RtMidiライブラリを使って、MIDIインターフェースを作成する ref: https://qiita.com/ixsiid/items/dfd093732d05260ed174

create_midi_interface.cpp

#include <iostream>
#include "midi.hpp"

int main () {
    MidiInterface * p = new MidiInterface("foobar");
    p->connect("Midi Through", MidiDirection::OUT);
    while (true) std::cin.getc();
    exit(0);
}

file0.txt

> aconnect -l
client 0: 'System' [type=kernel]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=kernel]
    0 'Midi Through Port-0'

file4.txt

$ aconnect -l
client 0: 'System' [type=kernel]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=kernel]
    0 'Midi Through Port-0'
$ ./create_midi_interface.o &
$ aconnect -l
client 0: 'System' [type=kernel]
    0 'Timer           '
    1 'Announce        '
client 14: 'Midi Through' [type=kernel]
    0 'Midi Through Port-0'
        Connected From: 128:0[real:0]
client 128: 'foobar Midi Output Client' [type=user,pid=1528]
    0 'foobar Midi Output Port'
        Connecting To: 14:0[real:0]

midi.cpp

#include "midi.hpp"


MidiInterface::MidiInterface(const char * interfaceName) {
    name = interfaceName;
}

RtMidi * MidiInterface::connect(std::string target, MidiDirection direction) {
    char clientName[256] = "";
    sprintf(clientName, "%s Midi %s Client", name, direction == MidiDirection::IN ? "Input" : "Output");
    RtMidi * midi = direction == MidiDirection::IN ? 
        (RtMidi *)new RtMidiIn (RtMidi::UNSPECIFIED, clientName) :
        (RtMidi *)new RtMidiOut(RtMidi::UNSPECIFIED, clientName);

    unsigned int portCount = midi->getPortCount();
    for (unsigned int i=0; i<portCount; i++) {
        std::string portName = midi->getPortName(i).c_str();
        std::string::size_type index = portName.find(target, 0);
        if (index != std::string::npos) {
            char portName[256] = "";
            sprintf(portName, "%s Midi %s Port", name, direction == MidiDirection::IN ? "Input" : "Output");
            midi->openPort(i, portName);
            return midi;
        }
    }
    return NULL;
}

midi.hpp

#include <iostream>
#include "RtMidi.h"

enum struct MidiDirection {
    IN,
    OUT,
};

class MidiInterface {
private:
    const char * name;
public:
    MidiInterface(const char * interfaceName);
    RtMidi * connect(std::string target, MidiDirection direction);
};