Silence compiler warnings about array subscripts of type 'char'

Cygwin GCC complains about code like isprint(c), where c is of type char.
The isX() and toX() functions/macros (ISO C allows either) all accept an
int, whose value should be either that of an unsigned char, or the
special value EOF (== -1).
So cast to unsigned char each argument to isprint, tolower, etc.

Silences several warnings of the form:

gpsutils.c: In function 'safe_atof':
gpsutils.c:90:5: warning: array subscript has type 'char'
[-Wchar-subscripts]
      while (isspace(*p)) {
      ^
gpsutils.c:188:2: warning: array subscript has type 'char'
[-Wchar-subscripts]
   while (isdigit(*p)) {
   ^

1 files changed, 1 insertions, 1 deletions

diff --git a/hex.c b/hex.c
index ac1705f3..635bd53a 100644
--- a/hex.c
+++ b/hex.c
@@ -17,7 +17,7 @@ const char /*@ observer @*/ *gpsd_packetdump(char *scbuf, size_t scbuflen,
 
     assert(binbuf != NULL);
     for (cp = binbuf; cp < binbuf + binbuflen; cp++)
-	if (!isprint(*cp) && !isspace(*cp))
+	if (!isprint((unsigned char) *cp) && !isspace((unsigned char) *cp))
 	    printable = false;
     if (printable)
 	return binbuf;