Re: C++ Primer ex 7.16 - arguments to main

From:
"Victor Bazarov" <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Thu, 16 Aug 2007 10:47:28 -0400
Message-ID:
<fa1o1u$6go$1@news.datemas.de>
arnuld wrote:

On Thu, 16 Aug 2007 12:58:31 +0000, Erik Wikstr?m wrote:

I usually write this as

   int main (int argc, char* argv[])

That is, argv is an array of pointers to char, or argv is an array of
pointers to NULL-terminated C-strings, where each string is an
argument passed to the program, and argc is the number of elements
in the array. In fact argc is short for "argument count" and argv is
"argument values".

This reduces the problem to a loop over an array and printing
C-strings.


ok, here it is in 2 versions, one with indexing and one with pointers,
both fall under an infinite-loop :(

#include <iostream>

int main( int argc, char *argv[] )
{
 std::cout << "These arguments were passed to 'main()'" << std::endl;

 /* an int value can be printed easily */ std::cout << argc <<
std::endl;

 int i = 0;

 while( i < argc )
   {
     std::cout << argv[i] << "\n";


Are you hoping the compiler will increment 'i' for you?

   }

 return 0;
}

------- pointer version ------------------- #include <iostream>

int main( int argc, char *argv[] )
{
 std::cout << "These arguments were passed to 'main()'" << std::endl;

 /* an int value can be printed easily */
 std::cout << argc << std::endl;

 char *pchar = argv[0];

 while( *pchar != '\0' )
   {
     std::cout << *pchar << "\n";


Even if you increment 'pchar' here (which is needed, of course,
because the compiler cannot figure out what you want it to do
unless you actually tell it), you will just print out all the
characters of the first argument to your program, one character
on each line. All other arguments will be left out.

   }

 return 0;
}


Here is the solution with pointers:

    while (*argv)
        std::cout << *argv++ << std::endl;

And if you need to keep the value of 'argv' intact, copy it into
another pointer to pointer to char:

    char **pstr = argv;
    while (*pstr)
        std::cout << *pstr++ << std::endl;

V
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