Question

I have a hard time understanding the difference between these three:

const char * f() {
  return "this is a test";
}

const char * g() {
  const char * str = "test again";
  return str;
}

const double * h() {
  const double a = 2.718;
  return &a;
}

I get a warning for the h(), as warning: address of local variable ‘a’ returned. Which makes sense, but I do not understand why the compiler (gcc -Wall) is ok with the f() and g() function.

• Isn’t there a local variable there?
• When and how does the pointer returned by f() or g() gets deallocated?

Answer 1

String literals are not stored in the local stack frame. They live in a fixed place in your executable. Contrast:

const char * g() {
  const char * p = "test again";
  return p;
}

with

const char * g() {
  const char a[] = "test again";
  return a;
}

In the former, the return value points to a fixed place in your executable. In the latter, the return value points to (a now invalid location in) the stack.