c++ - Why do compilers allow string literals not to be const?

Question

And where are literals in memory exactly? (see examples below)

I cannot modify a literal, so it would supposedly be a const char*, although the compiler let me use a char* for it, I have no warnings even with most of the compiler flags.

Whereas an implicit cast of a const char* type to a char* type gives me a warning, see below (tested on GCC, but it behaves similarly on VC++2010).

Also, if I modify the value of a const char (with a trick below where GCC would better give me a warning for), it gives no error and I can even modify and display it on GCC (even though I guess it is still an undefined behavior, I wonder why it did not do the same with the literal). That is why I am asking where those literal are stored, and where are more common const supposedly stored?

const char* a = "test";
char* b = a; /* warning: initialization discards qualifiers 
  from pointer target type (on gcc), error on VC++2k10 */

char *c = "test"; // no compile errors
c[0] = 'p'; /* bus error when execution (we are not supposed to 
  modify const anyway, so why can I and with no errors? And where is the 
  literal stored for I have a "bus error"? 
  I have 'access violation writing' on VC++2010 */

const char d = 'a';
*(char*)&d = 'b'; // no warnings (why not?)
printf("%c", d);  /* displays 'b' (why doesn't it do the same
  behavior as modifying a literal? It displays 'a' on VC++2010 */

Answer 1

The C standard does not forbid the modification of string literals. It just says that the behaviour is undefined if the attempt is made. According to the C99 rationale, there were people in the committee who wanted string literals to be modifiable, so the standard does not explicitly forbid it.

Note that the situation is different in C++. In C++, string literals are arrays of const char. However, C++ allows conversions from const char * to char *. That feature has been deprecated, though.