Sending a string variable as a parameter to open a file

Question

In main:

void HandleAction(const RandomWriter & rw, string choice)
{
   if(choice == "P")
   {
     string fileInput;
     cout << "Change input file: " << endl;
     cin >> fileInput;
     rw.SetFilename(fileInput);
   }
}

In a RandomWriter class:

void RandomWriter::SetFilename(string filename)
{
 string text = GetFullFile(filename);
 if (text != "")
{
  fullText = text;
  this->filename = filename;
}

/

Why am i getting this error when i try to pass fileInput as a parameter to SetFileName?

Thanks in advance guys!

||=== error: passing 'const RandomWriter' as 'this' argument of 'void RandomWriter::SetFilename(std::string)' discards qualifiers [-fpermissive]|

Read trough the answers here stackoverflow.com/questions/2382834/discards-qualifiers-error — Nayana Adassuriya
– Nayana Adassuriya, Commented May 11, 2016 at 3:16
If you want to check if a std::string object is empty or not, there's the empty member function. — Some programmer dude
– Some programmer dude, Commented May 11, 2016 at 3:18

Some programmer dude · Accepted Answer · 2016-05-11 03:14:46Z

1

In the HandleAction function you say that the rw is a reference to a constant RandomWriter object. Then you try to call a member function on the rw object that tries to modify the constant object. That is of course not allowed, you can't modify constant objects.

So the simple solution is to remove the const part of the argument specification:

void HandleAction(RandomWriter & rw, string choice) { ... }
//                ^^^^^^^^^^^^^^^^^
//         Note: No longer constant

On a related note, you should probably use references to constant objects for the strings though, no need to copy them all the time.

answered May 11, 2016 at 3:14

Some programmer dude

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Comments

Ryan Palmer · Accepted Answer · 2016-05-11 03:20:04Z

0

Your RandomWriter parameter rw is declared const in your HandleAction() method, and is thus immutable and unable to be changed by your call to SetFilename().

answered May 11, 2016 at 3:20

Ryan Palmer

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