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gdb represents types from the inferior using the class
gdb.Type
.
The following type-related functions are available in the gdb
module:
This function looks up a type by its name, which must be a string.
If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Ordinarily, this function will return an instance of
gdb.Type
. If the named type cannot be found, it will throw an exception.
Integer types can be found without looking them up by name.
See Architectures In Python, for the integer_type
method.
If the type is a structure or class type, or an enum type, the fields
of that type can be accessed using the Python dictionary syntax.
For example, if some_type
is a gdb.Type
instance holding
a structure type, you can access its foo
field with:
bar = some_type['foo']
bar
will be a gdb.Field
object; see below under the
description of the Type.fields
method for a description of the
gdb.Field
class.
An instance of Type
has the following attributes:
The alignment of this type, in bytes. Type alignment comes from the debugging information; if it was not specified, then gdb will use the relevant ABI to try to determine the alignment. In some cases, even this is not possible, and zero will be returned.
The type code for this type. The type code will be one of the
TYPE_CODE_
constants defined below.
A boolean indicating whether this type is dynamic. In some situations, such as Rust
enum
types or Ada variant records, the concrete type of a value may vary depending on its contents. That is, the declared type of a variable, or the type returned bygdb.lookup_type
may be dynamic; while the type of the variable's value will be a concrete instance of that dynamic type.For example, consider this code:
int n; int array[n];Here, at least conceptually (whether your compiler actually does this is a separate issue), examining
gdb.lookup_symbol("array", ...).type
could yield agdb.Type
which reports a size ofNone
. This is the dynamic type.However, examining
gdb.parse_and_eval("array").type
would yield a concrete type, whose length would be known.
The size of this type, in target
char
units. Usually, a target'schar
type will be an 8-bit byte. However, on some unusual platforms, this type may have a different size. A dynamic type may not have a fixed size; in this case, this attribute's value will beNone
.
The tag name for this type. The tag name is the name after
struct
,union
, orenum
in C and C++; not all languages have this concept. If this type has no tag name, thenNone
is returned.
The
gdb.Objfile
that this type was defined in, orNone
if there is no associated objfile.
This property is
True
if the type is a scalar type, otherwise, this property isFalse
. Examples of non-scalar types include structures, unions, and classes.
For scalar types (those for which
Type.is_scalar
isTrue
), this property isTrue
if the type is signed, otherwise this property isFalse
.Attempting to read this property for a non-scalar type (a type for which
Type.is_scalar
isFalse
), will raise aValueError
.
The following methods are provided:
Return the fields of this type. The behavior depends on the type code:
- For structure and union types, this method returns the fields.
- Range types have two fields, the minimum and maximum values.
- Enum types have one field per enum constant.
- Function and method types have one field per parameter. The base types of C++ classes are also represented as fields.
- Array types have one field representing the array's range.
- If the type does not fit into one of these categories, a
TypeError
is raised.Each field is a
gdb.Field
object, with some pre-defined attributes:
bitpos
- This attribute is not available for
enum
orstatic
(as in C++) fields. The value is the position, counting in bits, from the start of the containing type. Note that, in a dynamic type, the position of a field may not be constant. In this case, the value will beNone
. Also, a dynamic type may have fields that do not appear in a corresponding concrete type.enumval
- This attribute is only available for
enum
fields, and its value is the enumeration member's integer representation.name
- The name of the field, or
None
for anonymous fields.artificial
- This is
True
if the field is artificial, usually meaning that it was provided by the compiler and not the user. This attribute is always provided, and isFalse
if the field is not artificial.is_base_class
- This is
True
if the field represents a base class of a C++ structure. This attribute is always provided, and isFalse
if the field is not a base class of the type that is the argument offields
, or if that type was not a C++ class.bitsize
- If the field is packed, or is a bitfield, then this will have a non-zero value, which is the size of the field in bits. Otherwise, this will be zero; in this case the field's size is given by its type.
type
- The type of the field. This is usually an instance of
Type
, but it can beNone
in some situations.parent_type
- The type which contains this field. This is an instance of
gdb.Type
.
Return a new
gdb.Type
object which represents an array of this type. If one argument is given, it is the inclusive upper bound of the array; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the array, and the second argument is the upper bound of the array. An array's length must not be negative, but the bounds can be.
Return a new
gdb.Type
object which represents a vector of this type. If one argument is given, it is the inclusive upper bound of the vector; in this case the lower bound is zero. If two arguments are given, the first argument is the lower bound of the vector, and the second argument is the upper bound of the vector. A vector's length must not be negative, but the bounds can be.The difference between an
array
and avector
is that arrays behave like in C: when used in expressions they decay to a pointer to the first element whereas vectors are treated as first class values.
Return a new
gdb.Type
object which represents aconst
-qualified variant of this type.
Return a new
gdb.Type
object which represents avolatile
-qualified variant of this type.
Return a new
gdb.Type
object which represents an unqualified variant of this type. That is, the result is neitherconst
norvolatile
.
Return a Python
Tuple
object that contains two elements: the low bound of the argument type and the high bound of that type. If the type does not have a range, gdb will raise agdb.error
exception (see Exception Handling).
Return a new
gdb.Type
object which represents a reference to this type.
Return a new
gdb.Type
that represents the real type, after removing all layers of typedefs.
Return a new
gdb.Type
object which represents the target type of this type.For a pointer type, the target type is the type of the pointed-to object. For an array type (meaning C-like arrays), the target type is the type of the elements of the array. For a function or method type, the target type is the type of the return value. For a complex type, the target type is the type of the elements. For a typedef, the target type is the aliased type.
If the type does not have a target, this method will throw an exception.
If this
gdb.Type
is an instantiation of a template, this will return a newgdb.Value
orgdb.Type
which represents the value of the nth template argument (indexed starting at 0).If this
gdb.Type
is not a template type, or if the type has fewer than n template arguments, this will throw an exception. Ordinarily, only C++ code will have template types.If block is given, then name is looked up in that scope. Otherwise, it is searched for globally.
Return
gdb.Value
instance of this type whose value is optimized out. This allows a frame decorator to indicate that the value of an argument or a local variable is not known.
Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the gdb
module:
gdb.TYPE_CODE_PTR
gdb.TYPE_CODE_ARRAY
gdb.TYPE_CODE_STRUCT
gdb.TYPE_CODE_UNION
gdb.TYPE_CODE_ENUM
gdb.TYPE_CODE_FLAGS
gdb.TYPE_CODE_FUNC
gdb.TYPE_CODE_INT
gdb.TYPE_CODE_FLT
gdb.TYPE_CODE_VOID
void
.
gdb.TYPE_CODE_SET
gdb.TYPE_CODE_RANGE
gdb.TYPE_CODE_STRING
gdb.TYPE_CODE_BITSTRING
gdb.TYPE_CODE_ERROR
gdb.TYPE_CODE_METHOD
gdb.TYPE_CODE_METHODPTR
gdb.TYPE_CODE_MEMBERPTR
gdb.TYPE_CODE_REF
gdb.TYPE_CODE_RVALUE_REF
gdb.TYPE_CODE_CHAR
gdb.TYPE_CODE_BOOL
gdb.TYPE_CODE_COMPLEX
gdb.TYPE_CODE_TYPEDEF
gdb.TYPE_CODE_NAMESPACE
gdb.TYPE_CODE_DECFLOAT
gdb.TYPE_CODE_INTERNAL_FUNCTION
gdb.TYPE_CODE_XMETHOD
gdb.TYPE_CODE_FIXED_POINT
gdb.TYPE_CODE_NAMESPACE
Further support for types is provided in the gdb.types
Python module (see gdb.types).