Xcode C ++ development, clarifications needed

Question

I really like how Xcode offers to understand the possible available member functions of the language and would prefer to use it relative to, say, a text mat, if not for the strangeness that I noticed today.

When string s = "Test string"; only substr signature is available as shown

From what I understand and what I see online , the signature should be

 string substr ( size_t pos = 0, size_t n = npos ) const; 

Indeed s.substr(1,2) ; understood and works in Xcode.

Why is it not showing when I try to complete the method? (Ctrl-space)

Answer 1

Xcode completes correctly, but that is not what you expect. You actually answered the question without knowing. The function signature for the string substr() method, as you said, is:

 string substr ( size_t pos = 0, size_t n = npos ) const; 

All substr() arguments have default assignments, so for Xcode, s.substr() (without arguments), code completion for insertion is valid because it is really s.substr(0, s.npos) . You can confirm this with any number of standard C ++ functions with default arguments. The easiest way to see this is with any STL container constructor.

Take, for example, a vector . We all know that vectors can accept Allocator , but the default argument assigned by Allocator is "good enough" for most random purposes. Of course, two of the signatures for the vector constructors are:

 explicit vector ( const Allocator& = Allocator() ); explicit vector ( size_type n, const T& value= T(), const Allocator& = Allocator() ); 

In both cases, the Allocator argument has a default assignment, and in the second, the T value has a default assignment. Now let's see what Xcode offers when building vector :

A sentence without a list of arguments is actually a constructor that accepts only Allocator . A sentence that takes only a size_type is actually a constructor that accepts size_type , T and Allocator .

Depending on how you think about it, this may or may not be an Xcode error. Ideally, you want to see add-ons with default arguments for simpler functions like substr() , but for STL container constructors, you probably almost never want to see them. Perhaps this may be an option, but I did not expect this to be fixed. I would gladly please you with a radar.