Previously this file would fail to compile with the following error:
$ gcc manual/examples/mbstouwcs.c
manual/examples/mbstouwcs.c: In function ‘mbstouwcs’:
manual/examples/mbstouwcs.c:34:11: error: ‘errno’ undeclared (first use in this function)
34 | errno = EILSEQ;
| ^~~~~
manual/examples/mbstouwcs.c:5:1: note: ‘errno’ is defined in header ‘<errno.h>’; this is probably fixable by adding ‘#include <errno.h>’
4 | #include <wchar.h>
+++ |+#include <errno.h>
5 |
manual/examples/mbstouwcs.c:34:11: note: each undeclared identifier is reported only once for each function it appears in
34 | errno = EILSEQ;
| ^~~~~
manual/examples/mbstouwcs.c:34:19: error: ‘EILSEQ’ undeclared (first use in this function)
34 | errno = EILSEQ;
| ^~~~~~
manual/examples/mbstouwcs.c:47:20: error: implicit declaration of function ‘towupper’ [-Wimplicit-function-declaration]
47 | *wcp++ = towupper (wc);
| ^~~~~~~~
manual/examples/mbstouwcs.c:5:1: note: include ‘<wctype.h>’ or provide a declaration of ‘towupper’
4 | #include <wchar.h>
+++ |+#include <wctype.h>
5 |
manual/examples/mbstouwcs.c:47:20: warning: incompatible implicit declaration of built-in function ‘towupper’ [-Wbuiltin-declaration-mismatch]
47 | *wcp++ = towupper (wc);
| ^~~~~~~~
manual/examples/mbstouwcs.c:47:20: note: include ‘<wctype.h>’ or provide a declaration of ‘towupper’
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
The example did not work because the null byte was not converted, and
mbrtowc was called with a zero-length input string. This results in a
(size_t) -2 return value, so the function always returns NULL.
The size computation for the heap allocation of the result was
incorrect because it did not deal with integer overflow.
Error checking was missing, and the allocated memory was not freed on
error paths. All error returns now set errno. (Note that there is an
assumption that free does not clobber errno.)
The slightly unportable comparision against (size_t) -2 to catch both
(size_t) -1 and (size_t) -2 return values is gone as well.
A null wide character needs to be stored in the result explicitly, to
terminate it.
The description in the manual is updated to deal with these finer
points. The (size_t) -2 behavior (consuming the input bytes) matches
what is specified in ISO C11.
