cef/tools/make_ctocpp_impl.py

# Copyright (c) 2011 The Chromium Embedded Framework Authors. All rights
# reserved. Use of this source code is governed by a BSD-style license that
# can be found in the LICENSE file.

from cef_parser import *

def make_ctocpp_impl_proto(clsname, name, func, parts):
    const = ''

    if clsname is None:
        proto = 'CEF_GLOBAL '+parts['retval']+' '
    else:
        proto = parts['retval']+' '+clsname
        if isinstance(func, obj_function_virtual):
            proto += 'CToCpp'
            if func.is_const():
                const = ' const'

        proto += '::'

    proto += name+'('+string.join(parts['args'], ', ')+')'+const
    return proto

def make_ctocpp_function_impl_existing(clsname, name, func, impl):
    notify(name+' has manual edits')

    # retrieve the C++ prototype parts
    parts = func.get_cpp_parts(True)

    changes = format_translation_changes(impl, parts)
    if len(changes) > 0:
        notify(name+' prototype changed')

    return wrap_code(make_ctocpp_impl_proto(clsname, name, func, parts))+'{'+ \
           changes+impl['body']+'\n}\n'

def make_ctocpp_function_impl_new(clsname, name, func):
    # build the C++ prototype
    parts = func.get_cpp_parts(True)
    result = make_ctocpp_impl_proto(clsname, name, func, parts)+' {'

    if isinstance(func, obj_function_virtual):
        # determine how the struct should be referenced
        if clsname == func.parent.get_name():
            result += '\n  '+get_capi_name(clsname, True)+'* _struct = GetStruct();'
        else:
            result += '\n  '+func.parent.get_capi_name()+'* _struct = reinterpret_cast<'+\
                      func.parent.get_capi_name()+'*>(GetStruct());'

    invalid = []

    # retrieve the function arguments
    args = func.get_arguments()

    # determine the argument types
    for arg in args:
        if arg.get_arg_type() == 'invalid':
            invalid.append(arg.get_name())

    # retrieve the function return value
    retval = func.get_retval()
    retval_type = retval.get_retval_type()
    if retval_type == 'invalid':
        invalid.append('(return value)')
        retval_default = ''
    else:
        retval_default = retval.get_retval_default(False)
        if len(retval_default) > 0:
            retval_default = ' '+retval_default;

    # add API hash check
    if func.has_attrib('api_hash_check'):
        result += '\n  const char* api_hash = cef_api_hash(0);'\
                  '\n  if (strcmp(api_hash, CEF_API_HASH_PLATFORM)) {'\
                  '\n    // The libcef API hash does not match the current header API hash.'\
                  '\n    NOTREACHED();'\
                  '\n    return'+retval_default+';'\
                  '\n  }\n'

    if isinstance(func, obj_function_virtual):
        # add the structure size check
        result += '\n  if (CEF_MEMBER_MISSING(_struct, '+func.get_capi_name()+'))'
        result += '\n    return'+retval_default+';\n'

    if len(invalid) > 0:
        notify(name+' could not be autogenerated')
        # code could not be auto-generated
        result += '\n  // BEGIN DELETE BEFORE MODIFYING'
        result += '\n  // AUTO-GENERATED CONTENT'
        result += '\n  // COULD NOT IMPLEMENT DUE TO: '+string.join(invalid, ', ')
        result += '\n  #pragma message("Warning: "__FILE__": '+name+' is not implemented")'
        result += '\n  // END DELETE BEFORE MODIFYING'
        result += '\n}\n\n'
        return wrap_code(result)

    result += '\n  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING\n'

    result_len = len(result)

    optional = []

    # parameter verification
    for arg in args:
        arg_type = arg.get_arg_type()
        arg_name = arg.get_type().get_name()

        # skip optional params
        optional_params = arg.parent.get_attrib_list('optional_param')
        if not optional_params is None and arg_name in optional_params:
            optional.append(arg_name)
            continue

        comment = '\n  // Verify param: '+arg_name+'; type: '+arg_type

        if arg_type == 'simple_byaddr' or arg_type == 'bool_byaddr':
            result += comment+\
                      '\n  DCHECK('+arg_name+');'\
                      '\n  if (!'+arg_name+')'\
                      '\n    return'+retval_default+';'
        elif arg_type == 'refptr_same' or arg_type == 'refptr_diff':
            result += comment+\
                      '\n  DCHECK('+arg_name+'.get());'\
                      '\n  if (!'+arg_name+'.get())'\
                      '\n    return'+retval_default+';'
        elif arg_type == 'string_byref_const':
            result += comment+\
                      '\n  DCHECK(!'+arg_name+'.empty());'\
                      '\n  if ('+arg_name+'.empty())'\
                      '\n    return'+retval_default+';'

        # check index params
        index_params = arg.parent.get_attrib_list('index_param')
        if not index_params is None and arg_name in index_params:
            result += comment+\
                      '\n  DCHECK_GE('+arg_name+', 0);'\
                      '\n  if ('+arg_name+' < 0)'\
                      '\n    return'+retval_default+';'

    if len(optional) > 0:
        # Wrap the comment at 80 characters.
        str = '\n  // Unverified params: ' + optional[0]
        for name in optional[1:]:
            str += ','
            if len(str) + len(name) + 1 > 80:
                result += str
                str = '\n  //'
            str += ' ' + name
        result += str

    if len(result) != result_len:
        result += '\n'
    result_len = len(result)

    # parameter translation
    params = []
    if isinstance(func, obj_function_virtual):
        params.append('_struct')

    for arg in args:
        arg_type = arg.get_arg_type()
        arg_name = arg.get_type().get_name()

        comment = '\n  // Translate param: '+arg_name+'; type: '+arg_type

        if arg_type == 'simple_byval' or arg_type == 'simple_byaddr' or \
           arg_type == 'bool_byval':
            params.append(arg_name)
        elif arg_type == 'simple_byref' or arg_type == 'simple_byref_const' or \
            arg_type == 'struct_byref_const' or arg_type == 'struct_byref':
            params.append('&'+arg_name)
        elif arg_type == 'bool_byref':
            result += comment+\
                      '\n  int '+arg_name+'Int = '+arg_name+';'
            params.append('&'+arg_name+'Int')
        elif arg_type == 'bool_byaddr':
            result += comment+\
                      '\n  int '+arg_name+'Int = '+arg_name+'?*'+arg_name+':0;'
            params.append('&'+arg_name+'Int')
        elif arg_type == 'string_byref_const':
            params.append(arg_name+'.GetStruct()')
        elif arg_type == 'string_byref':
            params.append(arg_name+'.GetWritableStruct()')
        elif arg_type == 'refptr_same':
            refptr_class = arg.get_type().get_refptr_type()
            params.append(refptr_class+'CToCpp::Unwrap('+arg_name+')')
        elif arg_type == 'refptr_diff':
            refptr_class = arg.get_type().get_refptr_type()
            params.append(refptr_class+'CppToC::Wrap('+arg_name+')')
        elif arg_type == 'refptr_same_byref' or arg_type == 'refptr_diff_byref':
            refptr_class = arg.get_type().get_refptr_type()
            refptr_struct = arg.get_type().get_result_refptr_type_root()
            if arg_type == 'refptr_same_byref':
                assign = refptr_class+'CToCpp::Unwrap('+arg_name+')'
            else:
                assign = refptr_class+'CppToC::Wrap('+arg_name+')'
            result += comment+\
                      '\n  '+refptr_struct+'* '+arg_name+'Struct = NULL;'\
                      '\n  if ('+arg_name+'.get())'\
                      '\n    '+arg_name+'Struct = '+assign+';'\
                      '\n  '+refptr_struct+'* '+arg_name+'Orig = '+arg_name+'Struct;'
            params.append('&'+arg_name+'Struct')
        elif arg_type == 'string_vec_byref' or arg_type == 'string_vec_byref_const':
            result += comment+\
                      '\n  cef_string_list_t '+arg_name+'List = cef_string_list_alloc();'\
                      '\n  DCHECK('+arg_name+'List);'\
                      '\n  if ('+arg_name+'List)'\
                      '\n    transfer_string_list_contents('+arg_name+', '+arg_name+'List);'
            params.append(arg_name+'List')
        elif arg_type == 'string_map_single_byref' or arg_type == 'string_map_single_byref_const':
            result += comment+\
                      '\n  cef_string_map_t '+arg_name+'Map = cef_string_map_alloc();'\
                      '\n  DCHECK('+arg_name+'Map);'\
                      '\n  if ('+arg_name+'Map)'\
                      '\n    transfer_string_map_contents('+arg_name+', '+arg_name+'Map);'
            params.append(arg_name+'Map')
        elif arg_type == 'string_map_multi_byref' or arg_type == 'string_map_multi_byref_const':
            result += comment+\
                      '\n  cef_string_multimap_t '+arg_name+'Multimap = cef_string_multimap_alloc();'\
                      '\n  DCHECK('+arg_name+'Multimap);'\
                      '\n  if ('+arg_name+'Multimap)'\
                      '\n    transfer_string_multimap_contents('+arg_name+', '+arg_name+'Multimap);'
            params.append(arg_name+'Multimap')
        elif arg_type == 'simple_vec_byref' or arg_type == 'bool_vec_byref' or \
             arg_type == 'refptr_vec_same_byref' or arg_type == 'refptr_vec_diff_byref':
            count_func = arg.get_attrib_count_func()
            vec_type = arg.get_type().get_result_vector_type_root()
            if arg_type == 'refptr_vec_same_byref':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CToCpp::Unwrap('+arg_name+'[i])'
            elif arg_type == 'refptr_vec_diff_byref':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CppToC::Wrap('+arg_name+'[i])'
            else:
                assign = arg_name+'[i]'
            result += comment+\
                      '\n  size_t '+arg_name+'Size = '+arg_name+'.size();'\
                      '\n  size_t '+arg_name+'Count = std::max('+count_func+'(), '+arg_name+'Size);'\
                      '\n  '+vec_type+'* '+arg_name+'List = NULL;'\
                      '\n  if ('+arg_name+'Count > 0) {'\
                      '\n    '+arg_name+'List = new '+vec_type+'['+arg_name+'Count];'\
                      '\n    DCHECK('+arg_name+'List);'\
                      '\n    if ('+arg_name+'List) {'\
                      '\n       memset('+arg_name+'List, 0, sizeof('+vec_type+')*'+arg_name+'Count);'\
                      '\n    }'\
                      '\n    if ('+arg_name+'List && '+arg_name+'Size > 0) {'\
                      '\n      for (size_t i = 0; i < '+arg_name+'Size; ++i) {'\
                      '\n        '+arg_name+'List[i] = '+assign+';'\
                      '\n      }'\
                      '\n    }'\
                      '\n  }'
            params.append('&'+arg_name+'Count')
            params.append(arg_name+'List')
        elif arg_type == 'simple_vec_byref_const' or arg_type == 'bool_vec_byref_const' or \
             arg_type == 'refptr_vec_same_byref_const' or arg_type == 'refptr_vec_diff_byref_const':
            count_func = arg.get_attrib_count_func()
            vec_type = arg.get_type().get_result_vector_type_root()
            if arg_type == 'refptr_vec_same_byref_const':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CToCpp::Unwrap('+arg_name+'[i])'
            elif arg_type == 'refptr_vec_diff_byref_const':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CppToC::Wrap('+arg_name+'[i])'
            else:
                assign = arg_name+'[i]'
            result += comment+\
                      '\n  const size_t '+arg_name+'Count = '+arg_name+'.size();'\
                      '\n  '+vec_type+'* '+arg_name+'List = NULL;'\
                      '\n  if ('+arg_name+'Count > 0) {'\
                      '\n    '+arg_name+'List = new '+vec_type+'['+arg_name+'Count];'\
                      '\n    DCHECK('+arg_name+'List);'\
                      '\n    if ('+arg_name+'List) {'\
                      '\n      for (size_t i = 0; i < '+arg_name+'Count; ++i) {'\
                      '\n        '+arg_name+'List[i] = '+assign+';'\
                      '\n      }'\
                      '\n    }'\
                      '\n  }'
            params.append(arg_name+'Count')
            params.append(arg_name+'List')

    if len(result) != result_len:
        result += '\n'
    result_len = len(result)

    # execution
    result += '\n  // Execute\n  '

    if retval_type != 'none':
        # has a return value
        if retval_type == 'simple' or retval_type == 'bool':
            result += retval.get_type().get_result_simple_type_root()
        elif retval_type == 'string':
            result += 'cef_string_userfree_t'
        elif retval_type == 'refptr_same' or retval_type == 'refptr_diff':
            refptr_struct = retval.get_type().get_result_refptr_type_root()
            result += refptr_struct+'*'

        result += ' _retval = '

    if isinstance(func, obj_function_virtual):
        result += '_struct->'
    result += func.get_capi_name()+'('

    if len(params) > 0:
        if not isinstance(func, obj_function_virtual):
            result += '\n      '
        result += string.join(params,',\n      ')

    result += ');\n'

    result_len = len(result)

    # parameter restoration
    for arg in args:
        arg_type = arg.get_arg_type()
        arg_name = arg.get_type().get_name()

        comment = '\n  // Restore param:'+arg_name+'; type: '+arg_type

        if arg_type == 'bool_byref':
            result += comment+\
                      '\n  '+arg_name+' = '+arg_name+'Int?true:false;'
        elif arg_type == 'bool_byaddr':
            result += comment+\
                      '\n  if ('+arg_name+')'\
                      '\n    *'+arg_name+' = '+arg_name+'Int?true:false;'
        elif arg_type == 'refptr_same_byref' or arg_type == 'refptr_diff_byref':
            refptr_class = arg.get_type().get_refptr_type()
            refptr_struct = arg.get_type().get_result_refptr_type_root()
            if arg_type == 'refptr_same_byref':
                assign = refptr_class+'CToCpp::Wrap('+arg_name+'Struct)'
            else:
                assign = refptr_class+'CppToC::Unwrap('+arg_name+'Struct)'
            result += comment+\
                      '\n  if ('+arg_name+'Struct) {'\
                      '\n    if ('+arg_name+'Struct != '+arg_name+'Orig) {'\
                      '\n      '+arg_name+' = '+assign+';'\
                      '\n    }'\
                      '\n  } else {'\
                      '\n    '+arg_name+' = NULL;'\
                      '\n  }'
        elif arg_type == 'string_vec_byref':
            result += comment+\
                      '\n  if ('+arg_name+'List) {'\
                      '\n    '+arg_name+'.clear();'\
                      '\n    transfer_string_list_contents('+arg_name+'List, '+arg_name+');'\
                      '\n    cef_string_list_free('+arg_name+'List);'\
                      '\n  }'
        elif arg_type == 'string_vec_byref_const':
            result += comment+\
                      '\n  if ('+arg_name+'List)'\
                      '\n    cef_string_list_free('+arg_name+'List);'
        elif arg_type == 'string_map_single_byref':
            result += comment+\
                      '\n  if ('+arg_name+'Map) {'\
                      '\n    '+arg_name+'.clear();'\
                      '\n    transfer_string_map_contents('+arg_name+'Map, '+arg_name+');'\
                      '\n    cef_string_map_free('+arg_name+'Map);'\
                      '\n  }'
        elif arg_type == 'string_map_single_byref_const':
            result += comment+\
                      '\n  if ('+arg_name+'Map)'\
                      '\n    cef_string_map_free('+arg_name+'Map);'
        elif arg_type == 'string_map_multi_byref':
            result += comment+\
                      '\n  if ('+arg_name+'Multimap) {'\
                      '\n    '+arg_name+'.clear();'\
                      '\n    transfer_string_multimap_contents('+arg_name+'Multimap, '+arg_name+');'\
                      '\n    cef_string_multimap_free('+arg_name+'Multimap);'\
                      '\n  }'
        elif arg_type == 'string_map_multi_byref_const':
            result += comment+\
                      '\n  if ('+arg_name+'Multimap)'\
                      '\n    cef_string_multimap_free('+arg_name+'Multimap);'
        elif arg_type == 'simple_vec_byref' or arg_type == 'bool_vec_byref' or \
             arg_type == 'refptr_vec_same_byref' or arg_type == 'refptr_vec_diff_byref':
            count_func = arg.get_attrib_count_func()
            vec_type = arg.get_type().get_result_vector_type_root()
            if arg_type == 'refptr_vec_same_byref':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CToCpp::Wrap('+arg_name+'List[i])'
            elif arg_type == 'refptr_vec_diff_byref':
                refptr_class = arg.get_type().get_refptr_type()
                assign = refptr_class+'CppToC::Unwrap('+arg_name+'List[i])'
            elif arg_type == 'bool_vec_byref':
                assign = arg_name+'List[i]?true:false'
            else:
                assign = arg_name+'List[i]'
            result += comment+\
                      '\n  '+arg_name+'.clear();'\
                      '\n  if ('+arg_name+'Count > 0 && '+arg_name+'List) {'\
                      '\n    for (size_t i = 0; i < '+arg_name+'Count; ++i) {'\
                      '\n      '+arg_name+'.push_back('+assign+');'\
                      '\n    }'\
                      '\n    delete [] '+arg_name+'List;'\
                      '\n  }'
        elif arg_type == 'simple_vec_byref_const' or arg_type == 'bool_vec_byref_const' or \
             arg_type == 'refptr_vec_same_byref_const' or arg_type == 'refptr_vec_diff_byref_const':
            result += comment+\
                      '\n  if ('+arg_name+'List)'\
                      '\n    delete [] '+arg_name+'List;'

    if len(result) != result_len:
        result += '\n'
    result_len = len(result)

    # special handling for the global CefShutdown function
    if name == 'CefShutdown' and isinstance(func.parent, obj_header):
        classes = func.parent.get_classes()

        names = []
        for cls in classes:
            if cls.has_attrib('no_debugct_check'):
                continue;

            if cls.is_library_side():
                names.append(cls.get_name()+'CToCpp')
            else:
                names.append(cls.get_name()+'CppToC')

        if len(names) > 0:
            names = sorted(names)
            result += '\n#ifndef NDEBUG'\
                      '\n  // Check that all wrapper objects have been destroyed'
            for name in names:
                result += '\n  DCHECK(base::AtomicRefCountIsZero(&'+name+'::DebugObjCt));';
            result += '\n#endif  // !NDEBUG'

    if len(result) != result_len:
        result += '\n'
    result_len = len(result)

    # return translation
    if retval_type != 'none':
        # has a return value
        result += '\n  // Return type: '+retval_type
        if retval_type == 'simple':
            result += '\n  return _retval;'
        elif retval_type == 'bool':
            result += '\n  return _retval?true:false;'
        elif retval_type == 'string':
            result += '\n  CefString _retvalStr;'\
                      '\n  _retvalStr.AttachToUserFree(_retval);'\
                      '\n  return _retvalStr;'
        elif retval_type == 'refptr_same':
            refptr_class = retval.get_type().get_refptr_type()
            result += '\n  return '+refptr_class+'CToCpp::Wrap(_retval);'
        elif retval_type == 'refptr_diff':
            refptr_class = retval.get_type().get_refptr_type()
            result += '\n  return '+refptr_class+'CppToC::Unwrap(_retval);'

    if len(result) != result_len:
        result += '\n'

    result += '}\n'
    return wrap_code(result)

def make_ctocpp_function_impl(clsname, funcs, existing):
    impl = ''

    for func in funcs:
        name = func.get_name()
        value = get_next_function_impl(existing, name)
        if not value is None \
            and value['body'].find('// AUTO-GENERATED CONTENT') < 0:
            # an implementation exists that was not auto-generated
            impl += make_ctocpp_function_impl_existing(clsname, name, func, value)
        else:
            impl += make_ctocpp_function_impl_new(clsname, name, func)

    return impl

def make_ctocpp_virtual_function_impl(header, cls, existing):
    impl = make_ctocpp_function_impl(cls.get_name(), cls.get_virtual_funcs(), existing)

    cur_cls = cls
    while True:
        parent_name = cur_cls.get_parent_name()
        if parent_name == 'CefBase':
            break
        else:
            parent_cls = header.get_class(parent_name)
            if parent_cls is None:
                raise Exception('Class does not exist: '+parent_name)
            impl += make_ctocpp_function_impl(cls.get_name(), parent_cls.get_virtual_funcs(), existing)
        cur_cls = header.get_class(parent_name)
    
    return impl

def make_ctocpp_unwrap_derived(header, cls):
    # identify all classes that derive from cls
    derived_classes = []
    clsname = cls.get_name()
    allclasses = header.get_classes()
    for cur_cls in allclasses:
        if cur_cls.get_name() == clsname:
            continue
        if cur_cls.has_parent(clsname):
            derived_classes.append(cur_cls.get_name())

    derived_classes = sorted(derived_classes)
    
    impl = ''
    for clsname in derived_classes:
      impl += '  if (type == '+get_wrapper_type_enum(clsname)+') {\n'+\
              '    return reinterpret_cast<'+get_capi_name(cls.get_name(), True)+'*>('+\
              clsname+'CToCpp::Unwrap(reinterpret_cast<'+clsname+'*>(c)));\n'+\
              '  }\n'
    return impl

def make_ctocpp_class_impl(header, clsname, impl):
    cls = header.get_class(clsname)
    if cls is None:
        raise Exception('Class does not exist: '+clsname)

    capiname = cls.get_capi_name()

    # retrieve the existing virtual function implementations
    existing = get_function_impls(impl, clsname+'CToCpp::')

    # generate virtual functions
    virtualimpl = make_ctocpp_virtual_function_impl(header, cls, existing)
    if len(virtualimpl) > 0:
        virtualimpl = '\n// VIRTUAL METHODS - Body may be edited by hand.\n\n'+virtualimpl

    # retrieve the existing static function implementations
    existing = get_function_impls(impl, clsname+'::')

    # generate static functions
    staticimpl = make_ctocpp_function_impl(clsname, cls.get_static_funcs(), existing)
    if len(staticimpl) > 0:
        staticimpl = '\n// STATIC METHODS - Body may be edited by hand.\n\n'+staticimpl

    resultingimpl = staticimpl + virtualimpl
    
    # any derived classes can be unwrapped
    unwrapderived = make_ctocpp_unwrap_derived(header, cls)

    # determine what includes are required by identifying what translation
    # classes are being used
    includes = format_translation_includes(header, resultingimpl + unwrapderived)

    # build the final output
    result = get_copyright()

    result += includes+'\n'+resultingimpl+'\n'

    parent_sig = 'CefCToCpp<'+clsname+'CToCpp, '+clsname+', '+capiname+'>'

    const =  '// CONSTRUCTOR - Do not edit by hand.\n\n'+ \
             clsname+'CToCpp::'+clsname+'CToCpp() {\n'+ \
             '}\n\n'+ \
             'template<> '+capiname+'* '+parent_sig+'::UnwrapDerived(CefWrapperType type, '+clsname+'* c) {\n'+ \
             unwrapderived + \
             '  NOTREACHED() << "Unexpected class type: " << type;\n'+ \
             '  return NULL;\n'+ \
             '}\n\n'+ \
             '#ifndef NDEBUG\n'+ \
             'template<> base::AtomicRefCount '+parent_sig+'::DebugObjCt = 0;\n'+ \
             '#endif\n\n'+ \
             'template<> CefWrapperType '+parent_sig+'::kWrapperType = '+get_wrapper_type_enum(clsname)+';'

    result += wrap_code(const)

    return result

def make_ctocpp_global_impl(header, impl):
    # retrieve the existing global function implementations
    existing = get_function_impls(impl, 'CEF_GLOBAL')

    # generate static functions
    impl = make_ctocpp_function_impl(None, header.get_funcs(), existing)
    if len(impl) > 0:
        impl = '\n// GLOBAL METHODS - Body may be edited by hand.\n\n'+impl

    includes = ''

    # include required headers for global functions
    filenames = []
    for func in header.get_funcs():
        filename = func.get_file_name()
        if not filename in filenames:
            includes += '#include "include/'+func.get_file_name()+'"\n' \
                        '#include "include/capi/'+func.get_capi_file_name()+'"\n'
            filenames.append(filename)

    # determine what includes are required by identifying what translation
    # classes are being used
    includes += format_translation_includes(header, impl)

    # build the final output
    result = get_copyright()

    result += includes+'\n// Define used to facilitate parsing.\n#define CEF_GLOBAL\n\n'+impl

    return result

def write_ctocpp_impl(header, clsname, dir, backup):
    if clsname is None:
        # global file
        file = dir
    else:
        # class file
        # give the output file the same directory offset as the input file
        cls = header.get_class(clsname)
        dir = os.path.dirname(os.path.join(dir, cls.get_file_name()))
        file = os.path.join(dir, get_capi_name(clsname[3:], False)+'_ctocpp.cc')

    if path_exists(file):
        oldcontents = read_file(file)
    else:
        oldcontents = ''

    if clsname is None:
        newcontents = make_ctocpp_global_impl(header, oldcontents)
    else:
        newcontents = make_ctocpp_class_impl(header, clsname, oldcontents)
    if newcontents != oldcontents:
        if backup and oldcontents != '':
            backup_file(file)
        file_dir = os.path.split(file)[0]
        if not os.path.isdir(file_dir):
            make_dir(file_dir)
        write_file(file, newcontents)
        return True

    return False


# test the module
if __name__ == "__main__":
    import sys

    # verify that the correct number of command-line arguments are provided
    if len(sys.argv) < 4:
        sys.stderr.write('Usage: '+sys.argv[0]+' <infile> <classname> <existing_impl>')
        sys.exit()

    # create the header object
    header = obj_header()
    header.add_file(sys.argv[1])

    # read the existing implementation file into memory
    try:
        f = open(sys.argv[3], 'r')
        data = f.read()
    except IOError, (errno, strerror):
        raise Exception('Failed to read file '+sys.argv[3]+': '+strerror)
    else:
        f.close()

    # dump the result to stdout
    sys.stdout.write(make_ctocpp_class_impl(header, sys.argv[2], data))