MFC Edit Control: How to replace a line in a multi-line edit control?

Q: How to replace a line in a multi-line edit control?

A: The example below shows how it can be done and to avoid often made mistakes.

Code:

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void CMyDialog::ReplaceEditLineText(int nLine, LPCTSTR pszNewText)
{
  // 'CEdit::LineIndex()' takes as parameter the index of the line
  // and returns the character index of the line specified.

  // The character index is is the number of characters from
  // the beginning of the edit control to the specified line.

  const int nLineStart = m_edit.LineIndex(nLine);

  if(nLineStart != -1)
  { 
    // 'CEdit::LineLength()' takes as parameter the character index
    // of the line and not the line index as often is mistaken.

    const int nLineLength = m_edit.LineLength(nLineStart);

    // select the line, and replace the text.

    m_edit.SetSel(nLineStart, nLineStart + nLineLength);
    m_edit.ReplaceSel(pszNewText);
  }
}

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