Segmentation Fault with Dynamic Class (homework problem) - c++

Question

I'm attempting to convert a working static String class to a dynamic String class using pointers, but when I implement the pointer it throws a segmentation fault error. Code below:
mystring1.h:
//File: mystring1.h
// Declaration file for user-defined String class.
#ifndef _MYSTRING_H
#define _MYSTRING_H
#include<iostream>
#include <cstring>
using namespace std;
#define MAX_STR_LENGTH 200
class String {
public:
String();
String(const char *s); // a conversion constructor
void append(const String &str);
//deconstructor
~String();
//copy constructor
String (const String & origString);
//assignment operator overload
String operator =(const String &origString);
// Relational operators
bool operator >(const String &str) const;
bool operator <(const String &str) const;
String operator +=(const String &str);
void print(ostream &out) const;
int length() const;
char operator [](int i) const; // subscript operator
private:
char *contents;
int len;
//int capacity;
};
ostream & operator<<(ostream &out, const String & r); // overload ostream operator "<<" - External!
#endif /* not defined _MYSTRING_H */
mystring1.cpp:
//File: mystring1.h
// Implementation file for user-defined String class.
#include "mystring1.h"
String::String()
{
contents[0] = '\0';
len = 0;
}
String::String(const char s[])
{
len = strlen(s);
contents = new char[len + 1];
strcpy(contents, s);
}
void String::append(const String &str)
{
strcat(contents, str.contents);
len += str.len;
}
//deconstructor
String::~String()
{
delete [] contents;
}
//copy constructor
String::String(const String &origString)
{
len = origString.len;
contents = new char[len + 1];
for (int i = 0; i < len; i++)
{
contents[i] = origString.contents[i];
}
}
//assignment operator overload
String String::operator =(const String &origString)
{
if (this != &origString)
{
len = origString.len;
delete [] contents;
contents = new char[len + 1];
for (int i = 0; i < len; i++)
{
contents[i] = origString.contents[i];
}
}
return *this;
}
bool String::operator >(const String &str) const
{
return strcmp(contents, str.contents) > 0;
}
bool String::operator <(const String &str) const
{
return strcmp(contents, str.contents) < 0;
}
String String::operator +=(const String &str)
{
append(str);
return *this;
}
void String::print(ostream &out) const
{
out << contents;
}
int String::length() const
{
return len;
}
char String::operator [](int i) const
{
if (i < 0 || i >= len) {
cerr << "can't access location " << i
<< " of string \"" << contents << "\"" << endl;
return '\0';
}
return contents[i];
}
ostream & operator<<(ostream &out, const String & s) // overload ostream operator "<<" - External!
{
s.print(out);
return out;
}
Assignment 5 Driver:
/**
* cmpsc122 Assignment 5 test file
* File Name: Assign5driver.cpp
*
* Description: This program demonstrates a basic String class that implements
* dynamic allocation and operator overloading.
*
*/
#include <iostream>
#include "mystring1.h"
using namespace std;
/*************************** Main Program **************************/
int main()
{
String str1, str2("dog"); // Using constructor for initial strings
char s1[100], s2[100]; // Some C strings.
// Print out initial strings
cout << "Initial values:" << endl;
cout << "str1 holds \"" << str1 << "\" (length = " << str1.length() << ")" << endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
// Inputs some new strings in them
cout << "\nEnter a value for str1 (no spaces): ";
cin >> s1;
str1 = s1;
cout << "\nEnter a value for str2 (no spaces): ";
cin >> s2;
str2 = s2;
cout << "\nAfter assignments..." << endl;
cout << "str1 holds \"" << str1 << "\" (length = " << str1.length() << ")" << endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
// Get some elements...
int i;
cout << "\nEnter which element of str1 to display: ";
cin >> i;
cout << "Element #" << i << " of str1 is '" << str1[i] << "'" << endl;
cout << "\nEnter which element of str2 to display: ";
cin >> i;
cout << "Element #" << i << " of str2 is '" << str2[i] << "'" << endl;
// Concate some strings
cout << "\nEnter a value to append to str1 (no spaces): ";
cin >> s1;
// str1.append(s1); // Actually, the cstring is converted to String object here by the constructor
str1 += s1; // same as above
cout << "\nEnter a value to append to str2 (no spaces): ";
cin >> s2;
str2 += s2;
cout << "\nAfter appending..." << endl;
cout << "str1 holds \"" << str1 << "\" (length = " << str1.length() << ")" << endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
// Compare strings...
cout << "\nComparing str1 and str2..." << endl;
cout << "\"";
cout<< str1; // test the overloading of ostream operator <<
cout << "\" is ";
if (str1 < str2) { // test the overloading of comparison operator <
cout << "less than";
} else if (str1 > str2) {
cout << "greater than";
} else {
cout << "equal to";
}
cout << " \"";
cout << str2;
cout << "\"" << endl;
cout << "\ntest the = operator, after str1 = str2; "<< endl;
str1 = str2;
cout << "str1 holds \"" << str1 << "\" (length = " << str1.length() << ")" << endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
str1 += s1;
cout << "\nAfter str1 = str1 + s1: "<< endl;
cout << "str1 holds \"" << str1 << "\" (length = " << str1.length() << ")" << endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
String str3(str2);
cout << "\ntest the copy constructor, after str4(str3);"<< endl;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
cout << "str3 holds \"" << str3 << "\" (length = " << str3.length() << ")" << endl;
cout << "\nafter appending str2 by str1" << endl;
str2 += str1;
cout << "str2 holds \"" << str2 << "\" (length = " << str2.length() << ")" << endl;
cout << "str3 holds \"" << str3 << "\" (length = " << str3.length() << ")" << endl;
cout<< "\nstr3 are not changed. Type any letter to quit." << endl;
char q;
cin >> q;
return 0;
}
Any help would be appreciated, I have tried all that I can and my research into segmentation fault causes isn't doing much to help.

Answer 1

There are several immediately obvious bugs in your implementation:
The default constructor uses uninitialized contents pointer.
The ::append() method does not ensure there is sufficient space in the destination buffer before performing strcat.
The copy constructor and the ::operator=() method do not NUL-terminate the contents buffer.
There are likely more.
You should build your test program with g++ -fsanitize=address ... and fix all the bugs it finds.
You should also build your program with -Wall -Wextra flags, and fix all the warning it produces.