Re: [ANN] Lua 5.3.0 (rc2) now available

[Roberto Ierusalimschy <roberto@...>]

> > There is one warning on Mac OS X (10.10) when compiling in Xcode 6.1.1 with default warnings enabled:
> > 
> > /Users/jean-luc/Developpement/lua-5.3.0 - xcode/src/liolib.c:480:16: warning: variable 'c' may be uninitialized when used here [-Wconditional-uninitialized]
> >   if (!chop && c == '\n')  /* want a newline and have one? */
> >                ^
> > /Users/jean-luc/Developpement/lua-5.3.0 - xcode/src/liolib.c:467:8: note: initialize the variable 'c' to silence this warning
> >   int c;
> >        ^
> > This is a false positive, but hard for the compiler to detect that c is always initialized… :-)
> 
> It is not that hard: the only branch in the path from the function head
> to the first assignment to 'c' is obviously false (jump if not (0 <
> some-non-zero-constant)).  I am afraid that solving this warning with
> a useless initialization can generate warnings in smarter compilers
> ("value is never used"). I tried to change the code to make it more
> "obvious" that 'c' cannot be used uninitialized, but could not find a
> good solution.

You can try this, but in my view it is hardly an improvement...

--- liolib.c	2014/11/21 12:17:33	2.141
+++ liolib.c	2014/12/31 18:17:02
@@ -470,8 +470,11 @@
     char *buff = luaL_prepbuffer(&b);  /* pre-allocate buffer */
     int i = 0;
     l_lockfile(f);  /* no memory errors can happen inside the lock */
-    while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n')
+    do {
+      if ((c = l_getc(f)) == EOF || c == '\n')
+        break;
       buff[i++] = c;
+    } while (i < LUAL_BUFFERSIZE);
     l_unlockfile(f);
     luaL_addsize(&b, i);
     if (i < LUAL_BUFFERSIZE)


-- Roberto