Structured data, such as objects of
class
,
struct
，或
union
types, is displayed in the
Locals
and
Expressions
views as part of a tree. To access sub-structures of the objects, expand the tree nodes. The sub-structures are presented in their in-memory order, unless the
Sort Members of Classes and Structs Alphabetically
option from the context menu is selected.
Similarly, pointers are displayed as a tree item with a single child item representing the target of the pointer. In case the context menu item Dereference Pointers Automatically is selected, the pointer and the target are combined into a single entry, showing the name and the type of the pointer and the value of the target.
This standard representation is good enough for the examination of simple structures, but it does usually not give enough insight into more complex structures, such as
QObjects
or associative containers. These items are internally represented by a complex arrangement of pointers, often highly optimized, with part of the data not directly accessible through neither sub-structures nor pointers.
To give the user simple access also to these items, Qt Creator employs Python scripts that are called debugging helpers . Debugging helpers are always automatically used. To force a plain C-like display of structures, select 工具 > Options > Debugger > Locals & Expressions , and then deselect the Use Debugging Helper check box. This will still use the Python scripts, but generate more basic output. To force the plain display for a single object or for all objects of a given type, select the corresponding option from the context menu.
Qt Creator ships with debugging helpers for more than 200 of the most popular Qt classes, standard C++ containers, and smart pointers, covering the usual needs of a C++ application developer out-of-the-box.
Qt Creator uses Python scripts to translate raw memory contents and type information data from native debugger backends (GDB, LLDB, and CDB are currently supported) into the form presented to the user in the Locals and Expressions views.
Unlike GDB's pretty printers and LLDB's data formatters , Qt Creator's debugging helpers are independent of the native debugging backend. That is, the same code can be used with GDB on Linux, LLDB on macOS, and CDB on Windows, or any other platform on which at least one of the three supported backends is available.
To use the default GDB pretty printers installed in your system or linked to the libraries your application uses, select Options > Debugger > GDB > Load system GDB pretty printers 。更多信息，见 Specifying GDB Settings .
You can have commands executed after built-in debugging helpers have been loaded and fully initialized. To load additional debugging helpers or modify existing ones, select 工具 > Options > Debugger > Locals & Expressions , and enter the commands in the Debugging Helper Customization field.
If you receive error messages about receiving signals when using GDB, you can specify
GDB commands
for handling the signals. For example, you can tell GDB to ignore the
SIGSTOP
signal if you receive the following error message:
The inferior stopped because it received a signal from the operating system. Signal name: SIGSTOP
.
To stop GDB from handling the
SIGSTOP
signal, add the following commands to the
Debugging Helper Customization
field:
handle SIGSTOP nopass handle SIGSTOP nostop
To display a message box as soon as your application receives a signal during debugging, select 工具 > Options > Debugger > GDB > Show a message box when receiving a signal .
To add debugging helpers for your own types, no compilation is required, just adding a few lines of Python. The scripts can address multiple versions of Qt, or of your own library, at the same time.
To add debugging helpers for custom types, add debugging helper implementations to the startup file of the native debuggers (for example,
~/.gdbinit
or
~/.lldbinit
) or specify them directly in the
Additional Startup Commands
in
工具
>
Options
>
Debugger
>
GDB
.
To get started with implementing debugging helpers for your own data types, you can put their implementation into the file
share/qtcreator/debugger/personaltypes.py
in your Qt installation or stand-alone Qt Creator installation. On macOS, the file is bundled into the Qt Creator application package, where it is located in the
Contents/resources/debugger
文件夹。
The
personaltypes.py
file contains one example implementation:
# def qdump__MapNode(d, value):
# d.putValue("This is the value column contents")
# d.putExpandable()
# if d.isExpanded():
# with Children(d):
# # Compact simple case.
# d.putSubItem("key", value["key"])
# # Same effect, with more customization possibilities.
# with SubItem(d, "data")
# d.putItem("data", value["data"])
To add debugging helpers:
share/qtcreator/debugger/personaltypes.py
file for editing. For example, if your Qt installation is located in the
Qt5
directory on Windows, look in
C:\Qt5\Tools\QtCreator\share\qtcreator\debugger
. On macOS, look in
Qt5/Qt Creator.app/Contents/resources/debugger
.
personaltypes.py
file. For more information about implementing debugging helpers, see the following sections.
personaltypes.py
from being overwritten when you update your Qt Creator installation (when updating your Qt installation, for example), copy it to a safe location outside the Qt Creator installation in your file system and specify the location in
工具
>
Options
>
Debugger
>
Locals & Expressions
>
Extra Debugging Helpers
.
The custom debugging helpers will be automatically picked up from
personaltypes.py
when you start a debugging session in Qt Creator or select
Reload Debugging Helpers
from the context menu of the
Debugger Log
view.
The implementation of a debugging helper typically consists of a single Python function, which needs to be named
qdump__NS__Foo
, where
NS::Foo
is the class or class template to be examined. Note that the
::
scope resolution operator is replaced by double underscores:
__
. Nested namespaces are possible. Template arguments are not used for the construction of the function name.
范例：
namespace Project { template<typename T> struct Foo {... } }
is
qdump__Project__Foo
.
std::__1::vector<T>::iterator
is
qdump__std____1__vector__iterator
.
Qt Creator's debugger plugin calls this function whenever you want to display an object of this type. The function is passed the following parameters:
d
of type
Dumper
, an object containing the current settings and providing facilities to build up an object representing a part of the
Locals
and
Expressions
views.
value
of type
Value
, wrapping either a
gdb.Value
or an
lldb.SBValue
.
The
qdump__*
function has to feed the Dumper object with certain information that is used to build up the object and its children's display in the
Locals
and
Expressions
views.
范例：
def qdump__QFiniteStack(d, value): alloc = value["_alloc"].integer() size = value["_size"].integer() d.putItemCount(size) if d.isExpanded(): d.putArrayData(value["_array"], size, value.type[0])
注意：
To create dumper functions usable with both LLDB and GDB backends, avoid direct access to the
gdb.*
and
lldb.*
namespaces and use the functions of the
Dumper
class instead.
To get to the base instance of the object in the debugging helper, use the
value.base()
function or the following example code:
def qdump__A(d, value): t = value.members(True)[0].type dptr, base_v = value.split('p{%s}' % t.name) d.putItem(base_v)
Debugging helpers can be set up to be called whenever a type name matches a regular expression. To do so, the debugging helper's function name must begin with
qdump__
(with two underscore characters). In addition, the function needs to have a third parameter called
regex
with a default value that specifies the regular expression that the type name should match.
For example, the Nim 0.12 compiler assigns artificial names, such as
TY1
and
TY2
, to all generic sequences it compiles. To visualize these in Qt Creator, the following debugging helper may be used:
def qdump__NimGenericSequence__(d, value, regex = "^TY.*$"): size = value["Sup"]["len"] base = value["data"].dereference() typeobj = base.dereference().type d.putArrayData(base, size, typeobj)
A debugging helper creates a description of the displayed data item in a format that is similar to GDB/MI and JSON.
For each line in the Locals and Expressions views, a string like the following needs to be created and channeled to the debugger plugin.
{ iname='some internal name', # optional
address='object address in memory', # optional
name='contents of the name column', # optional
value='contents of the value column',
type='contents of the type column',
numchild='number of children', # zero/nonzero is sufficient
children=[ # only needed if item is expanded in view
{iname='internal name of first child',
},
{iname='internal name of second child',
},
]}
The value of the
iname
field is the internal name of the object, which consists of a dot-separated list of identifiers, corresponding to the position of the object's representation in the view. If it is not present, it is generated by concatenating the parent object's
iname
, a dot, and a sequential number.
The value of the
name
field is displayed in the
Name
column of the view. If it is not specified, a simple number in brackets is used instead.
As the format is not guaranteed to be stable, it is strongly recommended not to generate the wire format directly, but to use the abstraction layer provided by the Python Dumper classes, specifically the
Dumper
class itself, and the
Dumper:Value
and
Dumper:Type
abstractions. These provide a complete framework to take care of the
iname
and
addr
fields, to handle children of simple types, references, pointers, enums, and known and unknown structs, as well as some convenience functions to handle common situations.
When using CDB as debugger backend, you can enable the Python dumper by selecting 工具 > Options > Debugger > CDB > Use Python dumper .
The
Dumper
class contains generic bookkeeping, low-level, and convenience functions.
The member functions of the
Dumper
class are the following:
putItem(self, value)
- The
master function
that handles basic types, references, pointers, and enums directly, iterates over base classes and class members of compound types, and calls
qdump__*
functions when appropriate.
putIntItem(self, name, value)
- Equivalent to:
with SubItem(self, name): self . putValue(value) self . putType( "int" )
putBoolItem(self, name, value)
- Equivalent to:
with SubItem(self, name): self . putValue(value) self . putType( "bool" )
putCallItem(self, name, value, func, *args)
- Uses the native debugger backend to place the function call
func
on the value specified by
value
and output the resulting item.
Native calls are extremely powerful and can leverage existing debugging or logging facilities in the debugged process, for example. However, they should only be used in a controlled environment, and only if there is no other way to access the data, for the following reasons:
putArrayData(self, address, itemCount, type)
- Creates the number of children specified by
itemCount
of the type
type
of an array-like object located at
address
.
putSubItem(self, component, value)
- Equivalent to:
with SubItem(self, component): self . putItem(value)
Exceptions raised by nested function calls are caught and all output produced by
putItem
is replaced by the output of:
except RuntimeError:
d.put('value="<invalid>",type="<unknown>",numchild="0",')
put(self, value)
- A low-level function to directly append to the output string. That is also the fastest way to append output.
putField(self, name, value)
- Appends a
name='value'
field.
childRange(self)
- Returns the range of children specified in the current
Children
scope.
putItemCount(self, count)
- Appends the field
value='<%d items>'
to the output.
putName(self, name)
- Appends the
name=''
field.
putType(self, type, priority=0)
- Appends the field
type=''
, unless the
type
coincides with the parent's default child type or
putType
was already called for the current item with a higher value of
priority
.
putBetterType(self, type)
- Overrides the last recorded
type
.
putExpandable(self)
- Announces the existence of child items for the current value. The default are no children.
putNumChild(self, numchild)
- Announces the existence (
numchild
> 0) or non-existence of child items for the current value.
putValue(self, value, encoding = None)
- Appends the file
value=''
, optionally followed by the field
valueencoding=''
。
value
needs to be convertible to a string entirely consisting of alphanumerical values. The
encoding
parameter can be used to specify the encoding in case the real value had to be encoded in some way to meet the alphanumerical-only requirement. The parameter
encoding
is either a string of the form
codec:itemsize:quote
where
codec
is any of
latin1
,
utf8
,
utf16
,
ucs4
,
int
，或
float
.
itemsize
gives the size of the basic component of the object if it is not implied by
codec
and
quote
specifies whether or not the value should be surrounded by quotes in the display.
范例：
# Safe transport of quirky data. Put quotes around the result. d.putValue(d.hexencode("ABC\"DEF"), "utf8:1:1")
putStringValue(self, value)
- Encodes a
QString
and calls
putValue
with the correct
encoding
setting.
putByteArrayValue(self, value)
- Encodes a
QByteArray
and calls
putValue
with the correct
encoding
setting.
isExpanded(self)
- Checks whether the current item is expanded in the view.
createType(self, pattern, size = None)
- Creates a
Dumper.Type
object. The exact operation depends on
pattern
.
pattern
matches the name of a well-known type, a
Dumper.Type
object describing this type is returned.
pattern
is the name of a type known to the native backend, the returned type describes the native type.
pattern
is used to construct a type description by interpreting a sequence of items describing the field of a structure as follows. Field descriptions consist of one or more characters as follows:
q
- Signed 8-byte integral value
Q
- Unsigned 8-byte integral value
i
- Signed 4-byte integral value
I
- Unsigned 4-byte integral value
h
- Signed 2-byte integral value
H
- Unsigned 2-byte integral value
b
- Signed 1-byte integral value
B
- Unsigned 1-byte integral value
d
- 8-byte IEEE 754 floating point value
f
- 4-byte IEEE 754 floating point value
p
- A pointer, that is, an unsigned integral value of suitable size according to the target architecture
@
- Suitable padding. The size is determined by the preceding and following field and the target architecture
<n>s
- A blob of <n> bytes, with implied alignment of 1
<typename>
- A blob of suitable size and suitable alignment determined by a
Dumper.Type
with the name
typename
The
Dumper.Type
class describes the type of a piece of data, typically a C++ class or struct, a pointer to a struct, or a primitive type, such as an integral or floating point type.
Type objects, that is, instances of the
Dumper.Type
class, can be created by native debugger backends, usually by evaluating Debug Information built into or shipped alongside the debugged binary, or created on-the-fly by the debugging helper.
Qt Creator uses the possibility to provide type information on-the-fly for most Qt classes, obliterating the need to use Debug builds of Qt for the purpose of object introspection.
The member functions of the
Dumper.Type
class are the following:
name
- The name of this type as a string, or
None
if the type is anonymous.
size(self)
- Returns the size of an object of this type in bytes.
bitsize(self)
- Returns the size of an object of this type in bits.
alignment(self)
- Returns the required alignment for objects of this type in bytes.
deference(self)
- Returns the dereferences type for pointer type,
None
否则。
pointer(self)
- Returns a pointer type that can be dereferenced to this type.
target(self)
- A convenience function that returns the item type for array types and the dereferenced type for pointers and references.
stripTypedefs(self)
- Returns the underlying type if this type is an alias.
templateArgument(self, position, numeric = False)
- Returns the template parameter located at
position
if this is a templated type. If
numeric
is
True
, returns the parameter as an integral value.
fields(self)
- Returns a list of
Dumper:Fields
describing the base classes and data members of this type.
The
Dumper.Field
class describes a base class or a data member of a type object.
The member function and properties of the
Dumper.Field
class are the following:
isBaseClass
- Distinguishes between base classes and data members.
fieldType(self)
- Returns the type of this base class or data member.
parentType(self)
- Returns the owning type.
bitsize(self)
- Returns the size of this field in bits.
bitpos(self)
- Returns the offset of this field in the owning type in bits.
The
Dumper.Value
class describes a piece of data, such as instances of C++ classes or primitive data types. It can also be used to describe artificial items that have no direct representation in memory, such as file contents, non-contiguous objects, or collections.
A
Dumper.Value
has always an associated
Dumper.Type
. The two main representations of the value's actual data are:
memoryview
，或
bytes
object. The
size()
should match the size of this value's type.
size()
.
Knowledge of the internal representation of a
Dumper.Value
is typically not required when creating a debugger helper for it.
The member function and properties of the
Dumper.Value
class are the following:
integer(self)
- Returns an interpretation of this value as a signed integral value of a suitable size.
pointer(self)
- Returns an interpretation of this value as a pointer in the current address space.
members(self, includeBases)
- Returns a list of
Dumper.Value
objects representing the base objects and data members of this value.
dereference(self)
- For values describing pointers, returns the dereferenced value, and
None
否则。
cast(self, type)
- Returns a value that has the same data as this value, but the type
type
.
address(self)
- Returns the address of this value if it consists of a contiguous region in the current address space, and
None
否则。
data(self)
- Returns the data of this value as a Python
bytes
对象。
split(self, pattern)
- Returns a list of values created according to
pattern
from this value's data. Acceptable patterns are the same as for
Dumper.createType
.
dynamicTypeName(self)
- Tries to retrieve the name of the dynamic type of this value if this is a base class object. Returns
None
if that is not possible.
The attempt to create child items might lead to errors if data is uninitialized or corrupted. To gracefully recover in such situations, use
Children
and
SubItem
Context Managers
to create the nested items.
The
Children
构造函数
__init__(self, dumper, numChild = 1, childType = None, childNumChild = None, maxNumChild = None, addrBase = None, addrStep = None)
uses one mandatory argument and several optional arguments. The mandatory argument refers to the current
Dumper
object. The optional arguments can be used to specify the number
numChild
of children, with type
childType_
and
childNumChild_
grandchildren each. If
maxNumChild
is specified, only that many children are displayed. This should be used when dumping container contents that might take overly long otherwise. The parameters
addrBase
and
addrStep
can be used to reduce the amount of data produced by the child dumpers. Address printing for the
n
th child item will be suppressed if its address equals with
addrBase + n * addrStep
.
范例：
if d.isExpanded(): with Children(d): with SubItem(d): d.putName("key") d.putItem(key) with SubItem(d): d.putName("value") d.putItem(value)
Note that this can be written more conveniently as:
d.putNumChild(2) if d.isExpanded(): with Children(d): d.putSubItem("key", key) d.putSubItem("value", value)