Need help, String Class

[Merriak]

Hi,

I have an assignment to make my own string class and to avoid using the c++ string class. I'm just about done, but I am getting the following error when I try to compile.

string_test.cpp: In function ‘int main()’:
string_test.cpp:23: error: no match for ‘operator=’ in ‘s3 = "bye"’
string.h:26: note: candidates are: void String::operator=(String&)
string_test.cpp:29: error: no match for ‘operator+=’ in ‘s1 += "re"’
string.h:27: note: candidates are: void String::operator+=(String&)
string_test.cpp:32: error: no match for ‘operator+=’ in ‘s1 += "d"’
string.h:27: note: candidates are: void String::operator+=(String&)

Here's my code, I can't understand why it's not finding a match for those operators when I have them declared in my class code?

string.h

#ifndef STRING_H
#define STRING_H

// String.h

#include <iostream>

using namespace std;

class String {
    int size;
    char * buffer;
public:
    String();
    String(const String & s);
    String(const char* s);
    ~String();
    
    //functions
    int length();
    void resize(unsigned int, char);
    void insert(unsigned int, String&);
    
    //operators
    char& operator[](unsigned int);
    void operator = (String &);
    void operator += (String &);
    
    
    friend bool operator==(const String &, const String &);
    friend bool operator<=(const String &, const String &);
    friend bool operator<(const String &, const String &);
    friend ostream & operator<<(ostream &, const String &);
};

#endif 

string.cpp

#include "string.h"
#include <cassert>
using namespace std;

String::String()
{
    buffer = 0;
    resize(0, ' ');
}

String::String(const String& s)
{
    size = s.size;
    buffer = new char[size];
    for(int i = 0; i < size; i++){
        buffer[i] = s.buffer[i];
    }
}

String::String(const char *p)
{
    int p_size = 0;
    for(const char *q = p; *q; q++){
        p_size++;
    }
    buffer = new char[p_size];
    for(int i=0;i<p_size;i++){
        size = p_size;
    }
}

String::~String()
{
    delete[] buffer;
}

int String::length()
{
    int i = 0;
    while(buffer[i] != '\0'){
        i++;
    }
    return i;
}

void String::resize(unsigned int newlength, char pad)
{
    if (buffer == 0){
        size = 0;
    }
    if (newlength < size){
        buffer[newlength = '\0'];
    }
    else{
        int i;
        char * newbuffer = new char[newlength + 1];
        assert (newbuffer != 0);
        for(i=0; i < size && buffer[i] != '\0'; i++){
            newbuffer[i] = buffer[i];
        }
        for( ; i < newlength;i++){
            newbuffer[i] = pad;
        }
        newbuffer[i] = '\0';
        if(buffer != 0){
            delete[] buffer;
        }
        buffer = newbuffer;
        size = newlength; 
    }
}

void String::insert(unsigned int position, String &text)
{
    int lgt = length();
    int addlength = text.length();
    int newlength = lgt + addlength;
    resize(newlength, '\0');
    for(int i = lgt; i >= position; i--){
        buffer[i + addlength] = buffer[i];
    }
    for (int i = 0; i < addlength; i++){
        buffer[position + i] = text[i];
    }
}

char & String::operator[](unsigned int index)
{
    assert (index <= size);
    return buffer[index];
}

void String::operator = (String & p){
    resize(p.length(), ' ');
    strcpy(buffer, p.buffer);
}

void String::operator += (String & s){
    insert(length(), s);
}

bool operator==(const String &S1, const String &S2)
{
   	if(S1.size == S2.size)
	{
		int counter1 = S1.size;
		int counter2 = 0;
		int i = 0;
		while(i != counter1)
		{
			if(S1.buffer[i] != S2.buffer[i]){
                counter2++;
            }
			i++;
		}
		if(counter2 != 0) {
            return false;
        }
		else{
            return true;
        }
	}
	else {
        return false;
    }
}

bool operator<=(const String &S1, const String &S2){
    if(S1.size <= S2.size){
        int counter1 = S1.size;
        int counter2 = 0;
        int i = 0;
        while(i != counter1){
            if(S1.buffer[i] <= S2.buffer[i]){
                counter2++;
            }
            i++;
        }
        if(counter2 != 0){
            return true;
        }
        else{
            return false;
        }
    }
    else{
        return false;
    }
}

ostream& operator<< ( ostream& os, const String& s)
{
    
        os << s.size;
        return os;
    
}

string_test.cpp

#include "string.h"
#include <cassert>
#include <iostream>

using namespace std;

int main()
{
    String s1; // s1 == ""
    assert(s1.length() == 0);
    
    String s2("hi");  // s2 == "hi"
    assert(s2.length() == 2);
    
    String s3(s2);  // s3 == "hi"
    assert(s3.length() == 2);
    assert(s3[0] == 'h');
    assert(s3[1] == 'i');
    
    s1 = s2;  // s1 == "hi"
    assert(s1 == s2);
    
    s3 = "bye";  // s3 == "bye"
    assert(s3.length() == 3);
    assert(s3[0] == 'b');
    assert(s3[1] == 'y');
    assert(s3[2] == 'e');
    
    s1 += "re";  // s1 == "hire"
    assert(s1 == "hire");
    
    s1 += "d"; // s1 == "hired"
    assert(not (s1 == "hire"));
    
    cout << "SUCCESS" << endl;
}

Thanks for your help!

[ne555]

operator = (const String &);

[Merriak]

I've actually tried that, but it causes a second error when trying to compile string.cpp.

string.cpp: In member function ‘void String::operator=(const String&)’:
string.cpp:95: error: passing ‘const String’ as ‘this’ argument of ‘int String::length()’ discards qualifiers

[ne555]

check out `const correctness'
int length() const;

[Merriak]

Alright got it to compile! However my second assertion failed... :(

Assertion failed: (s2.length() == 2), function main, file string_test.cpp, line 13.
Abort trap: 6

Now to find out what's wrong.

[Merriak]

Yeah I did that ne! Thanks! Found I was missing several const.