CODEWITHSUNDEEP
c++buildertstringlist
Jacek
Jacek

Reputation: 63

How to change a Char in a String in a TStringList

After writing the content of the text file to the TStringList object, I try to change one character in the line and then write the entire content of the object back to the file. In the saved file, the changed line character was not saved as expected and is still unchanged. To write the change of character to the file I need to use the String object.

void __fastcall TForm1::Button1Click(TObject *Sender)
{
 TStringList *Lista = new TStringList;

 if(OpenDialog1->Execute())
    Lista->LoadFromFile(OpenDialog1->FileName);

   Lista->Strings[0][1] = '0'; // this does not work 

  // Only this way work 
  String A = Lista->Strings[0];
  A[1] = '0';
  Lista->Strings[0] = A;
}

I don't understand why the sign change directly in the TStringList object doesn't happen, or if it does, why isn't it written to the file.

Upvotes: 0

Views: 87

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 596437

The TStringList::Strings[] property getter DOES NOT return a reference to a String object, like you are expecting. It returns a String object by value instead, which means a copy is returned as a temporary object.

Strings[0][1] = ... has no effect because you are modifying that temporary object and not assigning it anywhere afterwards, so it just goes out of scope immediately.

That is why you need to save that temporary object to a local variable first, and then assign that variable back to the Strings[] property after modifying the variable's data.

Upvotes: 2

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