From a0da280f6451c4ed20b711edb84dc3d258823e20 Mon Sep 17 00:00:00 2001
From: Kosma Moczek <kosma@kosma.pl>
Date: Fri, 3 Jun 2022 01:40:30 +0200
Subject: [PATCH] add test_minmea_parse_vtg3 (fixes #57)

---
 minmea.c | 17 ++++++++++-------
 tests.c  | 22 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/minmea.c b/minmea.c
index 89ef76b..e9361cc 100644
--- a/minmea.c
+++ b/minmea.c
@@ -594,7 +594,7 @@ bool minmea_parse_vtg(struct minmea_sentence_vtg *frame, const char *sentence)
     char type[6];
     char c_true, c_magnetic, c_knots, c_kph, c_faa_mode;
 
-    if (!minmea_scan(sentence, "tfcfcfcfc;c",
+    if (!minmea_scan(sentence, "t;fcfcfcfcc",
             type,
             &frame->true_track_degrees,
             &c_true,
@@ -608,12 +608,15 @@ bool minmea_parse_vtg(struct minmea_sentence_vtg *frame, const char *sentence)
         return false;
     if (strcmp(type+2, "VTG"))
         return false;
-    // check chars
-    if (c_true != 'T' ||
-        c_magnetic != 'M' ||
-        c_knots != 'N' ||
-        c_kph != 'K')
-        return false;
+    // values are only valid with the accompanying characters
+    if (c_true != 'T')
+        frame->true_track_degrees.scale = 0;
+    if (c_magnetic != 'M')
+        frame->magnetic_track_degrees.scale = 0;
+    if (c_knots != 'N')
+        frame->speed_knots.scale = 0;
+    if (c_kph != 'K')
+        frame->speed_kph.scale = 0;
     frame->faa_mode = (enum minmea_faa_mode)c_faa_mode;
 
     return true;
diff --git a/tests.c b/tests.c
index 1a63380..90a935e 100644
--- a/tests.c
+++ b/tests.c
@@ -895,6 +895,27 @@ START_TEST(test_minmea_parse_vtg2)
 }
 END_TEST
 
+START_TEST(test_minmea_parse_vtg3)
+{
+    // https://github.com/kosma/minmea/issues/57
+    const char *sentence = "$GNVTG,,,,,,,,,N*2E";
+    // clear structs before initialization to enable use of memcmp()
+    struct minmea_sentence_vtg frame = {};
+    struct minmea_sentence_vtg expected = {};
+    expected = (struct minmea_sentence_vtg){
+        .true_track_degrees = { 0, 0 },
+        .magnetic_track_degrees = { 0, 0 },
+        .speed_knots = { 0, 0 },
+        .speed_kph = { 0, 0 },
+        .faa_mode = MINMEA_FAA_MODE_NOT_VALID,
+    };
+    ck_assert(minmea_check(sentence, false) == true);
+    ck_assert(minmea_check(sentence, true) == true);
+    ck_assert(minmea_parse_vtg(&frame, sentence) == true);
+    ck_assert(!memcmp(&frame, &expected, sizeof(frame)));
+}
+END_TEST
+
 START_TEST(test_minmea_parse_zda1)
 {
     const char *sentence = "$GPZDA,160012.71,11,03,2004,-1,00*7D";
@@ -1133,6 +1154,7 @@ static Suite *minmea_suite(void)
     tcase_add_test(tc_parse, test_minmea_parse_gsv5);
     tcase_add_test(tc_parse, test_minmea_parse_vtg1);
     tcase_add_test(tc_parse, test_minmea_parse_vtg2);
+    tcase_add_test(tc_parse, test_minmea_parse_vtg3);
     tcase_add_test(tc_parse, test_minmea_parse_zda1);
     suite_add_tcase(s, tc_parse);