C++ Operator overloading, my own string class

Question

I'm trying to make my own string class in c++11 but I have some problems. comparing my class to the std::string class, I can't figute out how to use the

std::string.at(int) = 'a'; method/overloading.

I've created the at(int) method in my own class:

int at(int index)
{
    if(index <0 || index > size-1) {throw std::out_of_range("Error, index out of range");}
    return data[index];
}

and it workd well if I only use:

MyString.at(2);

In the main file:

MyString = "Hello world!"; //Works fine!
MyString.at(2)='a'; //Gives, Error: expressino must be a modifiable Ivalue.

Any help with this would be great, Thanks!

This is not the problem, but index > size-1 can be written more idiomatically as index >= size. — Pete Becker
– Pete Becker, Commented Oct 19, 2013 at 22:22

score 3 · Accepted Answer · 2013-10-19 21:45:44Z

3

At least one of your at() member functions needs to return a non-const reference to char. Like this:

char &at(std::size_t idx)
{
    return data[idx];
}

It would be beneficial to define a const version of the function too:

const char &at(std::size_t idx) const
{
    return data[idx];
}

Also note the use of std::size_t (which is an unsigned type guaranteed to be large enough to represent any size). This way you improve portability and you don't have to check for negative indices.

edited Oct 19, 2013 at 21:45

answered Oct 19, 2013 at 21:33

user529758

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4 Comments

Qaz Over a year ago

It might also be wise to have a const version.

user2774429 Over a year ago

Now I see the obvious problem! Thank you for your help!

user529758 Over a year ago

@chris Fair enough. Do you mean that the member function itself should be const or the return value should be a reference-to-const char? (The former makes more sense, just checking.)

Qaz Over a year ago

@H2CO3, Same as the subscripting operator overloads. Both combined.

Daniel Frey · Accepted Answer · 2013-10-19 21:33:02Z

1

You are returning an integer and not a reference to the character, you probably want:

char& at(int index)

Of course, you need to return the correct character type, but in any case you need to return a reference in order for the caller to be able to assign to it.

answered Oct 19, 2013 at 21:33

Daniel Frey

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1 Comment

user2774429 Over a year ago

Owooo.. how stupid I feel! Thank you for your answer!

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