avoid potential UB when using isprint()

all the ctype.h functions' argument must be representable as an unsigned
char or as EOF, otherwise the behavior is undefined.

1 files changed, 1 insertions, 1 deletions

diff --git a/st.c b/st.c
index 29b7462..7b755eb 100644
--- a/st.c
+++ b/st.c
@@ -377,7 +377,7 @@ static const char base64_digits[] = {
 char
 base64dec_getc(const char **src)
 {
-	while (**src && !isprint(**src))
+	while (**src && !isprint((unsigned char)**src))
 		(*src)++;
 	return **src ? *((*src)++) : '=';  /* emulate padding if string ends */
 }