Closes #33

README.md

@@ -639,6 +639,7 @@ if (!result.HasErrors()) {
 | `Error` / `InvalidValueDescription` | Invalid `VAL_` syntax, duplicate value, or unresolved reference |
 | `Error` / `InvalidMultiplexing` | Selector, branch range, or signal overlap validation failed |
 | `Warning` / `UnsupportedStatement` | Unregistered statement skipped; decoding or metadata may be incomplete |
+| `Error` / `UnsupportedSignalType` | `SIG_VALTYPE_` declaration rejected to prevent incorrect integer decoding |
 | `Error` / `InvalidMultiplexing` | Invalid `SG_MUL_VAL_` syntax, references, ranges, or cycles |
 
 Parsing stops at the first error and returns an empty database, together with
@@ -646,11 +647,20 @@ any preceding warnings and the error. Deferred comment, `VAL_`, and multiplexing
 retain their original source lines. Invalid signal markers use `InvalidStatement`.
 `HasErrors()` checks severity; warnings alone do not make a parse fail.
 
-Unknown statements are reported conservatively, including `SIG_VALTYPE_`,
-attribute relation forms (`BA_REL_`, `BA_DEF_REL_`), signal types/references,
-environment variables, named `VAL_TABLE_` tables, and vendor extensions. For
-example, ignoring `SIG_VALTYPE_` may decode a floating-point signal as an integer.
-The parser does not implement the warned features; consumers should review warnings.
+All `SIG_VALTYPE_` declarations are rejected with `Error / UnsupportedSignalType`.
+This includes float32 (type 1), float64 (type 2), type 0, unknown types, and
+malformed declarations: the operator itself is not implemented. `ParseFile()`
+throws a source-located error; `ParseFileWithDiagnostics()` returns an empty
+database with the error and any preceding warnings. There is no permissive mode.
+This prevents IEEE 754 payload bits from being interpreted as a valid integer
+signal. Integer signals defined with `SG_` without this operator are unchanged.
+A bare `SIG_VALTYPE_` symbol inside an `NS_` symbol list remains quiet header
+metadata, rather than a value-type declaration.
+
+Other unknown statements are reported conservatively, including attribute
+relation forms (`BA_REL_`, `BA_DEF_REL_`), signal types/references, environment
+variables, named `VAL_TABLE_` tables, and vendor extensions. The parser does not
+implement the warned features; consumers should review warnings.
 
 ### Attributes and frame metadata
 
@@ -1205,7 +1215,9 @@ Registration creates one handler; replacing a registration replaces that instanc
 Register during initialization before dispatching. A line is routed using its
 full first whitespace-delimited keyword, so `BO_TX_BU_` cannot match `BO_`.
 Unregistered keywords produce `UnsupportedStatement` warnings through
-`ParseFileWithDiagnostics`. `SG_` and `CM_` accept spaces and tabs after their keywords.
+`ParseFileWithDiagnostics`. A registered rejection handler for `SIG_VALTYPE_`
+produces `UnsupportedSignalType` errors instead of skipping the declaration.
+`SG_` and `CM_` accept spaces and tabs after their keywords.
 
 This factory handles statements inside DBC files. A separate format-level
 factory can be introduced when another file format is implemented. The decoder
@@ -1280,7 +1292,7 @@ Not supported yet:
 - multiple parent selectors for one signal
 - named `VAL_TABLE_` tables and environment-variable value descriptions
 - attribute relation forms (`BA_REL_`, `BA_DEF_REL_`)
-- `SIG_VALTYPE_` floating-point signal types
+- explicit `SIG_VALTYPE_` signal value types (declarations are rejected with an error)
 - signal types/references (`SGTYPE_`, `SIG_TYPE_REF_`) and environment variables
 - advanced comment handling
 - full DBC grammar coverage
@@ -1523,6 +1535,10 @@ The demo prints the parsed tree and decodes eight zero bytes using the first
 frame definition. Replace that sample payload in `examples/main.cpp` to feed
 live CAN data or trace records.
 
+The demo prints all parser diagnostics, including severity and source location,
+and exits with code 2 before building or decoding when parsing reports an error.
+Warnings remain visible when parsing succeeds.
+
 ### Generate API documentation
 
 With Doxygen installed, run from the repository root: