printf: short-circuit output when argument to %b includes \c

printf wasn't correctly handling \c in an argument to the %b format
specifier.

   printf %bXX OK\\c

returned 'OK\cXX' rather than the expected 'OK'.

function                                             old     new   delta
printf_main                                          886     899     +13

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/printf.c

@@ -131,8 +131,8 @@ static double my_xstrtod(const char *arg)
 	return result;
 }
 
-/* Handles %b */
+/* Handles %b; return 1 if output is to be short-circuited by \c */
-static void print_esc_string(const char *str)
+static int print_esc_string(const char *str)
 {
 	char c;
 	while ((c = *str) != '\0') {
@@ -145,6 +145,9 @@ static void print_esc_string(const char *str)
 					str++;
 				}
 			}
+			else if (*str == 'c') {
+				return 1;
+			}
 			{
 				/* optimization: don't force arg to be on-stack,
 				 * use another variable for that. */
@@ -155,6 +158,8 @@ static void print_esc_string(const char *str)
 		}
 		putchar(c);
 	}
+
+	return 0;
 }
 
 static void print_direc(char *format, unsigned fmt_length,
@@ -280,7 +285,8 @@ static char **print_formatted(char *f, char **argv, int *conv_err)
 			}
 			if (*f == 'b') {
 				if (*argv) {
-					print_esc_string(*argv);
+					if (print_esc_string(*argv))
+						return saved_argv; /* causes main() to exit */
 					++argv;
 				}
 				break;