Question

I’m working on building my own string class and I’m having some trouble with substring

// Substring operator
// reutns a substring from a given point
String String::Substring(int startPosition, int length) const{
    if(length==0)
        length = GetLength()+1; //Takes care of null terminator, im not worried about if length is imputed yet
    char* result = new char[length-startPosition]; // Assume it's not negative for the sake of just getting it to work, It would only be negative if it's user error
    for(int i=startPosition; i<length; i++)
        result[i] = Text[i]; //Since it will always  go from a given point to the end, the null terminator will transfer in the for loop.

    return result;
}

Text is the data member for the string class. I get a unhandled exception, Access violation reading location.

While I was debugging it was going through these processes

// Init-constructor for initializing this string with a C-string
String::String(const char* text){
    *this = text;
}

and

// Assigns C-string to this String
String& String::operator = (const char* text){
    // Delete the existing string first
    delete[] Text;

    // +1 accounts for null terminator
    int trueLength = GetLength(text)+1;

    // Allocate new memory
    Text = new char[trueLength];

    // Copy all characters from source into Text
    for ( int i = 0; i < trueLength; i++)
        Text[i] = text[i];

    return *this;
}

I can’t figure out what I’m doing wrong, thanks for your help.

Answer 1

Consider what happens when you create a String object using the char* constructor:

String::String(const char* text){
  *this = text;
}

None of the members are initialized yet, and you invoke operator=:

String& String::operator = (const char* text){
  // Delete the existing string first
  delete[] Text;

You delete member Text, even though you have not yet initialized it. Deleting an unitialized pointer yields undefined behavior. In this case, the behavior is an exception.

Either initialize Text to null in your constructor before invoking operator=, or do all of the work in your constructor, not your assignment operator.