This page describes the C++ code generator and demonstrates how to use a Freeze map in a C++ program.
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slice2freeze Command-Line Options
The Slice-to-Freeze compiler, slice2freeze, creates C++ classes for Freeze maps. The compiler offers the following command-line options in addition to the standard options:
--header-ext EXT
Changes the file extension for the generated header files from the default h to the extension specified by EXT.
--source-ext EXT
Changes the file extension for the generated source files from the default cpp to the extension specified by EXT.
--add-header HDR[,GUARD]
This option adds an include directive for the specified header at the beginning of the generated source file (preceding any other include directives). If GUARD is specified, the include directive is protected by the specified guard.
For example:
--add-header precompiled.h,_PRECOMPILED_H__
results in the following directives at the beginning of the generated source file:
#ifndef __PRECOMPILED_H__ #define __PRECOMPILED_H__ #include <precompiled.h> #endif
As this example demonstrates, the --add-header option is useful mainly for integrating the generated code with a compiler's precompiled header mechanism.
This option can be repeated to create include directives for several files.
--include-dir DIR
Modifies #include directives in source files to prepend the path name of each header file with the directory DIR. The discussion of slice2cpp provides more information.
--dll-export SYMBOL
Use SYMBOL to control DLL exports or imports. See the slice2cpp description for details.
--dict NAME,KEY,VALUE[,sort[,COMPARE]]
Generate a Freeze map class named NAME using KEY as key and VALUE as value. This option may be specified multiple times to generate several Freeze maps. NAME may be a scoped C++ name, such as Demo::Struct1ObjectMap. KEY and VALUE represent Slice types and therefore must use Slice syntax, such as bool or Ice::Identity. The type identified by KEY must be a legal dictionary key type. By default, keys are sorted using their binary Ice-encoded representation. Include sort to sort with the COMPARE functor class. If COMPARE is not specified, the default value is std::less<KEY>.
--dict-index MAP[,MEMBER] [,case-sensitive|case-insensitive][,sort[,COMPARE]]
Add an index to the Freeze map named MAP. If MEMBER is specified, the map value type must be a structure or a class, and MEMBER must be a member of this structure or class. Otherwise, the entire value is indexed. When the indexed member (or entire value) is a string, the index can be case-sensitive (default) or case-insensitive. An index adds additional member functions to the generated C++ map:
iterator findByMEMBER(MEMBER_TYPE, bool = true);const_iterator findByMEMBER(MEMBER_TYPE,bool = true) const;iterator beginForMEMBER();const_iterator begin_ForMEMBER() const;iterator endForMEMBER();const_iterator endForMEMBER() const;iterator lowerBoundForMEMBER(MEMBER_TYPE);const_iterator lowerBoundForMEMBER(MEMBER_TYPE) const;iterator upperBoundForMEMBER(MEMBER_TYPE);const_iterator upperBoundForMEMBER(MEMBER_TYPE) const;std::pair<iterator, iterator> equalRangeForMEMBER(MEMBER_TYPE);std::pair<const_iterator, const_iterator> equalRangeForMEMBER(MEMBER_TYPE) const;int MEMBERCount(MEMBER_TYPE) const;
When MEMBER is not specified, these functions are findByValue (const and non-const), lowerBoundForValue (const and non-const), valueCount, and so on. When MEMBER is specified, its first letter is capitalized in the findBy function name. MEMBER_TYPE corresponds to an in-parameter of the type of MEMBER (or the type of the value when MEMBER is not specified). For example, if MEMBER is a string, MEMBER_TYPE is a const std::string&.
By default, keys are sorted using their binary Ice-encoded representation. Include sort to sort with the COMPARE functor class. If COMPARE is not specified, the default value is std::less<MEMBER_TYPE>.
findByMEMBER returns an iterator to the first element in the Freeze map that matches the given index value. It returns end() if there is no match. When the second parameter is true (the default), the returned iterator provides only the elements with an exact match (and then skips to end()). Otherwise, the returned iterator sets a starting position and then provides all elements until the end of the map, sorted according to the index comparator.
lowerBoundForMEMBER returns an iterator to the first element in the Freeze map whose index value is not less than the given index value. It returns end() if there is no such element. The returned iterator provides all elements until the end of the map, sorted according to the index comparator.
upperBoundForMEMBER returns an iterator to the first element in the Freeze map whose index value is greater than the given index value. It returns end() if there is no such element. The returned iterator provides all elements until the end of the map, sorted according to the index comparator.
beginForMEMBER returns an iterator to the first element in the map.
endForMEMBER returns an iterator to the last element in the map.
equalRangeForMEMBER returns a range (pair of iterators) of all the elements whose index value matches the given index value. This function is similar to findByMEMBER (see above).
MEMBERCount returns the number of elements in the Freeze map whose index value matches the given index value.
Please note that index-derived iterators do not allow you to set new values in the underlying map.
--index CLASS,TYPE,MEMBER [,case-sensitive|case-insensitive]
Generate an index class for a Freeze evictor. CLASS is the name of the class to be generated. TYPE denotes the type of class to be indexed (objects of different classes are not included in this index). MEMBER is the name of the data member in TYPE to index. When MEMBER has type string, it is possible to specify whether the index is case-sensitive or not. The default is case-sensitive.
Generating a Simple Map for C++
As an example, the following command generates a simple map:
$ slice2freeze --dict StringIntMap,string,int StringIntMap
This command directs the compiler to create a map named StringIntMap, with the Slice key type string and the Slice value type int. The final argument is the base name for the output files, to which the compiler appends the .h and .cpp suffixes. As a result, this command produces two C++ source files, StringIntMap.h and StringIntMap.cpp.
The Freeze Map Class in C++
If you examine the contents of the header file created by the example in the previous section, you will discover that a Freeze map is an instance of the template class Freeze::Map:
// StringIntMap.h typedef Freeze::Map<std::string, Ice::Int, ...> StringIntMap;
The Freeze::Map template class closely resembles the STL container class std::map, as shown in the following class definition:
namespace Freeze {
template<...> class Map {
public:
typedef ... value_type;
typedef ... iterator;
typedef ... const_iterator;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
Map(const Freeze::ConnectionPtr& connection,
const std::string& dbName,
bool createDb = true,
const Compare& compare = Compare());
template<class _InputIterator>
Map(const Freeze::ConnectionPtr& connection,
const std::string& dbName,
bool createDb,
_InputIterator first, _InputIterator last,
const Compare& compare = Compare());
static void recreate(const Freeze::ConnectionPtr& connection,
const std::string& dbName,
const Compare& compare = Compare());
bool operator==(const Map& rhs) const;
bool operator!=(const Map& rhs) const;
void swap(Map& rhs);
iterator begin();
const_iterator begin() const;
iterator end();
const_iterator end() const;
bool empty() const;
size_type size() const;
size_type max_size() const;
iterator insert(iterator /*position*/, const value_type& elem);
std::pair<iterator, bool> insert(const value_type& elem);
template <typename InputIterator>
void insert(InputIterator first, InputIterator last);
void put(const value_type& elem);
template <typename InputIterator>
void put(InputIterator first, InputIterator last);
void erase(iterator position);
size_type erase(const key_type& key);
void erase(iterator first, iterator last);
void clear();
void destroy(); // Non-standard.
iterator find(const key_type& key);
const_iterator find(const key_type& key) const;
size_type count(const key_type& key) const;
iterator lower_bound(const key_type& key);
const_iterator lower_bound(const key_type& key) const;
iterator upper_bound(const key_type& key);
const_iterator upper_bound(const key_type& key) const;
std::pair<iterator, iterator>
equal_range(const key_type& key);
std::pair<const_iterator, const_iterator>
equal_range(const key_type& key) const;
const Ice::CommunicatorPtr&
communicator() const;
...
};
}
The semantics of the Freeze::Map methods are identical to those of std::map unless otherwise noted. In particular, the overloaded insert method shown below ignores the position argument:
iterator insert(iterator /*position*/, const value_type& elem);
A Freeze map class supports only those methods shown above; other features of std::map, such as allocators and overloaded array operators, are not available.
Non-standard methods that are specific to Freeze maps are discussed below:
Constructors
The following overloaded constructors are provided:C++Map(const Freeze::ConnectionPtr& connection, const std::string& dbName, bool createDb = true, const Compare& compare = Compare()); template<class _InputIterator> Map(const Freeze::ConnectionPtr& connection, const std::string& dbName, bool createDb, _InputIterator first, _InputIterator last, const Compare& compare = Compare());
The first constructor accepts a connection, the database name, a flag indicating whether to create the database if it does not exist, and an object used to compare keys. The second constructor accepts all of the parameters of the first, with the addition of iterators from which elements are copied into the map.
Note that a database can only contain the persistent state of one map type. Any attempt to instantiate maps of different types on the same database results in undefined behavior.
Map copy
Therecreatefunction copies an existing database:C++static void recreate(const Freeze::ConnectionPtr& connection, const std::string& dbName, const Compare& compare = Compare())
The
dbNameparameter specifies an existing database name. The copy has the name<dbName>.old-<uuid>. For example, if the database name isMyDB, the copy might be named
MyDB.old-edefd55a-e66a-478d-a77b-f6d53292b873. (Obviously, a different UUID is used each time you recreate a database).
destroy
This method deletes the database from its environment and from the Freeze catalog. If a transaction is not currently open, the method creates its own transaction in which to perform this task.
communicator
This method returns the communicator with which the map's connection is associated.
Using Iterators with Freeze Maps in C++
A Freeze map's iterator works like its counterpart in std::map. The iterator class supports one convenient (but nonstandard) method:
void set(const mapped_type& value)
Using this method, a program can replace the value at the iterator's current position.
Sample Freeze Map Program in C++
The program below demonstrates how to use a StringIntMap to store <string, int> pairs in a database. You will notice that there are no explicit read or write operations called by the program; instead, simply using the map has the side effect of accessing the database.
#include <Freeze/Freeze.h>
#include <StringIntMap.h>
int
main(int argc, char* argv[])
{
// Initialize the Communicator.
//
Ice::CommunicatorPtr communicator = Ice::initialize(argc, argv);
// Create a Freeze database connection.
//
Freeze::ConnectionPtr connection = Freeze::createConnection(communicator, "db");
// Instantiate the map.
//
StringIntMap map(connection, "simple");
// Clear the map.
//
map.clear();
Ice::Int i;
StringIntMap::iterator p;
// Populate the map.
//
for (i = 0; i < 26; i++) {
std::string key(1, 'a' + i);
map.insert(make_pair(key, i));
}
// Iterate over the map and change the values.
//
for (p = map.begin(); p != map.end(); ++p)
p.set(p->second + 1);
// Find and erase the last element.
//
p = map.find("z");
assert(p != map.end());
map.erase(p);
// Clean up.
//
connection->close();
communicator->destroy();
return 0;
}
Prior to instantiating a Freeze map, the application must connect to a Berkeley DB database environment:
Freeze::ConnectionPtr connection = Freeze::createConnection(communicator, "db");
The second argument is the name of a Berkeley DB database environment; by default, this is also the file system directory in which Berkeley DB creates all database and administrative files. Note that properties with the prefix Freeze.DbEnv can modify a number of environment settings, including the file system directory. For the preceding example, you could change the directory to FreezeDir by setting the property Freeze.DbEnv.db.DbHome to FreezeDir.
Next, the code instantiates the StringIntMap on the connection. The constructor's second argument supplies the name of the database file, which by default is created if it does not exist:
StringIntMap map(connection, "simple");
After instantiating the map, we clear it to make sure it is empty in case the program is run more than once:
map.clear();
Next, we populate the map using a single-character string as the key:
for (i = 0; i < 26; i++) {
std::string key(1, 'a' + i);
map.insert(make_pair(key, i));
}
Iterating over the map will look familiar to std::map users. However, to modify a value at the iterator's current position, we use the nonstandard set method:
for (p = map.begin(); p != map.end(); ++p) p.set(p->second + 1);
Next, the program obtains an iterator positioned at the element with key z, and erases it:
p = map.find("z");
assert(p != map.end());
map.erase(p);
Finally, the program closes the database connection:
connection->close();
It is not necessary to explicitly close the database connection, but we demonstrate it here for the sake of completeness.
See Also
- Using the Slice Compilers
- slice2cpp Command-Line Options
- Freeze Evictor Concepts
- Freeze Catalogs
- Freeze Properties