msvcrt: Implement %C format for strftime.

dlls/msvcrt/tests/time.c

@@ -609,6 +609,11 @@ static void test_strftime(void)
     ok(gmt_tm != NULL, "gmtime failed\n");
 
     errno = 0xdeadbeef;
+    retA = p_strftime(bufA, 256, "%C", gmt_tm);
+    ok(retA == 0, "expected 0, got %ld\n", retA);
+    ok(errno==EINVAL || broken(errno==0xdeadbeef), "errno = %d\n", errno);
+
+    errno = 0xdeadbeef;
     retA = p_strftime(bufA, 256, "%D", gmt_tm);
     ok(retA == 0, "expected 0, got %ld\n", retA);
     ok(errno==EINVAL || broken(errno==0xdeadbeef), "errno = %d\n", errno);

dlls/msvcrt/time.c

@@ -1153,6 +1153,13 @@ static MSVCRT_size_t strftime_helper(char *str, MSVCRT_size_t max, const char *f
             if(!strftime_str(str, &ret, max, time_data->str.names.mon[mstm->tm_mon]))
                 return 0;
             break;
+#if _MSVCR_VER>=140
+        case 'C':
+            tmp = (1900+mstm->tm_year)/100;
+            if(!strftime_int(str, &ret, max, tmp, alternate ? 0 : 2, 0, 99))
+                return 0;
+            break;
+#endif
         case 'd':
             if(!strftime_int(str, &ret, max, mstm->tm_mday, alternate ? 0 : 2, 0, 31))
                 return 0;

dlls/ucrtbase/tests/misc.c

@@ -895,6 +895,10 @@ static void test_strftime(void)
     char bufA[256];
     size_t retA;
 
+    retA = p_strftime(bufA, sizeof(bufA), "%C", &epoch);
+    ok(retA == 2, "expected 2, got %d\n", (int)retA);
+    ok(!strcmp(bufA, "19"), "got %s\n", bufA);
+
     retA = p_strftime(bufA, sizeof(bufA), "%D", &epoch);
     ok(retA == 8, "expected 8, got %d\n", (int)retA);
     ok(!strcmp(bufA, "01/01/70"), "got %s\n", bufA);