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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. All the types used in it must be defined with
# typedef, or parsing will fail. The definition can be arbitrary - pycparser
# doesn't really care what the type is defined to be, only that it's a type.
#
# For example:
#
# 'typedef int Node; const Node* (*ar)[10];'
# =>
# ar is a pointer to array[10] of pointer to const Node
#
# Copyright (C) 2008-2015, Eli Bendersky
# License: BSD
#-----------------------------------------------------------------
import sys
from pycparser import c_parser, c_ast
def explain_c_declaration(c_decl):
""" 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.
"""
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"
return _explain_decl_node(node.ext[-1])
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))
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")
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