Crash on string::insert?

[Exiled]

Alright. I'm currently making a login screen for my game. I'm using the library of Allegro 4.2.3. I'm making some textboxes(for the username + password), and receiving input from them with the following function.

#include <string>
using namespace std;
#include <allegro.h>
#include "textbox.h"

void TextboxInput(Textbox&t, int&caret, string::iterator&iter, bool&insert) {
     string edittext = t.txt;
     
     while(keypressed()) {
          int  newkey   = readkey();
          char ASCII    = newkey & 0xff;
          char scancode = newkey >> 8;

          // a character key was pressed; add it to the string
          if(ASCII >= 32 && ASCII <= 126) {
               // add the new char, inserting or replacing as need be
               if(insert || iter == edittext.end())
                    iter = edittext.insert(iter, ASCII);
               else
                    edittext.replace(caret, 1, 1, ASCII);

               // increment both the caret and the iterator
               caret++;
               iter++;
          }
          // some other, "special" key was pressed; handle it here
          else
               switch(scancode) {
                    case KEY_DEL:
                         if(iter != edittext.end()) iter = edittext.erase(iter);
                         break;

                    case KEY_BACKSPACE:
                         if(iter != edittext.begin()) {
                              caret--;
                              iter--;
                              iter = edittext.erase(iter);
                         }
                         break;
            
                    case KEY_RIGHT:
                         if(iter != edittext.end()) caret++, iter++;
                         break;
            
                    case KEY_LEFT:
                         if(iter != edittext.begin()) caret--, iter--;
                         break;
            
                    case KEY_INSERT:
                         insert = !insert;
                         break;

                    default:
                         break;
               }
         } 
      
      t.txt = edittext; 
}

The function above is basically consisting of some copy + pasted code from a tutorial I found. I'm using the exact code from it. Strangely enough, I've used the same exact code in the past; it worked fine. Now, I receive a program crash at the line: iter = edittext.insert(iter, ASCII); after I have typed one character into the string. I have no idea why it's happening. Any help would be appreciated. If you need more details, please let me know - I know I'm bad at explaining things, heh.

Well, thanks for reading!

[Bootstrapper]

Huh, now that looks like an invalid iterator. Try to check that one, probably at the function-call...

[Exiled]

Thanks for the reply! I can see why the iterator would have something to do with it, for only string.insert() and string.erase() crash the program, while replace() works fine. How exactly would I fix this? I'm not familiar with string iterators as much as I should be, and I'm pretty clueless about what makes an iterator valid or not.

Thanks for the help!

[Exiled]

Bump :/

[Bootstrapper]

Well, what iterator do you overgive at the function call?

[Exiled]

I use the one that is defined like the following:

string::iterator iter = username.txt.begin();