Thread: Order of Operations Question

Originally Posted by The Brain

I would just like to see an example of a "literal string" where using 'system ( )' is acceptable to the general programming community.

Well, because a string literal is converted to a pointer when passed to a function, your request presumably allows pointers, so the only 100% portable usage of system is:

Code:

int has_command_processor = std::system(0);

Everything else is implementation-defined.

You were trying for something like this?

Code:

#include <cstdlib>
#include <cstring>  // For strcpy
#include <iostream>

using namespace std;

int main()
{
  char line[80];
  char para[5][80];
  int  it;

  // Get the lines of a paragraph
  // Terminate at N lines or end-of-file
  for (it = 0; it < 5; it++) {
    if (!cin.getline(line, sizeof line)) {
      break;
    }
    strcpy(para[it], line);
  }
  // Check for fatal errors
  if (it < 5 && !cin.eof()) {
    cerr<<"Something really bad happened!"<<endl;
    return EXIT_FAILURE;
  }
  // Display the final paragraph
  cout<<"The paragraph is: "<<endl;
  for (int j = 0; j < it; j++) {
    cout<< para[j] <<endl;
  }

  return EXIT_SUCCESS;
}

Note how strcpy is used to transfer the contents of the arrays. This is because (as you probably know) arrays can't be assigned with the assignment operator. para is declared to be an array of 5 arrays of 80 characters. The first dimension designates lines and the second dimension represents characters in a line. Also notice that the loop condition checks for array overflow while a conditional inside the loop breaks if getline fails. After the loop the code checks to see if getline failed due to end-of-file (as we want). If something else made it fail then we print an error because there's really not much else to do in such a simple program. Error checking is important, especially when using input status codes that could be informative or erroneous. The last loop uses i as the upper limit because the array might not have been filled up.

I couldn't help but notice that you're using old-style C++. Life would be much easier for you if you migrated to a modern compiler that would properly support standard niceties. Then you could do this and not worry about lengths:

Code:

#include <cstdlib>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
  typedef vector<string> paragraph;
  string    line;
  paragraph para;

  // Get the lines of a paragraph
  // Terminate at end-of-file
  while (getline(cin, line)) {
    para.push_back(line);
  }
  // Check for fatal errors
  if (!cin.eof()) {
    cerr<<"Something really bad happened!"<<endl;
    return EXIT_FAILURE;
  }
  // Display the final paragraph
  cout<<"The paragraph is: "<<endl;
  paragraph::const_iterator it = para.begin();
  while (it != para.end()) {
    cout<< *it <<endl;
    ++it;
  }

  return EXIT_SUCCESS;
}

This is much safer. It lets you create paragraphs of arbitrary length with minimal effort (less than the constrained version above!). The functionality is the same: Lines are read until end-of-file, no arbitrary line limit or limit on the number of lines you'll see, the status of cin is checked as before, and the each line is printed out. I used iterators instead of indices for the printing simply because it's more modern. In this case, the following loop would do the same thing:

Code:

for (paragraph::size_type it = 0; it < para.size(); it++) {
  cout<< para[it] <<endl;
}

It's generally better to get into the habit of using iterators though. They're very flexible and you'll be happy you got used to them when you start powerusing the standard library.

Oh SALEM! Where are you, Salem?

>...now to throw in the whole "the standards say you can leave return 0 out of main" argument...
But they don't say you must leave it out.

>Oh SALEM! Where are you, Salem?

Major_small is referring to a common argument that gets sparked on this board about int main() vs void main(). A brief look at Salem's avatar will show you what I'm talking about.

Originally Posted by sean_mackrory

Major_small is referring to a common argument that gets sparked on this board about int main() vs void main(). A brief look at Salem's avatar will show you what I'm talking about.

I'm familiar with Salem's avatar, and the "void main gestapo" , but the reference is somewhat confusing as the discussion hasn't quite yet gone off on that tangent (though it wouldn't surprise me if it did).

It just did

Since when is using system(); a security issue? Yes, people could write their own 'pause' command and put a virus in it, but would they really want to considering its running on their own computer?

It makes it easier to attach spyware