C++ / Operator overloading / Compiler Error

DeadBankClerk · 29-11-2002 04:36PM #1

This syntax error has two friends and myslef absolutely stumped. The three of us are in third year computer science and we cant fix a c++ syntax error.

:rolleyes:

String.h
[php]#ifndef __String__
#define __String__

namespace marc
{

class String
{
private:
int len; // Length of the String
char* data; // Pointer to the array of characters

public:
String (void); // Default constructor
String (const char* s); // Character array constructor
String (const String &other); // Copy constructor
~String (void); // Destructor

private:
String (const String &one, const String &two); // Concat Constructor

public:

operator char*() const; // Cast this to a char pointer

String operator = (const String &other) const;
String operator + (const String &other) const;
bool operator == (const String &other) const;
bool operator < (const String &other) const;
bool operator <= (const String &other) const;
bool operator > (const String &other) const;
bool operator >= (const String &other) const;

bool valid_index (const int i) const;
int index_of (const char c, const int start_index = 0) const;
bool has (const char c) const;
void clear (void);

};
}

#endif
[/php]

String.cpp
[php]
#include <string.h>
#include "String.h"
#include <iostream.h>

using namespace marc;

String::String (void)
{
this->len = 0;
this->data = new char[1];
this->data[0] = 0;
}

String::String (const char* s)
{
this->len = strlen(s);
this->data = new char [len+1];
for (int i = 0; i < this->len; i++)
{
this->data = s;
}
this->data[len] = 0;
}

String::String (const String &other)
{
this->len = other.len;
this->data = new char[len+1];
for (int i = 0; i < this->len; i++)
{
this->data = other.data;
}
this->data[len] = 0;
}

String::String (const String &one, const String &two)
{
int i;
this->len = one.len + two.len;
this->data = new char[this->len + 1];

for (i = 0; i < one.len; i++)
{
this->data = one.data;
}
for (; i < this->len; i++)
{
this->data = two.data;
}
}

String::~String (void)
{
delete [] this->data;
}

bool String::valid_index (const int i) const
{
return (0 <= i) && (i < len);
}

int String::index_of (const char c, const int start_index = 0) const
{
for (int i = start_index; i < len; i++)
{
if (this->data == c) return i;
}
}

void String::clear (void)
{
for (int i = 0; i <= len; i++)
{
this->data = 0;
}
}

bool String::has (const char c) const
{
for (int i = 0; i < this->len; i++)
{
if (data == c) return true;
}
return false;
}

String::operator char*() const
{
return this->data;
}

String String::operator = (const String& other) const
{
return String(other);
}

String String::operator + (const String& other) const
{
return String(*this, other);
}

bool String::operator ==(const String& other) const
{
return (strcmp(this->data, other.data) == 0);
}

bool String::operator < (const String& other) const
{
return (strcmp(this->data, other.data) == -1);
}

bool String::operator <= (const String& other) const
{
return (strcmp(this->data, other.data) < 1);
}

bool String::operator > (const String& other) const
{
return (strcmp(this->data, other.data) == 1);
}

bool String::operator >= (const String& other) const
{
return (strcmp(this->data, other.data) > -1);
}

bool unit_test(void)
{
String s1 ();
String s2 ("Hello world");
String s3 ("Hello world");
String s4 ("Hello nurse");

bool OperatorEqualsEquals = (s2 == s3);
return OperatorEqualsEquals;
}

using namespace std;

int main(void)
{
marc::String passed("Passed");
marc::String failed("Failed");

cout << "Class String test: ";
unit_test() ? cout << passed : cout << failed;
cout << endl << flush;

return 1;
}

[/php]

Compiler error:

3:29pm dbc@matrix [~/files]> g++ -o String String.cpp
String.cpp: In function `bool unit_test()':
String.cpp:138: no matching function for call to
`marc::String::operator==(marc::String (&)())'
String.cpp:107: candidates are: bool marc::String::operator==(const
marc::String&) const

Can anyone see why it wont let me use the == operator?

satchmo · 29-11-2002 05:22PM

I think it's your namespaces are screwing things up. I tried it without all the namespace stuff and it compiled & ran fine (unit_test passed). I don't use namespaces though so past telling you what the problem is, I can't really offer any solution.

[edit] On second try, I put back in the namespace stuff, but it was complaining that 'std : does not exist or is not a namespace', so i took out the line using namespace std and it worked fine

[/edit]

Typedef · 29-11-2002 05:34PM

Perhaps

marc::String:: operator ==

would work in that case.

DeadBankClerk · 29-11-2002 07:19PM

I have founf the error. I was makeing a marc::String object s1 by declaring it

String s1 ();

I should have been declaring:
String s1;

The empty parenthesis dont call the correct constructor apperently

I have fixed it now, although i wasted an hour of my life

SkepticOne · 29-11-2002 08:28PM

I copied the code and compiled but got completely different errors:

[b]$ g++ String.cpp -o String[/b]

String.cpp:133: default argument given for parameter 2 of `int 
   marc::String::index_of(char, int = 0) const'
String.h:69: after previous specification in `int marc::String::index_of(char, 
   int = 0) const'

This was fixed by removing the default argument in the implemetation of String::index_of(... in String.cpp and leaving it in the declaration in the header file.

Following that I get the output:

"Class String test: Passed"

I'm using cpp-3.2.1, btw. This apparently is more standards complient than older versions.

C++ / Operator overloading / Compiler Error

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