Question

Can you do this?

char* func()
{
   char * c = "String";
   return c;
}

is “String” here a globally allocated data by compiler?

Answer 1

You can do that. But it would be even more correct to say:

const char* func(){
  return "String";
}

The c++ spec says that string literals are given static storage duration. I can’t link to it because there are precious few versions of the c++ spec online.
This page on const correctness is the best reference I can find.

Section 2.13.4 of ISO/IEC 14882 (Programming languages – C++) says:

1. A string literal is a sequence of characters (as defined in 2.13.2) surrounded by double quotes, optionally
   beginning with the letter L, as in “…” or L”…”. A string literal that does not begin with L is an ordinary
   string literal, also referred to as a narrow string literal. An ordinary string literal has type “array of n
   const char” and static storage duration (3.7), where n is the size of the string as defined below, and is
   initialized with the given characters. …

2. Whether all string literals are distinct (that is, are stored in nonoverlapping objects) is implementation defined.
   The effect of attempting to modify a string literal is undefined.