now what?

**Luigi** · 05-10-2003

why do I get an error for that?

Code:

istream* input;

int main(int argc, char* argv[])
{
      switch (argc)
      {
	  case 1:		// read from standard input
	        input = &cin;
	        break;
	  case 2:
	        input = new istringstream(argv[1]);		// read argument string
	        break;
	  default :
	        error ("Too many arguments");
	        return 1;
      }

...

I get the following error :

Error : illegal use of incomplete struct/union/class 'std::basic_istringstream<char, std::char_traits<char>, std::allocator<char>>'
calc.cpp line 94 input = new istringstream(argv[1]); // read argument string

**gustavosserra** · 05-10-2003

My compiler doesn´t accept your code, so I´m trying to explain with a different example. Istringstream is a template:

'std::basic_istringstream<char, std::char_traits<char>, std::allocator<char>>'

and templates have different new usage. Like this:

Code:

list<int> *vet;

int main(int argc, char* argv[])
{
  //vet  = new list;  this is wrong
  vet = new list<int>();

}

Hope that helps... what compiler do you use anyway?

**confuted** · 05-10-2003

Check out his signature :P

**PorkyChop** · 05-11-2003

It works on my compiler(gcc 3.2)...

**PorkyChop** · 05-11-2003

Also, though not obvious, there is kind of a logic flaw with that code. In the first case, input is assiged to cin's memory address. In the second case, you assign it to a newly allocated istringstream. As you know, you will have a memory leak if you don't delete that istringstream object. However, after the switch statement, how will you know if you assigned input to cin or to a new istringstream? If you try to delete input when it is assigned to cin, you will get a big fat error(or at least I do on my OS). Also, wouldn't you be able to accomplish the same thing like this:

Code:

#include <iostream>
#include <string>

using namespace std;

int main(int argc, char** argv) {

	string argvar;

	switch(argc) {

	case 1: cin >>argvar; 		break;
	case 2: argvar = argv[1]; 	break;

	default: cerr <<"Too many arguments!\n"; return 0;
	}

	//Now you have your argument in argvar
}

Hope that helps.

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