Audit and replace all ctype.h uses

Something like "char *s = ...; isdigit(s[0]);" triggers undefined
behavior, because char can be signed, and thus s[0] can be a negative
value. The is*() functions require unsigned char _or_ EOF. EOF is a
special value outside of unsigned char range, thus the argument to the
is*() functions can't be a char.

This undefined behavior can actually trigger crashes if the
implementation of these functions e.g. uses lookup tables, which are
then indexed with out-of-range values.

Replace all <ctype.h> uses with our own custom mp_is*() functions added
with misc/ctype.h. As a bonus, these functions are locale-independent.
(Although currently, we _require_ C locale for other reasons.)

1 files changed, 3 insertions, 3 deletions

diff --git a/sub/find_subfiles.c b/sub/find_subfiles.c
index 9313bf379d..ade267cfa6 100644
--- a/sub/find_subfiles.c
+++ b/sub/find_subfiles.c
@@ -1,16 +1,16 @@
 #include <dirent.h>
 #include <string.h>
 #include <stdlib.h>
-#include <ctype.h>
 #include <assert.h>
 
 #include "osdep/io.h"
 
+#include "common/common.h"
 #include "common/global.h"
 #include "common/msg.h"
+#include "misc/ctype.h"
 #include "options/options.h"
 #include "options/path.h"
-#include "common/common.h"
 #include "sub/find_subfiles.h"
 
 static const char *const sub_exts[] = {"utf", "utf8", "utf-8", "idx", "sub", "srt",
@@ -75,7 +75,7 @@ static struct bstr guess_lang_from_filename(struct bstr name)
 
     if (name.start[i] == ')' || name.start[i] == ']')
         i--;
-    while (i >= 0 && isalpha(name.start[i])) {
+    while (i >= 0 && mp_isalpha(name.start[i])) {
         n++;
         if (n > 3)
             return (struct bstr){NULL, 0};