C++ ring Buffer

[minusnoob]

I am wondering if anyone have some tips to how I can make a ring buffer in c++. It's need to be able to store strings.

This is really important to me so all kinds of help is very appreciated.
Tips, tutorials, and whatnot.

[LB]

Just use Boost: http://www.boost.org/doc/libs/1_59_0/doc/html/circular_buffer.html

[minusnoob]

I'd rather make it myself but I can barrely find anything. I might have to go with that, so I thank you for the link anyway.

[LB]

Why would you prefer to make it yourself? The point of programming is to write less code, not more. I could understand wanting to learn how they work, but if you intend to actually use it in your code, you should use a more well-tested and expertly designed existing library rather than something you made yourself and think might work. I wouldn't even trust myself to create a working circular buffer.

[minusnoob]

Well, I want to make it myself for my project. I have installed the btw, but I would still make it myself, but the internet is so empty on this subject.

[JLBorges]

Would it be a fixed capacity ring buffer (eg. store up to a maximum of 1000 strings) or a resizeable capacity ring buffer?

[minusnoob]

A fixed would be great, because I am also going to make some threads that can write to and from this buffer.

[JLBorges]

The general idea would be something along these lines
(caveat: incomplete, not thread-safe, not the most efficient, untested etc.):

#include <iostream>
#include <string>
#include <vector>

struct ring_buffer
{
    ring_buffer( std::size_t cap ) : buffer(cap) {}
    bool empty() const { return sz == 0 ; }
    bool full() const { return sz == buffer.size() ; }

    void push( std::string str )
    {
        if( last >= buffer.size() ) last = 0 ;
        buffer[last] = str ;
        ++last ;
        if( full() ) first = (first+1) %  buffer.size() ;
        else ++sz ;
    }

    std::string& operator[] ( std::size_t pos )
    {
        auto p = ( first + pos ) % buffer.size() ;
        return buffer[p] ;
    }

    std::ostream& print( std::ostream& stm = std::cout ) const
    {
        if( first < last )
            for( std::size_t i = first ; i < last ; ++i ) std::cout << buffer[i] << ' ' ;
        else
        {
            for( std::size_t i = first ; i < buffer.size() ; ++i ) std::cout << buffer[i] << ' ' ;
            for( std::size_t i = 0 ; i < last ; ++i ) std::cout << buffer[i] << ' ' ;
        }
        return stm ;
    }

    private:
        std::vector<std::string> buffer ;
        std::size_t first = 0 ;
        std::size_t last = 0 ;
        std::size_t sz = 0 ;
};

int main()
{
    ring_buffer rb(8) ;

    for( int i = 10 ; i < 30 ; ++i )
    {
        rb.push( std::to_string(i) ) ;
        rb.print() << '\n' ;
    }
}

http://coliru.stacked-crooked.com/a/f940bac04da42b86

[minusnoob]

Thank you very much for this. You definetly have some more programming experience than me. Could you explain a couple of sentences for me?

ring_buffer( std::size_t cap ) : buffer(cap) {}

Is there another way to write this sentence? The sentence above.

auto p = ( first + pos ) % buffer.size() ;

I have also never seen the auto keyword.

I am not especially familiar with these either
bool empty() const { return sz == 0 ; }
bool full() const { return sz == buffer.size() ; }

But I think I can figure out that by myself. Just by printing out I can see that it's not working exactly as supposed but I am trying to fix that.

[JLBorges]

> ring_buffer( std::size_t cap ) : buffer(cap) {}

Initialise the buffer to hold 'cap' empty strings.
Constructor (3) http://en.cppreference.com/w/cpp/container/vector/vector

Another way to write it: ring_buffer( std::size_t cap ) { buffer.resize(cap) ; }
http://en.cppreference.com/w/cpp/container/vector/resize


> auto p = ( first + pos ) % buffer.size() ;

auto: http://www.stroustrup.com/C++11FAQ.html#auto

Another way to write it: std::size_t p = ( first + pos ) % buffer.size() ;


Perhaps you should read a tutorial on vectors: https://cal-linux.com/tutorials/vectors.html