- Generated by
1.9.8
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DBC Framework
DBC parsing and CAN signal decoding framework
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This module provides a minimal but extensible DBC parser and runtime decode foundation for the FrameTap project.
Its purpose is to:
The implementation follows a simple and practical design:
The core library uses C++17 and has no Qt dependency. Qt integration targets the installed Qt 6.8.2, which is the only supported Qt version. Qt Core and Qt Test are used by the regression tests; model tests also link QtGui for graphical metatypes. The optional adapter requires only Qt Core. Live CAN acquisition, trace-file readers, are left to the consuming application. An optional Qt Core model adapter is provided in qt/.
See changelog.md for the release and development history, tests/README.md for test instructions, and generated API documentation for the API reference.
The module is divided into two main paths.
Used for:
Model/ViewPipeline:
Used for:
Pipeline:
This separation is intentional.
The tree is useful for UI, but it is not the main data structure for runtime decoding.
A tree structure is convenient for browsing, but a runtime decoder needs something different:
Because of that, the design uses a dedicated runtime-ready structure:
This avoids forcing UI-oriented structures into a decode role they were not meant for.
| Component | Source files |
|---|---|
| Parsed metadata | core/dbc_database.h, core/frame_info.h, core/signal_info.h |
| Parser and dispatch | core/dbc_parser.*, core/dbc_diagnostic.h, core/dbc_statement_handler.*, core/typefactory.h |
| UI tree | core/tree_node.*, core/dbc_tree_builder.* |
| Runtime database | core/decode_database.h, core/dbc_decode_builder.* |
| Decoder | core/dbc_decoder.* |
| Demo | examples/main.cpp, examples/demo.pro |
| Build integration | core/core.pro, core/core_files.pri, core/core.pri |
Represents one signal as parsed from the DBC file.
Fields:
namestartBitlengthisLittleEndianisSignedfactoroffsetminimummaximumunitreceiverscommentNotes:
receivers is a list because a signal may have more than one receiver ECUfactor and offset define physical conversionPhysical value rule:
Represents one frame as parsed from the DBC file.
Fields:
namecanIdisExtendedpgnhasPgndlctransmittercommentsignalsNotes:
signals is a list of SignalInfoisExtended is determined during CAN ID normalizationpgn is derived using simplified J1939 logic when applicableTop-level parsed DBC container.
Conceptually:
This is the central structure produced by DbcParser.
The UI tree contains three node types:
RootFrameSignalExample hierarchy:
Frame and signal nodes store copies of the corresponding metadata; the root has no metadata payload. The payload types are:
The tree supports browsing through the optional DbcTreeModel adapter.
It is not the primary runtime decode structure.
The decode layer exists so that decoding can be fast and independent from UI concerns.
Instead of searching a tree, the decoder uses a prepared database with direct lookup.
Runtime byte order enum:
IntelMotorolaThis is better for decode code than passing around raw DBC characters.
Numeric type enum:
UnsignedSignedThis is clearer than combining multiple boolean flags during runtime logic.
Represents one runtime-ready signal definition.
Fields:
namestartBitlengthbyteOrdervalueTypefactoroffsetminimummaximumunitreceiverscommentThis structure contains all information required for extracting and converting a signal value from raw frame data.
Represents one runtime-ready frame definition.
Fields:
namecanIdisExtendeddlcpgnhasPgntransmittercommentsignalsThis structure is used directly by the decoder.
Stable identifier for runtime frame matching and application state.
Fields:
canIdisExtendedThis matters because the same numeric identifier must not be confused between standard and extended frames.
Immutable runtime snapshot with a private frame index. Build it with DbcDecodeBuilder::Build(parsed) or construct it from std::vector<DecodeFrame>. Construction rejects duplicate frame keys and duplicate signal names within a frame with std::invalid_argument, including manually supplied metadata.
GetFrames() returns a borrowed const std::vector<DecodeFrame>&.FindFrame(FrameKey) returns std::shared_ptr<const DecodeFrame>.FindSignal(SignalKey) returns std::shared_ptr<const DecodeSignal>.Frame lookup uses a hash index; signal lookup scans the matched frame's signals. Decoding shares the snapshot without copying definitions or allocating ownership objects per signal.
Represents a raw CAN frame to decode.
Fields:
canIdisExtendeddataThis same structure can be used for:
Represents one decoded signal result.
Fields:
definitionkeyrawValuephysicalValuevalidstatusDecodedSignalValue::rawValue is a C++17 std::variant<std::int64_t, std::uint64_t>. For a valid signal, signed definitions produce the int64_t alternative and unsigned definitions produce the uint64_t alternative. Raw values remain exact across their full 64-bit ranges. Check valid before using the physical value. Raw data is also available when status == PhysicalConversionFailed; other invalid results have no decoded numeric data.
Use std::get when the numeric type is known, or std::get_if to handle both:
This replaces the previous int64_t field: consumers that read or print rawValue directly must handle the variant.
Physical conversion uses the active numeric type: physicalValue = static_cast<double>(raw) * factor + offset. physicalValue remains a double and is approximate for large integers. On usual IEEE 754 binary64 implementations, integers are exactly representable through 2^53; above that, some integers round to the same floating-point value. For example, unsigned UINT64_MAX remains exact in rawValue, but converts to approximately 18446744073709551616 in binary64 before scaling. Use rawValue whenever exact integer values are required.
Represents one decoded frame result.
Fields:
definitionkeysignalsvalidstatusvalid means a matching frame definition was found. Check each signal's valid separately: insufficient payload data can leave individual signals invalid even when the frame is valid. An unknown frame returns valid == false, a null definition, its requested key, and an empty signal list.
FrameDecodeStatus summarizes the result:
| Status | Meaning |
|---|---|
UnknownFrame | No definition matches both CAN ID and standard/extended type |
InsufficientPayload | Actual byte count is less than the declared dlc |
SignalErrors | Payload is long enough, but at least one signal failed |
Valid | Payload is long enough and every signal is valid or inactive |
Short-payload status takes precedence over signal errors; inspect each signal's status for the individual cause. valid retains its existing meaning of a matched definition and does not imply status == FrameDecodeStatus::Valid.
Payload policy uses dlc as a byte count, including for CAN FD; it is not the encoded wire DLC. A shorter payload is never padded: all signals whose bytes are available still decode, even if other signals fail. A longer payload is accepted; bytes beyond dlc are ignored. Signal bit layouts must fit the declared dlc, so extra bytes cannot rescue an invalid definition. Empty payloads and zero-byte frame definitions follow the same rules. Results include every signal in definition order, preserving successful values and definition handles on partial failures.
The decoder applies factor and offset; it does not clamp physical values to the declared minimum and maximum. Non-finite conversion results (NaN or positive/ negative infinity), including overflow with finite factor/offset, produce PhysicalConversionFailed. The exact raw value and non-finite physicalValue remain available, while signal valid is false. Non-finite factor/offset in manually constructed definitions follow this same conversion-result check. Physical conversion failure of a selector does not prevent raw branch selection.
DecodedFrameValue::definition and DecodedSignalValue::definition are owning std::shared_ptr<const ...> handles. Each handle retains the immutable runtime snapshot. Definitions remain valid until the last database copy, lookup handle, or decoded result owning that snapshot is released. An independently copied signal result retains its definition even after the parent frame result is removed. Copying or moving results preserves ownership.
Reload by assigning a newly built database. Stored results continue to describe the old DBC, including its units, scaling, comments, and VAL_ descriptions; subsequent decoding uses the new DBC. Removed definitions cannot be found in the new database, but old results safely retain their old definitions. Keeping even one signal handle retains the whole old snapshot; release stored results when that metadata is no longer needed.
GetFrames() is a borrowed view. References, iterators, and raw pointers obtained from it or from a handle's .get() do not retain ownership. Keep an owning handle or an unchanged database copy while using them. Do not retain mutable aliases into a vector moved into the database constructor. The raw string pointer from GetValueDescription() follows the same rule: keep the signal definition handle alive while using the string.
Parsed DbcDatabase/FrameInfo/SignalInfo remain ordinary mutable value containers: borrowed pointers follow standard vector invalidation rules. Builders copy their metadata, so parsed input may be changed or destroyed after building. Tree nodes own metadata copies; the Qt model owns its tree and invalidates model indexes on reset. Runtime handles do not depend on the parsed database or tree. Synchronize replacement of a shared database variable with decoding; immutable snapshots do not make concurrent assignment to the same object safe.
DecodedFrameValue::key is a FrameKey (normalized canId, isExtended), also available through DecodeFrame::GetKey(). DecodedSignalValue::key is a SignalKey (frame key, exact case-sensitive signal name). Both are value types with equality and hashers (FrameKeyHasher, SignalKeyHasher) for application maps and saved selections. Construct the same keys from parsed metadata when needed; do not use addresses or vector positions as identifiers.
Keys stay equal across reloads and reordering when their components stay equal. Frame renaming and changes to units, bit layout, scaling, or descriptions do not change a key. Changing a CAN ID/frame type or renaming a signal produces a new key. The same name in different frames and standard/extended frames with the same numeric CAN ID remain distinct. Keys identify definitions within one logical DBC database; applications combining databases must add their own database ID. A key is not a version identifier: matching keys in different snapshots may have different metadata. Use valid/the definition handle to distinguish a matched result; default keys alone do not indicate successful decoding.
API migration: replace reads of runtime.frames with runtime.GetFrames(). To edit runtime definitions, prepare a vector and construct a new database; frameIndexByKey is now private and built automatically. DbcDecoder::FindFrame and result definition fields now use owning handles instead of raw pointers; definition->name, boolean/null checks, and existing decode calls remain usable. Use .get() only for temporary raw-pointer interoperation with an owner alive.
Main runtime decoder class.
Responsibilities:
Main methods:
FindFrame(...)Decode(...)The current parser supports the following DBC elements:
BO_SG_CM_ BO_CM_ SG_VAL_ signal value descriptionsM / mN multiplexingParseFileWithDiagnostics(path) returns DbcParseResult containing database and diagnostics. Each DbcDiagnostic has severity, code, filePath, lineNumber, and message. Paths preserve the caller's supplied spelling. Lines are one-based physical lines, including blank lines; file-level errors use zero.
| Severity / code | Meaning |
|---|---|
Error / FileOpenError | Input cannot be opened |
Error / FileReadError | Input cannot be read completely |
Error / InvalidStatement | Invalid frame/signal definition, duplicate, or payload violation |
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 / UnsupportedStatement | Extended multiplexing (SG_MUL_VAL_) rejected |
Parsing stops at the first error and returns an empty database, together with any preceding warnings and the error. Deferred VAL_ and multiplexing errors 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_, attributes (BA_, BA_DEF_, defaults and relation forms), 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.
Common VERSION, NS_, BS_, and BU_ headers produce no diagnostics. Single-token symbols inside the NS_ declaration list are quiet regardless of indentation, even when they name unsupported syntax. Frame, signal, bus, and node definitions or a line with arguments end the list. Actual unsupported statements outside that list are reported. Node and bus metadata are not stored. Other comment forms (CM_, CM_ BU_, CM_ EV_) are ignored by the comment handler; comments only attach to already parsed frames/signals. Supported statements currently require one physical line.
ParseFile(path) remains compatible: it returns the database, discards warnings, and throws std::runtime_error on the first error with the existing path:line: format. Use ParseFileWithDiagnostics to see skipped syntax. Resource failures such as allocation errors may still throw.
Example:
Parsed fields:
BO_ definitions require a decimal CAN ID, a nonempty single-token frame name, a colon, a decimal payload length, and a transmitter token. Spaces or tabs may separate fields, and whitespace before the colon is accepted. Additional trailing fields are rejected.
Numeric fields must contain decimal digits only; signs, hexadecimal notation, fractional values, suffixes, and overflow are rejected. CAN IDs may contain the 29-bit identifier plus the optional DBC extended flag (bit 31). Bits 29 and 30 are rejected rather than silently discarded. For compatibility, unflagged IDs above 0x7FF are still treated as extended.
The payload length must fit uint8_t (0..255). This is a storage-range check, not CAN or CAN FD protocol validation; no new 8-byte or 64-byte limit is imposed.
Parsing stops at the first detected error. Exceptions raised while parsing a line are reported as std::runtime_error with the supplied file path and the one-based physical line number, including blank lines:
Frame and signal definitions are validated as described here; comprehensive DBC grammar coverage is still planned. File-open exceptions contain the path but no line number. The structured diagnostic API uses line zero for file-level errors.
Example:
Parsed fields:
SG_ statements are matched completely. Signal names must be nonempty and contain no whitespace. Spaces and tabs are accepted between syntax elements; byte order and signedness remain adjacent (@0+, @0-, @1+, or @1-). A quoted unit (which may be empty) and a nonempty comma-separated receiver list are required. Unexpected trailing fields are rejected.
Start bits must be unsigned decimal integers fitting uint32_t; lengths must be within 1..64 bits. Signs, fractional values, numeric suffixes, and overflow are rejected for these fields. Every signal bit must fit within the frame's declared payload length, using Intel increasing bit positions or Motorola sawtooth traversal. This uses the stored payload length without introducing an additional CAN or CAN FD payload limit.
Factor, offset, minimum, and maximum accept signed decimal numbers, fractions, and scientific notation. The entire numeric token must be valid; hexadecimal numbers, NaN, infinity, conversion overflow, and conversion underflow are rejected. Minimum must not exceed maximum. Zero and negative factors are allowed.
Basic multiplexing markers M and mN are supported as described below. Overlapping signals are rejected unless their branch values differ. Duplicate frame keys and signal names within a frame are rejected.
Invalid signal definitions stop parsing with path:line: description, including when the signal exceeds the declared payload length.
SignalInfo and DecodeSignal contain multiplexing: a MultiplexRole (Unconditional, Selector, or Branch) and an exact uint64_t branch value. Each frame may have one unsigned selector (M); a branch (mN) references that selector implicitly. The selector may appear after its branches. N must contain only decimal digits, fit uint64_t, and fit the selector's bit width. Leading zeros are accepted. A selector without branches is allowed. Signed selectors, missing selectors, multiple selectors, nested/combined markers, and extended SG_MUL_VAL_ statements are rejected with the originating path:line. The dispatcher registers the unsupported statement handler through TypeFactory.
Signal bits may overlap only between branches with different selector values. This validation uses Intel or Motorola bit traversal, including mixed byte orders. It also rejects overlapping unconditional signals. Metadata survives the runtime and tree builders; the optional Qt adapter does not add multiplexing roles yet.
The shared decoder extracts the selector before processing branches, compares its raw unsigned value, and leaves result order equal to definition order. Factor, offset, and VAL_ descriptions do not influence branch selection. Unconditional signals continue to decode. An unmapped selector value leaves all branches inactive.
Each result has SignalDecodeStatus status:
| Status | Meaning |
|---|---|
Valid | Raw and physical values are available; valid == true |
Inactive | Selector is available and chooses another branch |
SelectorUnavailable | Branch activation is unknown because selector bytes are missing |
InsufficientPayload | Selected or unconditional signal bytes are missing |
InvalidDefinition | Invalid length, byte order, numeric type, multiplexing role, layout outside declared DLC, or missing/invalid selector in manually built runtime metadata |
PhysicalConversionFailed | Raw value is available, but the converted physical value is NaN or infinity |
All statuses except Valid have valid == false and GetValueDescription() returns nullptr. PhysicalConversionFailed preserves extracted raw data and the non-finite conversion result; other invalid statuses have no decoded numeric data. Check status to distinguish inactive branches from errors. Consumers constructing runtime metadata manually must obey the same non-overlap rules as the parser. Extended and nested multiplexing are outside this stage and are explicitly rejected, rather than silently decoded as unconditional signals.
Frame comment example:
Signal comment example:
Stored in:
The parser normalizes frame identifiers.
Common DBC behavior:
The parser therefore stores:
canIdisExtended flagThis is important both for correct lookup and for future interoperability with live CAN APIs.
PGN is derived only when the frame is treated as extended.
The current logic is simplified J1939 extraction:
pfpsdpThis is enough for a practical start but should not be treated as full J1939 validation.
Typical runtime decode flow:
The decoder currently has separate extraction paths:
ExtractIntel(...)ExtractMotorola(...)This is important because byte order is not just metadata once decoding starts.
Intel and Motorola require different bit extraction logic.
This is one of the main reasons why the runtime decode layer should be explicit and prepared in advance.
Include the public headers from the core/ include directory supplied by core/core.pri:
A key design goal is that the same decoder should work for both:
That means this architecture supports:
This avoids duplicating decode logic in two separate parts of the application.
This module is meant to support at least the following FrameTap workflows:
Example combined workflow:
The tree exists for browsing.
However, runtime decode should not rely on tree traversal because that would introduce unnecessary coupling and inefficiency.
A runtime decoder needs:
That is why DecodeDatabase is a separate layer.
DbcParser owns file reading, trimming, line numbers, and error reporting. Each ParseFile() call creates a fresh DbcParseContext and a DbcStatementDispatcher. The context contains the parsed database and current frame; handlers receive it by reference and retain no parsing state.
The dispatcher uses TypeFactory<std::string, DbcStatementHandler> to create registered handlers once per parsing session, then reuses them for all matching lines:
BO_ → DbcFrameHandlerSG_ → DbcSignalHandlerCM_ → DbcCommentHandlerVAL_ → DbcValueDescriptionHandlerSG_MUL_VAL_ → DbcUnsupportedMultiplexingHandlerVERSION, NS_, BS_, BU_ → DbcHeaderHandler (also accepts attached colons)Grammar implementations live in core/dbc_statement_handler.cpp; their interface, context, and dispatcher live in core/dbc_statement_handler.h. core/typefactory.h provides the generic registry and object creation.
To add a construct, implement a default-constructible handler deriving from DbcStatementHandler with:
Register it in the dispatcher constructor:
Registration creates one handler; replacing a registration replaces that instance. 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.
This factory handles statements inside DBC files. A separate format-level factory can be introduced when another file format is implemented. The decoder and database builders remain independent of statement dispatch.
Signal descriptions attach text to exact raw integer values:
Each statement must occupy one physical line, contain at least one integer/text pair, and end with a semicolon. Spaces and tabs are accepted between fields; descriptions may contain whitespace, semicolons, and empty text. Inside quoted text, \"</tt> and <tt>\\\\</tt> represent a quote and a backslash; other escapes are rejected.
Keys are decimal integers in <tt>INT64_MIN..UINT64_MAX</tt>, with an optional minus
sign; plus signs, fractions, hexadecimal numbers, exponents, and overflow are
rejected. Keys never pass through <tt>double</tt>.
<tt>VAL_</tt> may appear before or after its frame and signal declarations. References
are resolved after reading the file using the same CAN ID normalization as
<tt>BO_</tt>, including bit 31 for extended identifiers. Standard and extended frames
with the same normalized ID remain distinct. Missing or ambiguous references,
malformed statements, and duplicate integer keys produce <tt>path:line: description</tt>
errors at the originating <tt>VAL_</tt> line. Distinct keys from multiple statements
are merged; <tt>0</tt>, <tt>00</tt>, and <tt>-0</tt> are the same key. Keys need not fit the referenced
signal's bit width or signedness; unreachable keys simply cannot match a decode.
Mappings are available as <tt>SignalInfo::valueDescriptions</tt> and
<tt>DecodeSignal::valueDescriptions</tt>, and survive both database builders, including
<tt>TreeNode::GetSignal()</tt>. Consumers can look up a decoded result directly:
@icode{cpp}
const DecodedSignalValue &value = decodedFrame.signals.at(0);
if (const std::string *description = value.GetValueDescription()) {
std::cout << *description;
}
@endicode
<tt>GetValueDescription()</tt> uses the exact raw integer before factor/offset scaling.
It returns <tt>nullptr</tt> for an invalid decode or an unknown value; numeric decoding
and <tt>physicalValue</tt> are unchanged. A mapped empty string returns a non-null
pointer. The pointer belongs to the signal definition and stays valid while that
definition remains alive. A decoded signal owns its immutable definition across reload.
For metadata or standalone raw values, use
<tt>FindValueDescription(signal.valueDescriptions, rawValue)</tt>, where <tt>rawValue</tt> is
<tt>RawSignalValue</tt> (<tt>std::variant\<std::int64_t, std::uint64_t\></tt>). The helper matches
nonnegative signed and unsigned values identically and keeps negative values
distinct from large unsigned values. Stored keys use negative <tt>int64_t</tt> and
nonnegative <tt>uint64_t</tt>; when constructing mappings manually, normalize keys
with <tt>NormalizeValueKey()</tt> before insertion.
Named <tt>VAL_TABLE_</tt> tables, environment-variable mappings, multiline statements,
are outside this implementation; the optional Qt adapter exposes signal mappings.
<hr>
@section autotoc_md117 Current Limitations
This is still a minimal implementation.
Not supported yet:
- extended and nested multiplexing (<tt>SG_MUL_VAL_</tt>, <tt>mNM</tt>)
- named <tt>VAL_TABLE_</tt> tables and environment-variable value descriptions
- <tt>BA_</tt> attributes
- <tt>BA_DEF_</tt> definitions and attribute defaults
- <tt>SIG_VALTYPE_</tt> floating-point signal types
- signal types/references (<tt>SGTYPE_</tt>, <tt>SIG_TYPE_REF_</tt>) and environment variables
- advanced comment handling
- full DBC grammar coverage
- full J1939 validation
- extensive edge-case handling for unusual DBC formatting
Additional behavior to account for:
- unregistered DBC keywords are skipped with warnings in the diagnostic API
- an <tt>SG_</tt> statement before the first frame is rejected
- duplicate frame keys (normalized CAN ID and frame type) and repeated signal
names within a frame are rejected at their definition lines; manually created
databases are also checked for ambiguous <tt>VAL_</tt> references during resolution
- payload lengths are checked against storage bounds (<tt>0..255</tt>), rather than
CAN or CAN FD protocol limits
- comment handling is limited to the supported forms and already parsed targets
Motorola extraction uses DBC sawtooth numbering: a start bit of 7 traverses
<tt>7..0, 15..8, 23..16</tt>. Regression tests cover aligned and unaligned signals,
byte boundaries, and 64-bit values.
<hr>
@section autotoc_md119 Recommended Next Steps
A practical development order would be:
@subsection autotoc_md120 Stage 1 - already implemented
- <tt>BO_</tt>
- <tt>SG_</tt>
- <tt>CM_</tt>
- <tt>VAL_</tt> signal value descriptions
- normalized CAN ID
- <tt>isExtended</tt>
- transmitter
- receivers
- comments
- tree representation
- runtime decode database
- runtime decoder
@subsection autotoc_md121 Stage 2
Recommended additions:
- selective decoding of only chosen signals
@subsection autotoc_md122 Stage 3
Recommended additions:
- basic multiplexing (implemented)
- attribute parsing
- richer J1939 support
- CSV export of decoded traces
- optimized filtering and signal selection
@subsection autotoc_md123 Stage 4
Advanced functionality:
- live plot integration
- signal subscriptions
- per-signal trace decode pipelines
- decoder-assisted export formats
<hr>
@section autotoc_md125 Build Integration
The repository supplies qmake projects. A C++17 compiler is required; the root
build also requires Qt Core and Qt Test development packages. Other build
systems can compile the sources listed in <tt>core/core_files.pri</tt>; no CMake
configuration is currently provided.
Qt-dependent qmake targets share <tt>qt/qt_version.pri</tt>, which rejects Qt versions
other than 6.8.2. The core library remains independent of Qt libraries.
Open <tt>dbc.pro</tt> in Qt Creator to see two subprojects: <tt>core</tt> and <tt>tests</tt>.
<tt>core/core.pro</tt> builds the C++17 static library <tt>dbc_core</tt> without a Qt dependency.
<tt>tests/tests.pro</tt> builds the QtTest executable <tt>dbc_tests</tt> and links that library.
The root project declares <tt>tests.depends = core</tt> for parallel builds.
Build out of source with Qt 6.8.2:
@icode{sh}
mkdir build
cd build
qmake6 ../dbc.pro
make -j
make check
@endicode
<tt>core/core_files.pri</tt> lists the library sources and headers.
Consumers include <tt>core/core.pri</tt> for include paths and library linkage; the test
source lists live in <tt>tests/parser_tests.pri</tt> and <tt>tests/decoder_tests.pri</tt>.
When building a consumer separately, pass
<tt>DBC_CORE_BUILD_DIR=/absolute/path/to/build/core</tt> to qmake.
@subsection autotoc_md126 Build core without Qt libraries
From the repository root:
@icode{sh}
mkdir -p build/core
cd build/core
qmake6 ../../core/core.pro
make -j
@endicode
qmake is still the build tool; this target does not link Qt libraries.
@subsection autotoc_md127 Optional Qt model adapter
The adapter and its <tt>QAbstractItemModelTester</tt> suite use Qt 6.8.2.
The adapter itself links only Qt Core.
The model test executable additionally links QtGui and uses QGuiApplication so
QAbstractItemModelTester can resolve graphical metatypes such as QPixmap. It
defaults to the <tt>offscreen</tt> platform when <tt>QT_QPA_PLATFORM</tt> is unset or empty;
no display server is required. An explicit platform setting is preserved.
Enable its library and focused QtTest suite:
@icode{sh}
mkdir -p build-qt
cd build-qt
qmake6 ../dbc.pro CONFIG+=dbc_qt
make -j
make check
@endicode
Consumers include <tt>qt/qt.pri</tt> instead of <tt>core/core.pri</tt>, and set
<tt>DBC_CORE_BUILD_DIR</tt> and <tt>DBC_QT_BUILD_DIR</tt> to the corresponding library build
directories when building separately. A widget application also needs <tt>QT += widgets</tt>. The adapter integration enables
<tt>no_keywords</tt>, because core metadata has a <tt>signals</tt> member; use <tt>Q_SIGNALS</tt>,
<tt>Q_SLOTS</tt>, and <tt>Q_EMIT</tt> in consuming Qt classes.
@icode{cpp}
#include "dbc_parser.h"
#include "dbc_tree_builder.h"
#include "dbc_tree_model.h"
#include <QTreeView>
// Run after constructing QApplication; view owns the model through QObject.
QTreeView view;
DbcTreeModel *model = new DbcTreeModel(&view);
model->SetTree(DbcTreeBuilder().Build(DbcParser().ParseFile("example.dbc")));
view.setModel(model);
view.expandAll();
view.show();
// On reload, pass a newly built tree to SetTree(); to clear:
// model->SetTree(nullptr);
@endicode
The root is invisible: frames are top-level rows, signals are their children.
Only column zero has children. <tt>parent()</tt> always returns column zero.
The model takes exclusive ownership of the tree; do not retain mutable aliases.
Metadata is copied by the tree builder, so the parsed database may be destroyed.
<tt>TreeNode::GetParent()</tt> is non-owning and <tt>GetRow()</tt> gives the zero-based sibling
position (zero for a detached node/root). Nodes cannot be copied or moved;
transferring their <tt>unique_ptr</tt> ownership preserves addresses and navigation.
Call <tt>SetTree()</tt> on the model's thread. It accepts a detached Root or nullptr,
uses <tt>beginResetModel()</tt>/<tt>endResetModel()</tt>, and destroys the previous tree during
reset. All ordinary QModelIndex values expire on reset and must not be reused;
QPersistentModelIndex values are invalidated by Qt. Destroying the model also
invalidates indexes. Invalid and foreign indexes return no data/flags/children.
Valid items are enabled and selectable, with no editing support.
<table class="markdownTable">
<tr class="markdownTableHead"> <th class="markdownTableHeadNone"> Column (zero-based enum)
Frame display
Signal display
0 Name
Name
Name
1 CanId
Normalized hexadecimal ID
Empty
2 PayloadLength
Bytes
Empty
3 StartBit
Empty
DBC start bit
4 BitLength
Empty
Bit count
5 ByteOrder
Empty
Intel / Motorola
6 Signed
Empty
Signed / Unsigned
7 Unit
Empty
Unit
8 Comment
Comment
Comment
Horizontal DisplayRole headers describe these columns; other header requests return invalid QVariant. ToolTipRole returns the comment on every column. Custom roles also apply on every column; inapplicable roles return invalid QVariant:
| Role | Node types | QVariant content |
|---|---|---|
NodeTypeRole | Frame, signal | int corresponding to NodeType |
CanIdRole, PayloadLengthRole, ExtendedRole | Frame | uint, int, bool |
StartBitRole, BitLengthRole | Signal | uint |
LittleEndianRole, SignedRole | Signal | bool |
UnitRole | Signal | QString |
CommentRole | Frame, signal | QString |
ValueDescriptionsRole | Signal | QVariantList of QVariantMap entries |
Each value-description entry contains value (qlonglong for negative keys, qulonglong for nonnegative keys) and description (QString). This preserves the full signed/unsigned 64-bit range without converting through double. An unmapped signal returns an empty list. Data comes from SignalInfo::valueDescriptions. Unsupported roles return invalid QVariant.
From the repository root, use only a C++17 compiler:
After building core, run these commands from the repository root:
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.
With Doxygen installed, run from the repository root:
Open docs/html/index.html to view the generated reference.
See tests/README.md for QtTest build and execution commands. Tests cover frame validation and error locations, Intel and Motorola extraction, signal syntax and payload bounds, VAL_ syntax and reference validation, raw description lookup and preservation through both builders, statement dispatch, signed and unsigned 64-bit boundaries, physical conversion, numeric output, and invalid signal payloads.
Coverage instrumentation is separate from the QtTest suite named CoverageTest: that suite runs extra regression checks, but coverage counters require a specially instrumented build. Use a separate build directory for each coverage tool.
Install the build and report tools:
GCC supplies gcov; the lcov package supplies lcov and genhtml. Use the gcov version matching the GCC used by the selected Qt Creator kit. These instructions use GCC and Qt 6.8.2.
From the repository root, create a fresh coverage build. --coverage must be passed to both compilation and linking; Debug avoids optimization that can make source-level results harder to interpret. -fprofile-abs-path makes source paths in the coverage data independent of the compilation working directory.
Open build-coverage/html/index.html in a browser. The report includes the library's core/ and qt/ sources and instantiated header code; test sources, generated moc files, and Qt/STL headers are excluded. Click a filename to inspect execution counts, uncovered lines, and branch outcomes. Branch coverage is a separate metric: executing a line does not necessarily exercise every outcome. C++ branch data can also include compiler-generated exception paths.
For another run with unchanged sources, repeat the reset, test execution, capture, merge, and HTML generation steps. After changing sources or compiler flags, rebuild and regenerate baseline.info before measuring again. A fresh build directory avoids mixing old profiling data with a different build.
An initial measurement with GCC 14.2 and Qt 6.8.2 on 2026-10-07, including both QtTest executables and the standalone tree test, yielded 97.8% line coverage (724/740) and 70.7% branch coverage (833/1178). These are a snapshot, not fixed expected values for later changes or other toolchains.
After adding direct comment-handler and ambiguous VAL_ reference tests, the same configuration measured 98.4% line coverage (728/740) and 71.4% branch coverage (841/1178).
See GCC instrumentation options and the LCOV project documentation.
dbc.pro and select a GCC kit with Qt 6.8.2.build-coverage.Expand the qmake build step and add these Additional arguments:
dbc_tests and dbc_model_tests must run to include coverage from the core and optional model adapter.DBC_SOURCE_DIR to the absolute repository path if using a new terminal. make check runs both QtTest executables; the standalone tree executable must be run separately.html/index.html in a browser. This workflow produces HTML reports; it does not require a licensed coverage toolchain.The local dbc.pro.user stores machine-specific kit IDs and build/run settings. It is ignored by Git (*.user) and should not be committed or copied between machines. Recreate the configurations below through the UI when setting up a new checkout. The Qt4ProjectManager identifiers inside .user are historical Qt Creator setting names; the project still requires Qt 6.8.2.
The local configuration set uses these independent build directories:
| Configuration | Build directory example | Purpose |
|---|---|---|
| Debug | /tmp/build/dbc/Desktop-Debug | Core library and parser/decoder/coverage regression tests |
| Release | /tmp/build/dbc/Desktop-Release | The same targets with release settings |
| Profile | /tmp/build/dbc/Desktop-Profile | Existing Qt Creator profiling configuration; not code coverage |
| Debug Qt Models | /tmp/build/dbc/Desktop-Debug-Qt-Models | Debug targets plus optional adapter and model tests |
| Release Qt Models | /tmp/build/dbc/Desktop-Release-Qt-Models | Release targets plus optional adapter and model tests |
| Debug Qt Models Strict | /tmp/build/dbc/Desktop-Debug-Qt-Models-Strict | Model build with QT_FATAL_WARNINGS=1 for builds and runs |
| Coverage | /tmp/build/dbc/Desktop-Coverage | Instrumented core/model build, test execution, and LCOV HTML report |
| Core Only | /tmp/build/dbc/Desktop-Core-Only | The Qt-free core static library |
| Tree Tests | /tmp/build/dbc/Desktop-Tree-Tests | Standalone C++17 tree test without Qt |
| Demo | /tmp/build/dbc/Desktop-Demo | Core library and command-line demo |
The temporary paths are examples; choose permanent build directories if desired. Do not share a build directory between these configurations.
To add the ordinary qmake configurations:
dbc.pro with a GCC/Qt 6.8.2 kit.CONFIG+=dbc_qt to the qmake step's Additional arguments.QT_FATAL_WARNINGS=1. Run configurations should use the build environment.Clone Debug Qt Models as Coverage. In qmake Additional arguments, use:
| Field | Value |
|---|---|
| Command | /bin/sh |
| Arguments | "%{sourceDir}/tests/coverage_report.sh" "%{sourceDir}" "%{buildDir}" |
| Working directory | %{buildDir} |
This script compiles the standalone tree test, resets counters, runs both QtTest executables and the tree test, and generates %{buildDir}/html/index.html. It stops if any test fails. Therefore building Coverage also executes tests. lcov and genhtml must be installed. Use this configuration with the GCC kit; gcov and the compiler used for the standalone test must match that kit.
dbc_tests; model configurations also expose dbc_model_tests.Qt Creator expands %{sourceDir} and %{buildDir} in custom steps to the source and active build directories. Use the field's variable chooser if needed.
For the three independent builds, clone Debug, assign the name and build directory from the table, and replace its qmake/Make build steps with the custom process steps below. These steps are local IDE settings and do not change dbc.pro. Give each step a descriptive name and retain the listed order.
For Core Only:
| Command | Arguments | Working directory |
|---|---|---|
/usr/bin/mkdir | -p "%{buildDir}" | %{sourceDir} |
/usr/bin/qmake6 | "%{sourceDir}/core/core.pro" CONFIG+=debug CONFIG-=release | %{buildDir} |
/usr/bin/make | -j4 | %{buildDir} |
Keep a clean step with make clean in %{buildDir}. Core Only creates a static library, so there is no executable to run.
For Tree Tests:
/usr/bin/mkdir, arguments -p "%{buildDir}", and working directory %{sourceDir}.Add a custom step with command /usr/bin/c++, working directory %{buildDir}, and these arguments:
For Demo:
| Command | Arguments | Working directory |
|---|---|---|
/usr/bin/mkdir | -p "%{buildDir}/core" "%{buildDir}/examples" | %{sourceDir} |
/usr/bin/qmake6 | "%{sourceDir}/core/core.pro" CONFIG+=debug CONFIG-=release | %{buildDir}/core |
/usr/bin/make | -j4 | %{buildDir}/core |
/usr/bin/qmake6 | "%{sourceDir}/examples/demo.pro" "DBC_CORE_BUILD_DIR=%{buildDir}/core" CONFIG+=debug CONFIG-=release | %{buildDir}/examples |
/usr/bin/make | -j4 | %{buildDir}/examples |
Replace the default clean step with two custom steps: /usr/bin/make with arguments clean, first in %{buildDir}/examples, then in %{buildDir}/core.
To configure execution and switch variants:
dbc_tests for ordinary builds or dbc_model_tests for model builds./usr/bin/make, arguments check, and working directory %{buildDir}. Use it with an ordinary or model qmake configuration. Coverage already runs every test in its final build step.%{buildDir}/tree_node_tests, working directory %{buildDir}, and no arguments.%{buildDir}/examples/dbc_demo, working directory %{buildDir}/examples. Set Command line arguments to the quoted absolute path of your DBC file./usr/bin/xdg-open, arguments "%{buildDir}/html/index.html", working directory %{buildDir}. Running it opens the generated report in the default browser..user was edited externally, close and reopen the project so Qt Creator reads the new settings. Do not edit it while the project is open, because Qt Creator can overwrite external changes when saving its session.See Qt Creator's build configuration guide and run configuration guide.
1.9.8