Writing input stream with source - novalexei/nstream GitHub Wiki

Writing input stream with source.

In order to write your own intput stream with nova::stream you'll need to write source class. The source class has the following requirements:

It should have type definitions for character type and for category (which in this case is always source):

typedef source                 category;
typedef /* character type */   char_type;

It should implement the following method:

std::streamsize read(char_type* s, std::streamsize n);

Method read reads from the underlying stream into buffer s up to n characters and returns the actual number of characters read.

Example

Let's write simple replacement for std::istringstream

#include <nova/io.h>

using namespace nova;

template<typename CharT>
class string_source
{
public:
    typedef source                   category;

    typedef CharT                    char_type;
    typedef std::basic_string<CharT> string_type;

    explicit string_source(string_type str) : _buffer{std::move(str)} {}

    std::streamsize read(char_type* s, std::streamsize n)
    {
        if (ptr >= _buffer.size()) return 0;
        std::streamsize toWrite = n < _buffer.size() - ptr ? n : _buffer.size() - ptr;
        std::copy(_buffer.data()+ptr, _buffer.data()+ptr+toWrite, s);
        ptr += toWrite;
        return toWrite;
    }
private:
    const string_type _buffer;
    typename string_type::size_type ptr = 0;
};

And here is how it can be used:

int main()
{
    std::string s{"123 456"};
    instream<string_source<char>> in{s};
    int i1, i2;
    in >> i1 >> i2;
    std::cout << i1 << " " << i2 << std::endl;
    return 0;
}

Buffering

By default nova::instream is unbuffered. Template class nova::instream accepts buffering info class as a second template argument. For example if we want to have 1Kb buffer we can create the object as follows:

instream<string_source<char>, buffering<1024>> in{s};

instream<string_source<char>, buffer_1k> in{s};

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Writing input stream with source - novalexei/nstream GitHub Wiki