async_read on async_pipe child process giving no data - c++

Question

I have the following code which is simplified from my real code where I am trying to do an async_read on an async_pipe connected to a child process. In the child process I am calling "ls ." as just a test and I want my async read to get the result of that. It returns the following
$ ./a.out
system:0
0
Why does this happen I cannot figure out? Ideally I want to replace "ls ." with a long running process where I can read line after line with async_read.
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <iostream>
#include <fstream>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <boost/process.hpp>
namespace bp = boost::process;
class test {
private:
boost::asio::io_service ios;
boost::asio::io_service::work work;
bp::async_pipe ap;
std::vector<char> buf;
public:
test()
: ios(), work(ios), ap(ios) {
}
void read(
const boost::system::error_code& ec,
std::size_t size) {
std::cout << ec << std::endl;
std::cout << size << std::endl;
}
void run() {
bp::child c(bp::search_path("ls"), ".", bp::std_out > ap);
boost::asio::async_read(ap, boost::asio::buffer(buf),
boost::bind(&test::read,
this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
ios.run();
}
};
int main() {
test c;
c.run();
}

Answer 1

You read into a vector of size 0.
You read 0 bytes. That's what you asked for.
I'd suggest using a streambuf and just reading till EOF. Also, drop work unless you really did want run() to never return:
Live On Coliru
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/process.hpp>
#include <iostream>
namespace bp = boost::process;
class test {
private:
boost::asio::io_service ios;
bp::async_pipe ap;
boost::asio::streambuf buf;
public:
test() : ios(), ap(ios) {}
void read(const boost::system::error_code &ec, std::size_t size) {
std::cout << ec.message() << "\n";
std::cout << size << "\n";
std::cout << &buf << std::flush;
}
void run() {
bp::child c(bp::search_path("ls"), ".", bp::std_out > ap, ios);
async_read(ap, buf, boost::bind(&test::read, this, _1, _2));
ios.run();
}
};
int main() {
test c;
c.run();
}
Prints, e.g.
End of file
15
a.out
main.cpp