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|
#-----------------------------------------------------------------
# pycparser: cdecl.py
#
# Example of the CDECL tool using pycparser. CDECL "explains" C type
# declarations in plain English.
#
# The AST generated by pycparser from the given declaration is traversed
# recursively to build the explanation. Note that the declaration must be a
# valid external declaration in C. As shown below, typedef can be optionally
# expanded.
#
# For example:
#
# c_decl = 'typedef int Node; const Node* (*ar)[10];'
#
# explain_c_declaration(c_decl)
# => ar is a pointer to array[10] of pointer to const Node
#
# struct and typedef can be optionally expanded:
#
# explain_c_declaration(c_decl, expand_typedef=True)
# => ar is a pointer to array[10] of pointer to const int
#
# c_decl = 'struct P {int x; int y;} p;'
#
# explain_c_declaration(c_decl)
# => p is a struct P
#
# explain_c_declaration(c_decl, expand_struct=True)
# => p is a struct P containing {x is a int, y is a int}
#
# Eli Bendersky [https://eli.thegreenplace.net/]
# License: BSD
#-----------------------------------------------------------------
import copy
import sys
# This is not required if you've installed pycparser into
# your site-packages/ with setup.py
#
sys.path.extend(['.', '..'])
from pycparser import c_parser, c_ast
def explain_c_declaration(c_decl, expand_struct=False, expand_typedef=False):
""" Parses the declaration in c_decl and returns a text
explanation as a string.
The last external node of the string is used, to allow earlier typedefs
for used types.
expand_struct=True will spell out struct definitions recursively.
expand_typedef=True will expand typedef'd types.
"""
parser = c_parser.CParser()
try:
node = parser.parse(c_decl, filename='<stdin>')
except c_parser.ParseError:
e = sys.exc_info()[1]
return "Parse error:" + str(e)
if (not isinstance(node, c_ast.FileAST) or
not isinstance(node.ext[-1], c_ast.Decl)
):
return "Not a valid declaration"
try:
expanded = expand_struct_typedef(node.ext[-1], node,
expand_struct=expand_struct,
expand_typedef=expand_typedef)
except Exception as e:
return "Not a valid declaration: " + str(e)
return _explain_decl_node(expanded)
def _explain_decl_node(decl_node):
""" Receives a c_ast.Decl note and returns its explanation in
English.
"""
storage = ' '.join(decl_node.storage) + ' ' if decl_node.storage else ''
return (decl_node.name +
" is a " +
storage +
_explain_type(decl_node.type))
def _explain_type(decl):
""" Recursively explains a type decl node
"""
typ = type(decl)
if typ == c_ast.TypeDecl:
quals = ' '.join(decl.quals) + ' ' if decl.quals else ''
return quals + _explain_type(decl.type)
elif typ == c_ast.Typename or typ == c_ast.Decl:
return _explain_type(decl.type)
elif typ == c_ast.IdentifierType:
return ' '.join(decl.names)
elif typ == c_ast.PtrDecl:
quals = ' '.join(decl.quals) + ' ' if decl.quals else ''
return quals + 'pointer to ' + _explain_type(decl.type)
elif typ == c_ast.ArrayDecl:
arr = 'array'
if decl.dim: arr += '[%s]' % decl.dim.value
return arr + " of " + _explain_type(decl.type)
elif typ == c_ast.FuncDecl:
if decl.args:
params = [_explain_type(param) for param in decl.args.params]
args = ', '.join(params)
else:
args = ''
return ('function(%s) returning ' % (args) +
_explain_type(decl.type))
elif typ == c_ast.Struct:
decls = [_explain_decl_node(mem_decl) for mem_decl in decl.decls]
members = ', '.join(decls)
return ('struct%s ' % (' ' + decl.name if decl.name else '') +
('containing {%s}' % members if members else ''))
def expand_struct_typedef(cdecl, file_ast,
expand_struct=False,
expand_typedef=False):
"""Expand struct & typedef and return a new expanded node."""
decl_copy = copy.deepcopy(cdecl)
_expand_in_place(decl_copy, file_ast, expand_struct, expand_typedef)
return decl_copy
def _expand_in_place(decl, file_ast, expand_struct=False, expand_typedef=False):
"""Recursively expand struct & typedef in place, throw RuntimeError if
undeclared struct or typedef are used
"""
typ = type(decl)
if typ in (c_ast.Decl, c_ast.TypeDecl, c_ast.PtrDecl, c_ast.ArrayDecl):
decl.type = _expand_in_place(decl.type, file_ast, expand_struct,
expand_typedef)
elif typ == c_ast.Struct:
if not decl.decls:
struct = _find_struct(decl.name, file_ast)
if not struct:
raise RuntimeError('using undeclared struct %s' % decl.name)
decl.decls = struct.decls
for i, mem_decl in enumerate(decl.decls):
decl.decls[i] = _expand_in_place(mem_decl, file_ast, expand_struct,
expand_typedef)
if not expand_struct:
decl.decls = []
elif (typ == c_ast.IdentifierType and
decl.names[0] not in ('int', 'char')):
typedef = _find_typedef(decl.names[0], file_ast)
if not typedef:
raise RuntimeError('using undeclared type %s' % decl.names[0])
if expand_typedef:
return typedef.type
return decl
def _find_struct(name, file_ast):
"""Receives a struct name and return declared struct object in file_ast
"""
for node in file_ast.ext:
if (type(node) == c_ast.Decl and
type(node.type) == c_ast.Struct and
node.type.name == name):
return node.type
def _find_typedef(name, file_ast):
"""Receives a type name and return typedef object in file_ast
"""
for node in file_ast.ext:
if type(node) == c_ast.Typedef and node.name == name:
return node
if __name__ == "__main__":
if len(sys.argv) > 1:
c_decl = sys.argv[1]
else:
c_decl = "char *(*(**foo[][8])())[];"
print("Explaining the declaration: " + c_decl + "\n")
print(explain_c_declaration(c_decl) + "\n")
|
