Trying to make my own string class - c++

Question

These are the errors I'm getting for my program.
myString1.cpp: In constructor ‘MyString1::MyString1(char*, int)’:
myString1.cpp:6: error: expected primary-expression before ‘]’ token
myString1.cpp:6: error: expected primary-expression before ‘]’ token
myString1.cpp: In member function ‘MyString1 MyString1::append(MyString1)’:
myString1.cpp:11: error: invalid use of member (did you forget the ‘&’ ?)
myString1.cpp: In member function ‘void MyString1::clear()’:
myString1.cpp:25: error: expected primary-expression before ‘]’ token
myString1.cpp:25: error: expected primary-expression before ‘{’ token
myString1.cpp:25: error: expected `;' before ‘{’ token
myString1.cpp: In member function ‘bool MyString1::empty()’:
myString1.cpp:29: error: expected primary-expression before ‘]’ token
myString1.cpp:31: error: expected primary-expression before ‘else’
myString1.cpp:31: error: expected `;' before ‘else’
And here is my program in the three different parts.
myString1.h
#ifndef MYSTRING1_H
#define MYSTRING1_H
class MyString1
{
private:
char chars[];
int size;
public:
MyString1();
MyString1(char chars[], int size);
MyString1 append(MyString1 s);
char at(int index);
int length();
void clear();
bool empty();
int find(char ch);
};
#endif
myString1.cpp
#include "myString1.h"
using namespace std;
MyString1::MyString1(char chars[], int size)
{
this->chars[] = chars[];
this->size = size;
}
MyString1 MyString1::append(MyString1 s)
{
for(int i = size; i > size - s.length; i++)
chars[i] = s.at(i);
}
char MyString1::at(int index)
{
return chars[index];
}
int MyString1::length()
{
return size;
}
void MyString1::clear()
{
size = 0;
chars[] = {};
}
bool MyString1::empty()
{
if(chars[]){
return true;
else
return false;
}
}
int MyString1::find(char ch)
{
for(int i = 0; i < size; i++)
if(chars[i] = ch)
return i;
}
testMyString1.cpp
#include <iostream>
#include "myString1.h"
using namespace std;
int main()
{
MyString1 first("cat", 4);
MyString1 second("dog", 4);
cout << first.at(1) << " and " << second.at(1) << endl;
first.append(second);
cout << first.at(6) << endl;
return 0;
}
Im a newbie just trying to learn how to use the g++ compiler so just looking for some help reading the error messages and debugging my code. Also I'm sure there is some very bad code so any help is appreciated.

Answer 1

The code has a lot of mistakes so I don't know where to start from but I suppose that generally giving you some pointers to help you with understanding your code would be okay.
In my opinion you don't need to have a size index in a String class since there is the strlen() function that will gladly compute it for you.
Now for your class declaration check how you declare the pointer that will hold the string for you. You need to do it like below:
class MyString1
{
private:
char* chars;//this declares a pointer to a char that will hold the string for you
public:
...
Also you are never allocating the char* that holds the strings. Your constructor should be:
MyString1::MyString1(const char* chars)
{
this->chars = (char*) malloc(strlen(chars)+1); //this will allocate an array of strlen() chars +1
strcpy(this->chars,chars);
}
As you can see I am not using a size index since strlen can quite efficiently find that out for you. +1 is for the '\0' that signifies the end of a string.
Now to append something to the string, that's gonna be tricky.
void MyString1::append(const MyString1& s) //it's good to give a constant reference to the string here
{
//first of all we gotta reallocate the pointer,since we don't have enough memory for the string
int newsize = strlen(this->chars) + strlen(s)+1;
this->chars = (char*) realloc(this->chars,newSize); \\ no check for realloc failure, I know but this is just an example
strcat(this->chars,s.chars);
}
You don't need to return anything when you append. You are doing something to THIS string.
Your ::at() function is almost okay. Imagine though what would happen if the size of the string was 10 and you request MyString1::at(12). This would probably cause a Segmentation fault (that's not good).
So you should alter your code to do bounds checking like below:
char MyString1::at(int index)
{
//if it's out of bounds let's return -1 which will signify that we got an out of bounds value (could also throw an exception here but that's a different subject altogether)
if(index > strlen(this->chars) || index <0)
return -1;
return chars[index];
}
Also in C/C++ you have to free the memory that you allocate. So in order to do that you should declare something called a destructor
MyString1::~MyString1()
{
free(this->chars);
}
Finally the is empty function can just be like that:
bool MyString1::empty()
{
return (this->chars[0] == '\0';
}