Question

my main concern is if i am doing this safely, efficiently, and for the most part doing it right.

i need a bit of help writing my implementation of a string class. perhaps someone could help me with what i would like to know?

i am attempting to write my own string class for extended functionality and for learning purposes. i will not use this as a substitute for std::string because that could be potentially dangerous. 😛

when i use std::cout to print out the contents of my string, i get some unexpected output, and i think i know why, but i am not really sure. i narrowed it down to my assign function because any other way i store characters in the string works quite fine. here is my assign function:

void String::assign(const String &s)
{
    unsigned bytes = s.length() + 1;

    // if there is enough unused space for this assignment
    if (res_ >= bytes)
    {
        strncpy(data_, s.c_str(), s.length()); // use that space
        res_ -= bytes;
    }
    else
    {
        // allocate enough space for this assignment
        data_ = new char[bytes];
        strcpy(data_, s.c_str()); // copy over
    }

    len_ = s.length(); // optimize the length
}

i have a constructor that reserves a fixed amount of bytes for the char ptr to allocate and hold. it is declared like so:

explicit String(unsigned /*rbytes*/);

the res_ variable simply records the passed in amount of bytes and stores it. this is the constructor’s code within string.cpp:

String::String(unsigned rbytes)
{
    data_ = new char[rbytes];
    len_ = 0;
    res_ = rbytes;
}

i thought using this method would be a bit more efficient rather than allocating new space for the string. so i can just use whatever spaced i reserved initially when i declared a new string. here is how i am testing to see if it works:

#include <iostream>

#include "./string.hpp"

int main(int argc, char **argv)
{
    winks::String s2(winks::String::to_string("hello"));
    winks::String s(10);

    std::cout << s2.c_str() << "\n" << std::endl;

    std::cout << s.unused() << std::endl;
    std::cout << s.c_str() << std::endl;
    std::cout << s.length() << std::endl;

    s.assign(winks::String::to_string("hello")); // Assign s to "hello".

    std::cout << s.unused() << std::endl;
    std::cout << s.c_str() << std::endl;
    std::cout << s.length() << std::endl;

    std::cout.flush();
    std::cin.ignore();

    return 0;
}

if you are concerned about winks::String::to_string, i am simply converting a char ptr to my string object like so:

String String::to_string(const char *c_s)
{
    String temp = c_s;
    return temp;
}

however, the constructor i use in this method is private, so i am forcing to_string upon myself. i have had no problems with this so far. the reason why i made this is to avoid rewriting methods for different parameters ie: char * and String

the code for the private constructor:

String::String(const char *c_s)
{
    unsigned t_len = strlen(c_s);
    data_ = new char[t_len + 1];
    len_ = t_len;
    res_ = 0;
    strcpy(data_, c_s);
}

all help is greatly appreciated. if i have no supplied an efficient amount of information please notify me with what you want to know and i will gladly edit my post.

edit: the reason why i am not posting the full string.hpp and string.cpp is because it is rather large and i am not sure if you guys would like that.

Answer 1

You have to make a decision whether you will always store your strings internally terminated with a 0. If you don’t store your strings with a terminating zero byte, your c_str function has to add one. Otherwise, it’s not returning a C-string.

Your assign function doesn’t 0 terminate. So either it’s broken, or you didn’t intend to 0 terminate. If the former, fix it. If the latter, check your c_str function to make sure it puts a 0 on the end.