 ] = ./mysort
argv[ 1 ] = 2
argv[ 2 ] = 8
argv[ 3 ] = 9
argv[ 4 ] = 1
argv[ 5 ] = 4
argv[ 6 ] = 5

[The char strings "2", "8" etc. can be converted to number using some character to number conversion function, e.g. atol() (link)]

User · Answer

You can run your application with parameters such as app -something -somethingelse  int argc represents number of these parameters and char  argv   is an array with actual parameters being passed into your application  This way you can work with them inside of your application

User · Answer

argc is the number of command line arguments given to the program at runtime  and argv is an array of arrays of characters  rather  an array of C-strings  containing these arguments  If you know you re not going to need the command line arguments  you can declare your main at taking a void argument  instead   int main void                       Those are the only two prototypes defined for main as per the standards  but some compilers allow a return type of void as well  More on this on Wikipedia

User · Answer

The comp lang c FAQ deals with the question  What s the correct declaration of main     in Question 11 12a

User · Answer

With argc  argument count  and argv  argument vector  you can get the number and the values of passed arguments when your application has been launched   This way you can use parameters  such as -version  when your application is started to act a different way   But you can also use int main void  as a prototype in C   There is a third  less known and nonstandard  prototype with a third argument which is envp  It contains environment variables     Resources    Wikipedia - Main function  C and C

User · Answer

argc means the number of argument that are passed to the program  char  argv   are the passed arguments  argv 0  is always the program name itself  I m not a 100  sure  but I think int main   is valid in C C

User · Answer

The arguments argc and argv of main is used as a way to send arguments to a program  the possibly most familiar way is to use the good ol  terminal where an user could type cat file  Here the word cat is a program that takes a file and outputs it to standard output  stdout    The program receives the number of arguments in argc and the vector of arguments in argv  in the above the argument count would be two  The program name counts as the first argument  and the argument vector would contain  cat file null   While the last element being a null-pointer   Commonly  you would write it like this   int     Specifies that type of variable the function returns          main   must return an integer main   int argc  char   argv             code      return 0     Indicates that everything went well      If your program does not require any arguments  it is equally valid to write a main-function in the following fashion   int main          code   return 0     Zero indicates success  while any       Non-Zero value indicates a failure error     In the early versions of the C language  there was no int before main as this was implied  Today  this is considered to be an error   On POSIX-compliant systems  and Windows   there exists the possibility to use a third parameter char   envp which contains a vector of the programs environment  variables  Further variations of the argument list of the main function exists  but I will not detail it here since it is non-standard   Also  the naming of the variables is a convention and has no actual meaning  It is always a good idea to adhere to this so that you do not confuse others  but it would be equally valid to define main as  int main int c  char   v  char   e          code    return 0      And for your second question  there are several ways to send arguments to a program  I would recommend you to look at the exec   family of functions which is POSIX-standard  but it is probably easier to just use system  command arg1 arg2    but the use of system   is usually frowned upon as it is not guaranteed to work on every system  I have not tested it myself  but if there is no bash zsh  or other shell installed on a  NIX-system  system   will fail

User · Answer

argc is the number of command line arguments and argv is array of strings representing command line arguments   This gives you the option to react to the arguments passed to the program  If you are expecting none  you might as well use int main

[c] Regarding 'main(int argc, char *argv[])'

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