I have homework that I need to make a custom string class using C type strings. Most of it seems okay but I am getting a runtime error as soon as I test it and it isn’t performing all my tests like it should. Specifically my += operator seems to have something wrong with it but I can’t understand what.
I can’t add in or change any of the prototypes and I should use C++ constructs over C type where possible.
Thanks!
#include <iostream>
#include <string>
#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') {
++i;
}
strSize = i;
strPtr = new char [i+1];
for (i=0; i < strSize; ++i) {
strPtr[i] = str[i];
}
}
//Copy constructor
TStr::TStr(const TStr& str) {
strPtr = new char[str.strSize];
strcpy(strPtr, str.strPtr);
}
//Destructor
TStr::~TStr() {
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) {
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;
}
//overload two relational operators as member functions
bool TStr::operator == (const TStr& str) const {
int value = strcmp(strPtr, str.strPtr);
if (value == 0) {
return true;
} else {
return false;
}
/*int counter=0;
for (int i=0; i < strSize; ++i) {
if (strPtr[i] == str.strPtr[i]) {
++counter;
}
}
if (counter == strSize) {
return true;
} else {
return false;
}
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;
}
//Overload the stream insertion and extraction operators.
ostream& operator << (ostream& out, const TStr& str) {
int size = str.strSize;
for (int i=0; i < size; ++i) {
out << str[i];
}
return out;
}
istream& operator >> (istream& in, TStr& str) {
return in;
}
//overload two other relational operators as global functions
bool operator != (const TStr& S1, const TStr& S2) {
return !(S1 == S2);
}
bool operator <= (const TStr& S1, const TStr& S2) {
return (S1 < S2 || S1 == S2);
}
bool operator > (const TStr& S1, const TStr& S2) {
return !(S1 < S2);
}
bool operator >= (const TStr& S1, const TStr& S2) {
return !(S1 < S2 || S1 == S2);
}
//overload the concatenation operator as a global function
TStr operator + (const TStr& str1, const TStr& str2) {
//return (str1 += str2);
//return (str1 + str2);
}
This is what I’m testing with:
int main() {
authors();
TStr str1 = "VENI"; //initialize str1 using
//the assignment operator
const TStr str2("VEDI"); //initialize str2 using the
//conversion constructor
TStr str3; //initialize str3 to null
TStr str4; //initialize str4 to null
cout << "\nTest 1: str1: " << str1 << " str2 " << str2
<< " str3 " << str3 << " ###.\n" ; //Test 1
if (str1 <= str2) //Test 2
cout << "\nTest 2: " << str1 << " is less "
<< "than " << str2 << endl;
else
cout << "\nTest 2: " << str2 << " is less "
<< "than " << str1 << endl;
str1=" Pride is what we have.";
str3 = str1; //Test 3
cout << "\nTest 3: The new value of str3 = "
<< str3 << endl;
str3 += " Vanity is what others have. ";
cout<<"\nTest 4: The str3: '" << str3<<"' \nhas "; //test 4
cout<< countVowels(str3)<<" vowels "<< endl;
/*TStr str5 = str1 + str2 + str3;
cout<<"\nTest 5: The str5: '" << str5<<"' \nhas "; //test 5
cout<<countVowels(str5)<<" vowels \n";
cout<<"\nTest 6: The str3 again: " << str3 <<endl; //test 6
cout<<"\n\n Bye, Bye!";*/
return 0;
}
EDIT: I should have added that I need to get the tests to work as part of the homework.
EDIT 2: Here are the functions I changed so far.
//constructor; conversion from the char string
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];
strPtr[i + 1] = '\0'; //<- this
}
}
//Copy constructor
TStr::TStr(const TStr& str) {
strPtr = new char[str.strSize + 1]; //<-this
strcpy(strPtr, str.strPtr);
}
//overload the concatenation oprerator
TStr TStr::operator += (const TStr& str) {
char *buffer = new char[strSize + str.strSize + 1]; //<- this
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 + 1]; //<- this
assert(strPtr);
for (int i=0; i<strSize; ++i) {
strPtr[i] = str.strPtr[i];
}
}
return *this;
}
EDIT 3: Unfortunately changing it to below did nothing really. It might be the = operator that’s causing the problem as it now fails just after test 3.
//constructor; conversion from the char string
TStr::TStr(const char *str) {
int i=0;
while (str[i] != '\0') {
++i;
}
strSize = i;
strPtr = new char [i+1];
strcpy(strPtr, str);
}
You have several problems involving the null-terminator with several of your functions(some of these you have fixed in your edits, but I’m just going to cover them all anyway, so that this is a thorough answer).
In the constructor converting from(fixed)const char *, you are not copying over the null-terminator to strPtr.In your copy constructor, you are not allocating enough room for the null-terminator.(fixed)In your assignment operator, you are not allocating enough room for the null-terminator.(fixed … not exactly, see #5)