Question

I have an assignment that I need to create a custom C type string class in C++. I am having trouble getting this to work. Currently my code crashes with a run time error right at the start. I also know many of my function are wrong but I want to get the member functions sorted before I go on and fix the other functions. Bear in mind that all the function prototypes were given to us and I can not change them. I need to write the ‘guts’ so to speak.

What is wrong with my constructor for a start?

#include <iostream>
#include "tstr.h"
using namespace std;

//Default constructor to initialize the string to null
TStr::TStr() {
    strPtr = 0;
    strSize = 0;
}  
//constructor; conversion from the char string
TStr::TStr(const char *str) {
    int i=0;
    while (str[i] != '/0') {
        strPtr = new char [strlen(str)+1];
        for (i=0; i <strSize;++i) {
            strPtr[i] = str[i];
        }
        ++i;
    }
    strSize = i;
} 
//Copy constructor
TStr::TStr(const TStr&) {
}
//Destructor
TStr::~TStr() {
    if (strPtr) {
        delete[] strPtr;
    }
}

//subscript operators-checks for range
char& TStr::operator [] (int i) {
    assert (i >= 0 && i < strSize);
    return strPtr[i];
}
const char& TStr::operator [] (int i) const {
    assert (i >= 0 && i < strSize);
    return strPtr[i];
}

//overload the concatenation oprerator
TStr TStr::operator += (const TStr& str) {
    //this->strPtr += str.strPtr;
    //this->strSize += str.strSize;
    return *this;
}
//overload the assignment operator
const TStr& TStr::operator = (const TStr& str) {
    if (this != &str) {
        delete[] strPtr;
        strPtr = new char[strSize = str.strSize];
        assert(strPtr);
        for (int i=0; i<strSize; ++i) {
            strPtr[i] = str.strPtr[i];
        }
    }
    return *this;
}

//overload two relational operators as member functions
bool TStr::operator == (const TStr& str) const {
    return (strPtr == str.strPtr && strSize == str.strSize);
}
bool TStr::operator < (const TStr& str) const {
    return (strPtr < str.strPtr && strSize < str.strSize);
}
//the length of the string
int TStr::size() {
    return strSize;
}

Thanks for any replies/help! 🙂

EDIT 1: Okay the constructor is now working but I am still getting a runtime error and I’m 90% sure it is to do with my overloaded += operator. It looks fine though and compiles okay. What am I missing?

(Note: Only small changes have been made to the above code, but let me know if you want to see the whole lot.)

//overload the concatenation oprerator
TStr TStr::operator += (const TStr& str) {
    for(int i = 0; i < strSize; ++i) {
        strPtr[i] += str.strPtr[i];
    }
    return *this;
}

EDIT 2: Okay this what I have now. Compiles fine but doesn’t actually add the two strings together with the += like it should. Anyone got any ideas?

//overload the concatenation oprerator
TStr TStr::operator += (const TStr& str) {
    char *buffer = new char[strSize + str.strSize + 1];
    strcpy(buffer, strPtr);
    strcat(buffer, str.strPtr);
    delete [] strPtr;
    strPtr = buffer;
    return *this;
}

//overload the assignment operator
const TStr& TStr::operator = (const TStr& str) {
    if (this != &str) {
        delete[] strPtr;
        strPtr = new char[strSize = str.strSize];
        assert(strPtr);
        for (int i=0; i<strSize; ++i) {
            strPtr[i] = str.strPtr[i];
        }
    }
    return *this;
}

Answer 1

Your ctor is pretty much a mess.

You use i for two different things — at the same time. You also copy the entire contents of str into strPtr once for each character in str.

Basically, you have to decide, are you going to use the C run-time library or not?

Using it:

TStr::TStr(const char *str) 
{
  strSize = strlen(str);
  strPtr = new char [strSize+1];
  strcpy(strPtr, str);
}

not using it:

TStr::TStr(const char *str) 
{
  int i = 0;
  while (str[i] != '\0') 
       ++i;
  strSize = i;
  strPtr = new char [i+1];
  for (i=0; i < strSize;++i)
        strPtr[i] = str[i];
}