MyString Class

[Luis]

Below is my project. My Code is done, but when I try to compile it, my IDE
crahses (again). I fixed up all the things you guys said I should, except
for some which would not meet the project requiremnts. here is my code. it
compiles, but crashes winsioux.

#ifndef MYSTRING_H
#define MYSTRING_H


#include <iostream>
using namespace std;

class MyString {
public:
//Constructors, Copy, and Destrctors

MyString(); //one of four
MyString(const char *inString); //two of four
MyString operator=(const MyString right); //three of four
MyString(const MyString &right); //four of four
~MyString(); //destructor

//input/output
int length()const;
friend ostream& operator<<(ostream& out,const MyString &outString);
friend istream& operator>>(istream& in,MyString &inString);
void read(istream& inString,char delimit);
//Overloaded brackets
char& operator[](int index);
char operator[](int index)const;

friend MyString operator+(const MyString left,const MyString right);
MyString& operator+=( const MyString &right);

friend bool operator<(const MyString &left, const MyString &right);
friend bool operator<=(const MyString &left, const MyString &right);
friend bool operator>=(const MyString &left, const MyString &right);
friend bool operator>(const MyString &left, const MyString &right);
friend bool operator==(const MyString &left, const MyString &right);
friend bool operator!=(const MyString &left, const MyString &right);
private:
char * string;

};

#endif



/*
* -------------------
* These functions are designed to help you test your MyString objects,
* as well as show the client usage of the class.
*
* The BasicTest function builds an array of strings using various
* constructor options and prints them out. It also uses the String
* stream operations to read some strings from a data file.
*
* The RelationTest function checks out the basic relational operations
* (==, !=, <, etc) on Strings and char *s.
*
* The ConcatTest functions checks the overloaded + and += operators that
* do string concatenation.
*
* The CopyTest tries out the copy constructor and assignment operators
* to make sure they do a true deep copy.
*
* Although not exhaustive, these tests will help you to exercise the basic
* functionality of the class and show you how a client might use it.
*
* While you are developing your MyString class, you might find it
* easier to comment out functions you are ready for, so that you don't
* get lots of compile/link complaints.
*/

#include "mystring.h"
#include <fstream>
#include <cctype> // for toupper()
#include <string> // for strchr(), strstr(), etc.
#include <cassert>
#include <iostream>
using namespace std;

bool eof(istream& in);
void BasicTest();
void RelationTest();
void ConcatTest();
void CopyTest();
MyString AppendTest(const MyString& ref, MyString val);

int main()
{
BasicTest();
RelationTest();
ConcatTest();
CopyTest();

}



bool eof(istream& in)
{
char ch;
in >> ch;
in.putback(ch);
return !in;
}


void BasicTest()
{
cout << "----- Testing basic String creation & printing" << endl;

const MyString strs[] =
{MyString("Wow"), MyString("C++ is neat!"),
MyString(""), MyString("a-z")};


for (int i = 0; i < 4; i++){
cout << "string [" << i <<"] = " << strs << endl;
}



cout << endl << "----- Now reading MyStrings from file" << endl;


cout << endl << "----- first, word by word" << endl;
ifstream in("string.data");
assert(in);
while (!eof(in)) {
MyString s; // creates an empty string
if (in.peek() == '#') { // peek at char, comments start with #
in.ignore(128, '\n'); // skip this line, it's a comment
} else {
in >> s;
cout << "Read string = " << s << endl;
}
}
in.close();

cout << endl << "----- now, line by line" << endl;
ifstream in2("string.data");
assert(in2);
while (!eof(in2)) {
MyString s; // creates an empty string
if (in2.peek() == '#') { // peek at char, comments start with #
in2.ignore(128, '\n'); // skip this line, it's a comment
} else {
s.read(in2, '\n');
cout << "Read string = " << s << endl;
}
}
in2.close();



cout << endl << "----- Testing access to characters (using const)" <<
endl;
const MyString s("abcdefghijklmnopqsrtuvwxyz");
cout << "Whole string is " << s << endl;
cout << "now char by char: ";
for (int i = 0; i < s.length(); i++){
cout << s;
}



cout << endl << "----- Testing access to characters (using non-const)"
<< endl;
MyString s2("abcdefghijklmnopqsrtuvwxyz");
cout << "Start with " << s2;
for (int i = 0; i < s.length(); i++){
s2 = toupper(s2);
}
cout << " and convert to " << s2 << endl;
}









void RelationTest()
{
cout << "\n----- Testing relational operators between MyStrings\n";

const MyString strs[] =
{MyString("app"), MyString("apple"), MyString(""),
MyString("Banana"), MyString("Banana")};

for (int i = 0; i < 4; i++) {
cout << "Comparing " << strs << " to " << strs[i+1] << endl;
cout << "\tIs left < right? " << (strs < strs[i+1]) << endl;
cout << "\tIs left <= right? " << (strs <= strs[i+1]) << endl;
cout << "\tIs left > right? " << (strs > strs[i+1]) << endl;
cout << "\tIs left >= right? " << (strs >= strs[i+1]) << endl;
cout << "\tDoes left == right? " << (strs == strs[i+1]) << endl;
cout << "\tDoes left != right ? " << (strs != strs[i+1]) << endl;
}

cout << "\n----- Testing relations between MyStrings and char *\n";
MyString s("he");
const char *t = "hello";
cout << "Comparing " << s << " to " << t << endl;
cout << "\tIs left < right? " << (s < t) << endl;
cout << "\tIs left <= right? " << (s <= t) << endl;
cout << "\tIs left > right? " << (s > t) << endl;
cout << "\tIs left >= right? " << (s >= t) << endl;
cout << "\tDoes left == right? " << (s == t) << endl;
cout << "\tDoes left != right ? " << (s != t) << endl;

MyString u("wackity");
const char *v = "why";
cout << "Comparing " << v << " to " << u << endl;
cout << "\tIs left < right? " << (v < u) << endl;
cout << "\tIs left <= right? " << (v <= u) << endl;
cout << "\tIs left > right? " << (v > u) << endl;
cout << "\tIs left >= right? " << (v >= u) << endl;
cout << "\tDoes left == right? " << (v == u) << endl;
cout << "\tDoes left != right ? " << (v != u) << endl;

}




void ConcatTest()
{
cout << "\n----- Testing concatentation on MyStrings\n";

const MyString s[] =
{MyString("outrageous"), MyString("milk"), MyString(""),
MyString("cow"), MyString("bell")};

for (int i = 0; i < 4; i++) {
cout << s << " + " << s[i+1] << " = " << s + s[i+1] << endl;
}

cout << "\n----- Testing concatentation between MyString and char *\n";

const MyString a("abcde");
const char *b = "XYZ";
cout << a << " + " << b << " = " << a + b << endl;
cout << b << " + " << a << " = " << b + a << endl;

cout << "\n----- Testing shorthand concat/assign on MyStrings\n";

MyString s2[] =
{MyString("who"), MyString("what"), MyString("WHEN"),
MyString("Where"), MyString("why")};

for (int i = 0; i < 4; i++) {
cout << s2 << " += " << s2[i+1] << " = ";
cout << (s2 += s2[i+1]) << endl;
}

cout << "\n----- Testing shorthand concat/assign using char *\n";
MyString u("I love ");
const char *v = "programming";
cout << u << " += " << v << " = ";
cout << (u += v) << endl;
}









MyString AppendTest(const MyString& ref, MyString val)
{
val[0] = 'B';
return val + ref;
}







void CopyTest()
{
cout << "\n----- Testing copy constructor and operator= on MyStrings\n";

MyString orig("cake");


MyString copy(orig); // invoke copy constructor

copy[0] = 'f'; // change first letter of the *copy*
cout << "original is " << orig << ", copy is " << copy << endl;


MyString copy2; // makes an empty string

copy2 = orig; // invoke operator=
copy2[0] = 'f'; // change first letter of the *copy*
cout << "original is " << orig << ", copy is " << copy2 << endl;

copy2 = "Copy Cat";
copy2 = copy2; // copy onto self and see what happens
cout << "after self assignment, copy is " << copy2 << endl;


cout << "Testing pass & return MyStrings by value and ref" << endl;
MyString val = "winky";
MyString sum = AppendTest("Boo", val);
cout << "after calling Append, sum is " << sum << endl;
cout << "val is " << val << endl;
val = sum;
cout << "after assign, val is " << val << endl;

}





MyString::MyString()
{

string = new char[0];
string[0] = 0;

}






MyString::MyString(const char *inString)
{
string = new char[strlen(inString)+1];
strcpy(string,inString);
}






MyString::~MyString()
{
delete []string;
}




ostream& operator<<(ostream &out,const MyString &outString)
{
out<<outString.string;
return out;
}






MyString MyString:: operator=(const MyString right)
{
if (this != &right)
{
delete []string;
string = new char[strlen(right.string)+1];
strcpy(string,right.string);
}
return *this;
}






MyString::MyString(const MyString &right)
{
string = new char[strlen(right.string)+1];
strcpy(string,right.string);
}







char& MyString:perator[](int index)
{
assert(index>=0 && index < strlen(string));
return string[index];
}








char MyString:perator[](int index)const
{
assert(index>=0 && index < strlen(string));
return string[index];
}



istream& operator>>(istream& in,MyString &inString)
{

char temp[128];
delete [] inString.string;
in>>temp;
strcpy(inString.string,temp);

return in;
}


void MyString::read(istream &inString,char delimit)
{
char temp[128];
delete []string;
inString.getline(temp,127,delimit);
strcpy(string,temp);
}

MyString operator+(const MyString left,const MyString right)
{
MyString temp;
//temporary mystring to hold contents of left.string+right.string
temp.string = new char[strlen(left.string)+strlen(right.string)+1];
//dynamic array size of left.string+right.string+1
strcat(left.string,right.string);
//make left.string+right.string into left.string
strcpy(temp.string,left.string);
//copy the contents of left.string into temp.string;
return temp;
//return the copy of MyString temp
}


MyString& MyString :: operator+=(const MyString &right)
{
*this = *this+right;
return *this;
}


int MyString::length()const
{

return strlen(string);

}


bool operator<(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) < 0;
}

bool operator<=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) <= 1;
}


bool operator>(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) > 0;
}


bool operator>=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) >= 1;
}



bool operator==(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) == 1;
}

bool operator!=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) != 1;
}

 

[Karl Heinz Buchegger]

Below is my project. My Code is done, but when I try to compile it, my IDE
crahses (again). I fixed up all the things you guys said I should, except
for some which would not meet the project requiremnts. here is my code. it
compiles, but crashes winsioux.

Learn to use a debugger.
I compiled your program and run it under the debugger.
The first crash happens in ...

istream& operator>>(istream& in,MyString &inString)
{

char temp[128];
delete [] inString.string;

^
.... at this line |

which is a string indication that something with the way you allocate
memory is flawed. So lets look at the constructor first:

MyString::MyString()
{

string = new char[0];
string[0] = 0;

}

Oha. You allocate allocate an array of size 0 (which is legal)
but yet assign a value to an imaginary first array element.
If an array has size 0, then there is no element 0. If an
array has as its only element the element 0, then it has
size 1 (as there is one element in the array).
Remember: The biggest valid index into an array is always
1 less then the size of the array (since counting starts at 0)

string = new char[ 1 ];
string[0] = 0;

OK. First bug fixed. Recompile, starting the debugger.

The next crash happens, when in the loop:

while (!eof(in)) {
MyString s; // creates an empty string
if (in.peek() == '#') { // peek at char, comments start with #
in.ignore(128, '\n'); // skip this line, it's a comment
} else {
in >> s;
cout << "Read string = " << s << endl;
}
}

the variable s goes out of scope. Again it has something to do with
memory management, since th crash happens deep in systems code, which
originated at delete. So lets look at the history of s:
It has been created, then operator>> assigns a new value to it and
then it gets deleted. Fine. The ctor is correct, so the problem must
be in operator>>. Lets take a closer look:

in>>temp;
strcpy(inString.string,temp);

return in;
}

void MyString::read(istream &inString,char delimit)
{
char temp[128];
delete []string;
inString.getline(temp,127,delimit);
strcpy(string,temp);
}

MyString operator+(const MyString left,const MyString right)
{
MyString temp;
//temporary mystring to hold contents of left.string+right.string
temp.string = new char[strlen(left.string)+strlen(right.string)+1];
//dynamic array size of left.string+right.string+1
strcat(left.string,right.string);
//make left.string+right.string into left.string
strcpy(temp.string,left.string);
//copy the contents of left.string into temp.string;
return temp;
//return the copy of MyString temp
}

MyString& MyString :: operator+=(const MyString &right)
{
*this = *this+right;
return *this;
}

int MyString::length()const
{

return strlen(string);

}

bool operator<(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) < 0;
}

bool operator<=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) <= 1;
}

bool operator>(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) > 0;
}

bool operator>=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) >= 1;
}

bool operator==(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) == 1;
}

bool operator!=(const MyString &left, const MyString &right)
{
return strcmp(left.string,right.string) != 1;
}

--
Karl Heinz Buchegger, GASCAD GmbH
Teichstrasse 2
A-4595 Waldneukirchen
Tel ++43/7258/7545-0 Fax ++43/7258/7545-99
email: (e-mail address removed) Web: www.gascad.com

Fuer sehr grosse Werte von 2 gilt: 2 + 2 = 5

 

[Karl Heinz Buchegger]

Karl Heinz Buchegger wrote:

Sorry. Hit Send by accident.

Below is my project. My Code is done, but when I try to compile it, my IDE
crahses (again). I fixed up all the things you guys said I should, except
for some which would not meet the project requiremnts. here is my code. it
compiles, but crashes winsioux.

Learn to use a debugger.
I compiled your program and run it under the debugger.
The first crash happens in ...

istream& operator>>(istream& in,MyString &inString)
{

char temp[128];
delete [] inString.string;

^
... at this line |

which is a string indication that something with the way you allocate
memory is flawed. So lets look at the constructor first:

MyString::MyString()
{

string = new char[0];
string[0] = 0;

}

Oha. You allocate allocate an array of size 0 (which is legal)
but yet assign a value to an imaginary first array element.
If an array has size 0, then there is no element 0. If an
array has as its only element the element 0, then it has
size 1 (as there is one element in the array).
Remember: The biggest valid index into an array is always
1 less then the size of the array (since counting starts at 0)

string = new char[ 1 ];
string[0] = 0;

OK. First bug fixed. Recompile, starting the debugger.

The next crash happens, when in the loop:

while (!eof(in)) {
MyString s; // creates an empty string
if (in.peek() == '#') { // peek at char, comments start with #
in.ignore(128, '\n'); // skip this line, it's a comment
} else {
in >> s;
cout << "Read string = " << s << endl;
}
}

the variable s goes out of scope. Again it has something to do with
memory management, since th crash happens deep in systems code, which
originated at delete. So lets look at the history of s:
It has been created, then operator>> assigns a new value to it and
then it gets deleted. Fine. The ctor is correct, so the problem must
be in operator>>. Lets take a closer look:

istream& operator>>(istream& in,MyString &inString)
{

char temp[128];
delete [] inString.string;
in>>temp;
strcpy(inString.string,temp);

return in;
}

Oha.
I can see, that you delete inString.string
But i can't see where new memory is allcoated. Thus
the strcpy copies the characters to memory which
no longer belongs to the program. Worse then that
when the time has come for the dtor to delete the memory,
it will delete the same memory twice.
Lets fix that:

char temp[128];
delete [] inString.string;
in>>temp;
inString.string = new char [ strlen( temp ) + 1 ];
strcpy(inString.string,temp);

return in;
}

Besides: your usage of eof in the reading loop is wrong. See the
FAQ to figure out why.

OK. Fixing the bug, recompile and starting the debugger takes just
a couple of seconds.

The next bug happens in the next loop:

cout << endl << "----- now, line by line" << endl;
ifstream in2("string.data");
assert(in2);
while (!eof(in2)) {
MyString s; // creates an empty string
if (in2.peek() == '#') { // peek at char, comments start with #
in2.ignore(128, '\n'); // skip this line, it's a comment
} else {
s.read(in2, '\n');
cout << "Read string = " << s << endl;
}
}
in2.close();

Same symptoms: The crash happens when variable s goes out of scope. With the
experience from the previous bug, I immediatly acuse function MyString::read

void MyString::read(istream &inString,char delimit)
{
char temp[128];
delete []string;
inString.getline(temp,127,delimit);
strcpy(string,temp);
}

Same problem: you delete but don't allocate.

inString.getline(temp,127,delimit);
string = new char [ strlen( temp ) + 1 ];
strcpy(string,temp);


Fixing the bug and starting the debugger again takes a couple of seconds.
And on we go, the next crash happens in:

MyString operator+(const MyString left,const MyString right)
{
MyString temp;
//temporary mystring to hold contents of left.string+right.string
temp.string = new char[strlen(left.string)+strlen(right.string)+1];
//dynamic array size of left.string+right.string+1
strcat(left.string,right.string);
//make left.string+right.string into left.string
strcpy(temp.string,left.string);

Hmm. HOw can you strcat something to left.string.
left.string has still its old size, and since your array sizes
are always tailored to what is needed, this is definitly to short
to store the result of the strcat.

I guess you ment:

strcpy( tmp.string, left.string );
strcat( tmp.string, right.string );

Fixing that bug and starting the debugger again takes a couple of seconds.
And on we go, the next crash happens ...

No more crashes.

All i nall I have to say you made a typical newbie mistake.
You wrote too much code without intermediate testing. Write
*one* function, write *one* operator and test it! Only after
that new function works as expected add the next one.

 

[Oplec]

I tried to perform my first debugging of code. I used the debugger in
Dev-C++ on the OP code and the debugger would just cancel. For some reason
when the debugger is run it will run the entire program, and since the
program aborts, I wasn't able to debug it. The debugger was only useful on
my bug-free program and allowed me to follow instructions.

Which debugger did you use, and do you know how I might get the Dev-C++
working?

Thanks, Oplec.

 

[Samuele Armondi]

I tried to perform my first debugging of code. I used the debugger in
Dev-C++ on the OP code and the debugger would just cancel. For some reason
when the debugger is run it will run the entire program, and since the
program aborts, I wasn't able to debug it. The debugger was only useful on
my bug-free program and allowed me to follow instructions.

Which debugger did you use, and do you know how I might get the Dev-C++
working?

Thanks, Oplec.

Step into the code, run it one line at a time. Or use breakpoints and
examine the variables as you go.
HTH
S. Armondi