keep the exponent when trimming zeroes with JSON_C_TO_STRING_NOZERO

json_object.c

@@ -1328,15 +1328,18 @@ static int json_object_double_to_json_string_format(struct json_object *jso, str
 		{
 			/* last useful digit, always keep 1 zero */
 			p++;
-			for (q = p; *q; q++)
+			for (q = p; is_plain_digit(*q); q++)
 			{
 				if (*q != '0')
 					p = q;
 			}
-			/* drop trailing zeroes */
-			if (*p != 0)
-				*(++p) = 0;
-			size = p - buf;
+			/* drop trailing zeroes, keeping any exponent after them */
+			if (is_plain_digit(*p))
+			{
+				p++;
+				memmove(p, q, strlen(q) + 1);
+			}
+			size = (int)strlen(buf);
 		}
 	}
 	// although unlikely, snprintf can fail

tests/test_double_serializer.c

@@ -41,6 +41,18 @@ int main(int argc, char **argv)
 	json_object_set_serializer(obj, json_object_double_to_json_string, data, NULL);
 	printf("obj.to_string(reset)=%s\n", json_object_to_json_string_ext(obj, 4));
 
+	json_object_put(obj);
+	/* NOZERO must only trim the fraction, never the exponent */
+	obj = json_object_new_double(1.5e20);
+	printf("obj(1.5e20).to_string(nozero)=%s\n",
+	       json_object_to_json_string_ext(obj, JSON_C_TO_STRING_NOZERO));
+	json_object_put(obj);
+	obj = json_object_new_double(1.5e20);
+	char data_e[] = "%.3e";
+	json_object_set_serializer(obj, json_object_double_to_json_string, data_e, NULL);
+	printf("obj(1.5e20).to_string(%%.3e,nozero)=%s\n",
+	       json_object_to_json_string_ext(obj, JSON_C_TO_STRING_NOZERO));
+
 	json_object_put(obj);
 	obj = json_object_new_double(0.52381);
 

tests/test_double_serializer.expected

@@ -8,6 +8,8 @@ Test reset serializer:
 obj.to_string(reset)=0.5
 Test no zero reset serializer:
 obj.to_string(reset)=3.1415000000000002
+obj(1.5e20).to_string(nozero)=1.5e+20
+obj(1.5e20).to_string(%.3e,nozero)=1.5e+20
 obj.to_string(default format)=0.52381
 obj.to_string(with global format)=x0.524y
 obj.to_string(with thread format)=T0.52X