Re: No warning at implicit removal of const. Was: relearning C: why does an in-place change to a char* segfault?

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

candycanearter07 <candycanearter07@candycanearter07.nomail.afraid>
writes:

David Brown <david.brown@hesbynett.no> wrote at 17:56 this Thursday (GMT):

[...]
>

gcc has the option "-Wwrite-strings" that makes string literals in
C have "const char" array type, and thus give errors when you try
to assign to a non-const char * pointer.  But the option has to be
specified explicitly (it is not in -Wall) because it changes the
meaning of the code and can cause compatibility issues with
existing correct code.

>
-Wwrite-strings is included in -Wpedantic.

>
No it isn't, nor is it included in -Wall -- and it wouldn't make
sense to do so.
>
The -Wpedantic option is intended to produce all required
diagnostics for the specified C standard.  -Wwrite-strings
gives string literals the type `const char[LENGTH]`, which
enables useful diagnostics but is *non-conforming*.

>
As long as the -Wwrite-strings diagnostics are only warnings the
result is still conforming.

It's not just about diagnostics.  This program:

#include <stdio.h>
int main(void) {
    puts(_Generic("hello",
                  char*: "char*",
                  const char*: "const char*",
                  default: "?"));
}

must print "char*" in a conforming implementation.  With
(gcc|clang) -Wwrite-strings, it prints "const char*".

And something as simple as:

    char *p = "hello";

is rejected with a fatal error with "-Wwrite-strings -pedantic-errors".

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */