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String class implementation

cppnoob25 (165)
For coding practice I am writing a String class based on something a professor gave us back when I took data structures. I am getting an error in my code and don't know how to fix it.

This is the erorr.

|104|error: passing 'const String' as 'this' argument of 'const int String::length()' discards qualifiers [-fpermissive]|

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#include <iostream>
#include <cassert>

using namespace std;

class String {
        int size;
        char * buffer;
public:
        String();
        String(const String &);
        String(const char *);
        ~String();
        int length();
        void resize(unsigned int, char);
        void insert(unsigned int, String&);
        char& operator[] (unsigned int);
        void operator =(const String&);
        void operator += (const String&);

        	// other methods
        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 &);
};

String::String()
{
    buffer = nullptr;
    size = 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 i = 0;
    const char * t = p;

    while(*p++)
    {
        i++;
    }

    buffer = new char[i];
    int j = 0;

    for(j;*t;t++,j++)
    {
        buffer[j] = *t;
    }
    size = j;
}

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

int String::length()
{
    if(buffer == nullptr)
    {
        return 0;
    }
    else
    {
        return size;
    }
}

char & String::operator[] (unsigned int x)
{
    return buffer[x];
}

void String::operator =(const String&s)
{
    buffer = s.buffer;

}

ostream & operator<<(ostream &os, const String &s)
{
    for(int i = 0; i < s.size; i++)
    {
        os << s.buffer[i];
    }
    return os;

}

bool operator==(const String & s, const String & t)
{
    if(s.length() != t.length())
    {
        return false;
    }
    else
    {
        for(int i = 0; i < s.length(); i++)
        {
            if(s.buffer[i] != t.buffer[i])
            {
                return false;
            }
        }
    }
    return true;

}


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;
*/
}
Last edited on
Alrededor (166)
Your length() function should be a const member function. Change line 14 to:

int length() const

and line 68 to:

int String::length() const

(The problem is that some of your operators take a const String and then call the length() function.)

I haven't look for any other errors.
Last edited on
ats15 (423)
For operator =, you need to copy the size as well
cppnoob25 (165)
Thanks for the help. It's working now.
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