tried to parse string functions using constexpr in C++

F0:F030,F042,F072/usbcan_gpio/hashparser.h

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+/*
+ * This file is part of the usbcangpio project.
+ * Copyright 2026 Edward V. Emelianov <edward.emelianoff@gmail.com>.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+// error codes for answer message
+typedef enum{
+    ERR_OK,         // all OK
+    ERR_BADPAR,     // wrong parameter
+    ERR_BADVAL,     // wrong value (for setter)
+    ERR_WRONGLEN,   // wrong message length
+    ERR_CANTRUN,    // can't run given command due to bad parameters or other
+    ERR_AMOUNT      // amount of error codes or "send nothing"
+} errcodes_t;
+
+// maximal length of command (without trailing zero)
+#define CMD_MAXLEN  (15)
+
+void chk(char *str);