Are you allowed to re-assign char* to a string literal? - c++

Question

This is quite normal:
[const] char *str = "some text";
But initialisation is not the same as reassignment and string literals are a bit of a special case. What are the rules if you try to do this:
[const] char *str = "some text";
str = "some other text";
Note before someone says "try it" I'm asking what the language spec says, not what my particular compiler does.

Answer 1

Let's repose your question as being assignment and reassignment to a const char*. This is because a string literal is a read-only array of characters terminated will \0, and compilers are lapse in allowing assignment of a string literal to a char*. C++11 explicitly forbids this.
Reassignment of a const char* to a different literal is permissible: there is no danger of a memory leak here since the strings will be stored in a read-only section of your compiled binary.

Answer 2

About char*
As of C++11 all of that code is illegal. String literals can only be binded to char const* or in general a [char] const array.
Notice that a char[] can be initialized with a string literal as per §8.5.2/1:
An array of narrow character type (3.9.1), char16_t array, char32_t array, or wchar_t array can be initialized by a narrow string literal, char16_t string literal, char32_t string literal, or wide string literal, respectively, or by an appropriately-typed string literal enclosed in braces (2.13.5). Successive characters of the value of the string literal initialize the elements of the array.
[Example:
char msg[] = "Syntax error on line %s\n";
shows a character array whose members are initialized with a string-literal. [...]
Previously char* was supported but considered deprecated. And anyway, modifications to the string via that char* were considered undefined behaviour.
As per §4.2/2 (pre-C++11):
A string literal (2.13.4) that is not a wide string literal can be converted to an rvalue of type “pointer to char”; a wide string literal can be converted to an rvalue of type “pointer to wchar_t”. In either case, the result is a pointer to the first element of the array. This conversion is considered only when there is an explicit appropriate pointer target type, and not when there is a general need to convert from an lvalue to an rvalue. [Note: this conversion is deprecated. See Annex D. ] For the purpose of ranking in overload resolution (13.3.3.1.1), this conversion is considered an array-to-pointer conversion followed by a qualification conversion (4.4). [Example: "abc" is converted to “pointer to const char” as an array-to-pointer conversion, and then to “pointer to char” as a qualification conversion. ]
About reassigning the pointer
Reassinging a char* or a char const* is perfectly fine. The const there refers to the character, not the pointer. To avoid reassigning you would need char* const and char const* const respectively.

Answer 3

First of all it would be correctly to write
const char *str = "some text";
^^^^^
because string literals in C++ have types of constant character arrays. For example string literal "some text" has type const char [10].
An array name used in expressions is implicitly converted to a pointer to its first element.
For example in this declaration
const char *str = "some text";
the string literal is implicitly converted to an object of type const char * and has value of the address of the first character of the string literal.
Pointers may be reassigned. The assignment operator may be used with pointers.
So you may write
const char *str = "some text";
str = "some other text";
Now pointer str is reassigned and points to to the first character of string literal "some other text".
However if you declare the pointer itself as a constant object as for example
const char * const str = "some text";
^^^^^
then in this case you may not reassigned it. The compiler will issue an error for statement
str = "some other text";