Thread: initialize conventions

(1) They both result in the same machine code, correct.

(1b)
With brackets you have to be careful, you can do:

Code:

std::string s{"Some string"}; // calls constructor just like s("Some string") would

It's also a general syntax to create objects, which the compiler can deduce:

Code:

std::string make_string()
{
    return {"Hello"}; // returns object: std::string("Hello");
    return {}; // returns empty std::string
}

It has the added property that it doesn't allow narrowing conversions:

Code:

double d = 5.0;
int n1(d); // fine
int n2{d}; // error, look at the message from your compiler

Edit: the entry form snipped away the rest of my post:

(2) Correct, str1 is a reference to const std::string, i.e. vows not to change the referenced object.

(3) Correct, a reference – once bound – cannot be unbound/rebound to something else, so a const specifier makes no sense but it would look like in your example.

It's worth mentioning that r-value references exist, which can bind to a temporary value (which prior only reference-to-const could) and even modify it over its lifetime:

Code:

std::string&& s = "Hello"; // r-value reference, notice the double &
s += " World!";
cout << s << endl; // Hello World!

Originally Posted by R_W_B

So there would never be a need to add the "const" to a "&" reference, correct (?)

Not exactly. In the case of references, the reference is const, but the referred object may not be. Adding const to the reference makes the referred object const.

Originally Posted by Guest

(1) . . . . . . .(RWB edit ->this part cut out, but thank you for the detailed confirmations) . . . .

(3) Correct, a reference – once bound – cannot be unbound/rebound to something else, so a const specifier makes no sense but it would look like in your example.

It's worth mentioning that r-value references exist, which can bind to a temporary value (which prior only reference-to-const could) and even modify it over its lifetime:

Code:

std::string&& s = "Hello"; // r-value reference, notice the double &
s += " World!";
cout << s << endl; // Hello World!

Originally Posted by Elkvis

Not exactly. In the case of references, the reference is const, but the referred object may not be. Adding const to the reference makes the referred object const.

Thank you both. However . . oh gawd . . I have distant nightmares of past yrs when I took a hiatus from learning programming about things done behind ctors and operators with lvalues and rvalues.

Something akin to when a hookah-smoking operator has returned you the call, go ask Alice what the dormouse said. (lol). Uh excuse an old man digressing as all those lyrics are quite possibly before your time.

But seriously you've answered my questions excellent and yet stretched me to the next horizon. Of the "whys" I have really no idea yet but I will read up on them again.