C++ string and overloaded operators -

i'm studying c++ library type string. looking operation type can perform, among concatenation. know in c++ operators can overloaded suit class types needs,and know character string literals const char arrays under hood. so, know string type defines constructor takes string literal argument , converts string, can initialize string using:

string s="hello!" 

what happens here impicit conversion (through constructor takes const char*) string , copy initialization performed (through copy-constructor of string).

so far good.. (correct me if getting wrong far)

now, know can concatenate 2 strings, or can concatenate string , char literal (or vice versa) , string , string literal (so suppose first happens because there's overloaded + operator takes symmetrically char , string, latter happens overloaded + opeartor concatenates 2 strings , implicit conversion const char* string). questions are:

1: why can't concatenate 2 string literals? shouldn't operator+ takes 2 strings called (and 2 implicit conversion performed const char* string) ?

string s="hi"+" there"; 

2: tried concatenate char literal , string literal (calling operator+ takes char , string) garbage in resulting string, compiler doesn't mind, result not want.

string s='h'+"ello!"; cout<<s<<endl; 

i garbage out.if operator+(char,const string&) exists should called after implicitly converting "ello" string shouldn't it?

can please explain?

1) concatenating 2 string literals.

"hello" + " world" 

the compiler has no hint should looking related std::string -- looking @ 2 const char[] objects, , cannot + (or const char * degraded to).

2) using operator+ on char literal , string literal.

(thanks user dyp pointing in right direction.)

if literally mean char literal -- e.g. 'a' -- you're running afoul of 1 of more surprising things c/c++ have offer.

consider: a[i] equivalent i[a]. (this fact.)

so, if write:

'a' + "hello" 

...that equivalent (in ascii)...

"hello" + 97 

...which pointer nowhere, i.e. constructing std::string undefined behaviour.