I am looking for some simple and efficient parameter container that would act like a in-memory-xml file representation (or ini-file, as another sample).
I mean, basically it could store sections and sets of parameters for each section, have easy accessors like GetValue("ParameterName") and simple return value casting.
It would be great if it is serializable.
I wrote something like that yesterday and, well, it suits my needs, but probably there is something more convenient and flexible available?
Maybe some kind of parameter map in boost?
Thank you
Take a look at boost::program_options. It does what you want and more: INI file parsing, environment variables parsing, commandline options parsing and extensibility.
Have you considered std::map<>?
Dunno if it's overkill or not, but the Message class in MUSCLE does all of the things you listed above. You can use it to serialize any kind of data (structured or not), or use it as an in-memory container for parsed .ini style config files via ParseFile()/UnparseFile().
You can use Boost.PropertyTree.
It reads and writes xml and ini files.
It stores the parameters as a tree and you can use dot notation to access the values:
std::string value = pt.get<std::string>("debug.filename");
You can also insert new values using:
pt.put("debug.filename", fileName);
Related
I have a configuration file, that is a json. I have created a class (ConfigFile) that reads that file and store the values (using boost parser and ptree). I am wandering is it a good practice to use the ptree as a member of the ConfigFile class, or I shall use it just for reading the json and store the values in a map member?
I'd say what matters is the ConfigFile's interface. If you can keep it consistent with either version, it shouldn't be a problem to just choose one and switch to the other if you feel the need without breaking anything.
Keep property tree out of the header. The latter can also be fixed with the pimpl idiom.
#sehe's comment makes a lot of sense here as well and is something to remember.
I'm asking here because i have already tried to search but i have no idea if this things even exist and what their names are.
I start explaining that with custom pattern i mean this: suppose that i need to serialize objects or data of type foo, bar and boo, usually the library handle this for the user in a very simple way, what comes first goes in first in the serialization process, so if i serialize all the foo first they are written "at the top" of the file and all the bar and boo are after the foo.
Now I would like to keep order in my file and organize things based on a custom pattern, it's this possible with Boost ? What section provides this feature ?
Second thing, that is strictly related to the first one, I also would like to access my serialized binary files in a way that I'm not forced to parse and read all the previous values to extract only the one that I'm interested in, kinda like the RAM that works based on memory address and offers a random access without forcing you to parse all the others addresses.
Thanks.
On the first issue: the Boost serialization library is agnostic as to what happens after it turns an object into its serialized form. It does this by using input and output streams. Files are just that - fostream/fistream. For other types of streams however, the order/pattern that you speak of doesn't make sense. Imagine you're sending serialized objects over the network - the library can't know that it'll have to rearrange the order of objects and, in fact, it can't do that once they've been sent. For this reason, it does not support what you're looking for.
What you can do is create a wrapper that either just caches serialized versions of the objects and arranges them in memory before you tell it to write them out to a file, or that knows that since you're working with files, it can later tellg to the appropriate place in the file and append (this approach would require you to store the locations of the objects you wrote to the file).
As for the second thing - random access file reading. You will have to know exactly where the object is in memory. If you know that the structure of your file won't change, you can seekg on the file stream before handing it to boost for deserialization. If the file structure will change however, you still need to know the location of objects in the file. If you don't want to parse the file to find it, you'll have to store it somewhere during serialization. For example - you can maintain a sort of registry of objects at the top of the file. You will still have to parse it, but it should be just a simple [Object identifier]-[location in file] sort of thing.
I have a query, I have set of flat files ( say file1, file2 etc) containing column names and native data types. ( how values are stored and can be read in c++ is elementary)
eg. flat file file1 may have data like
col1_name=id, col1_type=integer, col2_name=Name, col2_type=string and so on.
So for each flat file I need to create C++ data structure ( i.e 1 flat file = 1 data structure) where the member variable name is same name as column name and its data type will be of C++ native data type like int, float, string etc. according to column type in flat file.
from above eg: my flat file 1 should give me below declaration
class file1{
int id;
string Name;
};
Is there a way I can write code in C++, where binary once created will read the flat file and create data structure based on the file ( class name will be same as flat file name). All the classes created using these flat files will have common functionality of getter and setter member functions.
Do let me know if you have done something similar earlier or have any idea for this.
No, not easily (see the other answers for reasons why not).
I would suggest having a look at Python instead for this kind of problem. Python's type system combined with its ethos of using try/except lends itself more easily to the challenge of parsing data.
If you really must use C++, then you might find a solution using the dynamic properties feature of Qt's QObject class, combined with the QVariant class. Although this would do what you want, I would add a warning that this is getting kind of heavy-weight and may over-complicate your task.
No, not directly. C++ is a compiled language. The code for every class is created by the compiler.
You would need a two-step process. First, write a program that reads those files and translates them into a .cpp file. Second, pass those .cpp files to a compiler.
C++ classes are pure compile-time concepts and have no meaning at runtime, so they cannot be created. However, you could just go with
std::vector<std::string> fields;
and parse as necessary in your accessor functions.
No, but from what I can tell, you have to be able to store the names of multiple columns. What you can do is have a member variable map or unordered_map which you can index with a string - the name of the column - and get some data (like a column object or something) back. That way you can do
obj.Columns["Name"]
I'm not sure there's a design pattern to this, but if your list of possible type names is finite, and known at compile time, can't you declare all those classes in your program before running, and then just instantiate them based on the data in the files?
What you actually want is a field whose exact nature varies at runtime.
There are several approaches, including Boost.Any, but because of the static nature of C++ type system only 2 are really recommended, and both require to have beforehand an idea of all the possible data types that may be required.
The first approach is typical:
Object base type
Int, String, Date whatever derived types
and the use of polymorphism.
The second requires a bit of Boost magic: boost::variant<int, std::string, date>.
Once you have the "variant" part covered, you need to implement visitation to distinguish between the different possible types. Typical visitors for the traditional object-oriented approach or simply boost::static_visitor<> and boost::apply_visitor combinations for the boost approach.
It's fairly straightforward.
Is there something like a class that might be used to store Files and directories in, just like the way Zip files might be used?
Since I haven't found any "real" class to write Zip files (real class as in real class),
It would be nice to be able to store Files and Directories in a container-like file.
A perfect API would probably look like this:
int main()
{
ContainerFile cntf("myContainer.cnt", ContainerFile::CREATE);
cntf.addFile("data/some-interesting-stuff.txt");
cntf.addDirectory("data/foo/");
cntf.addDirectory("data/bar/", ContainerFile::RECURSIVE);
cntf.close();
}
... I hope you get the Idea.
Important Requirements are:
The Library must be crossplatform
anything *GPL is not acceptable in this case (MIT and BSD License are)
I already played with the thought of creating an Implentation based on SQLite (and its ability to store binary blobs). Unfortunately, it seems impossible to store Directory structures in a SQLite Database, which makes it pretty much useless in this case.
Is it useless to hope for such a class library?
In an SQLite db you can store directory-like structures... you just have to have a "Directories" table, with one entry for each directory, having at least an index and a "parent" field (which holds the index of another directory, or 0 if it has no parent). Then you can have a "Files" table, which contains file attributes, the index of the parent directory and the file content.
That's it, now you have your directory tree in a relational DB.
Someone pointed me to PhysicsFS, which has an API similar to what you describe, but it's a pure C API that does everything you need. A trivial object-oriented wrapper could be easily written.
You might like to check out http://www.cs.unc.edu/Research/compgeom/gzstream/
If you are making your own then redis may be a better choice than SQLite as I believe it handles binary data better.
I took the time to write a tiny, yet working wrapper around libarchive. I'm not exactly familiar with all features of Libarchive, but the result fits what I needed:
archive_wrapper.cpp # gist.github.com
It uses libmars for strings, etc. But I guess it wouldn't be too hard to replace the mars::mstring occurances with std::string.
And of course this wrapper is available under the MIT/X11 License (just as libmars), which means you can do whatever you want with it. ;-)
In my job, i need to parse different kind of data files from different data sources.Sometimes i parse them by writing directly c++ code (with the help of qt and boost:D), sometimes manually with a helper program.
I must note that data types are so different from each other it is so hard to create common a interface for all of them. But i want to do this job in a more generic way.I am planning to write a library to convert them and it should be easy to add new parser utility in future.I am also planning to use other helper programs inside my program, not manually.
My question is what kind of an architecture or pattern do you suggest, Basic condition is library must be extendable via new classes or dll's and also configurable.
By the way data can be in text, ascii or something like CSV(comma seperated values) and most of them are specific for a certain data.
Not to blow my own trumpet, but my small Open Source utility CSVfix has an extensible architecture based on deriving new C++ classes with a very simple interface. I did consider using a plugin-architecture with DLLs but it seemed like overkill for such a simple utility . If interested, you can get the binaries & sources here.
I'd suggest a 3-part model, where the common data-format is a String which should be able to contain every value:
Reader: In this layer the values are read from the source (ie. CSV-file) using some sort of file-format-descriptor. The values are then stored in some sort of intermediate data structure.
Connector/Converter: This layer is responsible for mapping the reader-data to the writer-fields.
Writer: This layer is responsible for writing a specific data structure to the target (ie. another file-format or a database).
This way you can write different Readers for different input files.
I think the hardest part would be creating the definition of the intermediate storage format/structure so that it is future-proof and flexible.
One method I used for defining data structure in my datafile read/write classes is to use std::map<std::string, std::vector<std::string>, string_compare> where the key is the variable name and the vector of strings is the data. While this is expensive in memory, it does not lock me down to only numeric data. And, this method allows for different lengths of data within the same file.
I had the base class implement this generic storage, while the derived classes implemented the reader/writer capability. I then used a factory to get to the desired handler, using another class that determined the file format.