The following example runs hcidump on a child thread.  This happens to be a bluetooth bluez tool which continuously outputs events as it seens them. This code allows this to happen on a child thread with the output passed back to the main application thread using a named pipe.

Create the pipe and the child thread process

#include <iostream>
#include <fcntl.h>
#include <unistd.h>

int our_input_fifo_filestream = -1;

	//--------------------------------------
	//----- CREATE A FIFO / NAMED PIPE -----
	//--------------------------------------
	int result;

	printf("Making FIFO...\n");
	result = mkfifo(OUR_INPUT_FIFO_NAME, 0777);		//(This will fail if the fifo already exists in the system from the app previously running, this is fine)
	if (result == 0)
	{
		//FIFO CREATED
		printf("New FIFO created: %s\n", OUR_INPUT_FIFO_NAME);
	}

	printf("Process %d opening FIFO %s\n", getpid(), OUR_INPUT_FIFO_NAME);
	our_input_fifo_filestream = open(OUR_INPUT_FIFO_NAME, (O_RDONLY | O_NONBLOCK));
					//Possible flags:
					//	O_RDONLY - Open for reading only.
					//	O_WRONLY - Open for writing only.
					//	O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
					//											if there is no input immediately available (instead of blocking). Likewise, write requests can also return
					//											immediately with a failure status if the output can't be written immediately.
	if (our_input_fifo_filestream != -1)
		printf("Opened input FIFO: %i\n", our_input_fifo_filestream);


	//----------------------------------------------
	//----- RUN HCIDUMP ON A BACKGROUND THREAD -----
	//----------------------------------------------
	int pid2 = fork();
	if(pid2 == 0)
	{
		//----- THIS IS THE CHILD THREAD -----
		//cout << "I am the child" << endl;

		FILE* pipe2 = popen("sudo hcidump", "r");		//Send the command, popen exits immediately 
		if (pipe2)
		{
			//----- THIS CHILD THREAD WILL RUN FOREVER -----
			cout << "Bluetooth hcidump child thread started" << endl;

			//Create an output filestream for this child thread
			int our_output_fifo_filestream = -1;
			our_output_fifo_filestream = open(OUR_INPUT_FIFO_NAME, (O_WRONLY | O_NONBLOCK));
								//Possible flags:
								//	O_RDONLY - Open for reading only.
								//	O_WRONLY - Open for writing only.
								//	O_NDELAY / O_NONBLOCK (same function) - Enables nonblocking mode. When set read requests on the file can return immediately with a failure status
								//											if there is no input immediately available (instead of blocking). Likewise, write requests can also return
								//											immediately with a failure status if the output can't be written immediately.
			if (our_output_fifo_filestream != -1)
				cout << "Opened output FIFO: " << our_output_fifo_filestream << endl;

			char buffer2[128];
			while(!feof(pipe2))						//Wait for the output resulting from the command
			{
				if(fgets(buffer2, 128, pipe2) != NULL)
				{
					write(our_output_fifo_filestream, (void*)buffer2, strlen(buffer2));	
					//cout << buffer2 << endl;
				}
			}
			cout << "Bluetooth hcidump child thread ending" << endl;
			pclose(pipe2);
		}
		_exit(0);		//Don't forget to exit!
	}
	else
	{
		//cout << "I am the parent\n" << endl;
		wait();		//Optional if you want to wait on the child thread, remove if not
	}

Reading the output from the main application thread

	//---------------------------------------------
	//----- CHECK FIFO FOR ANY RECEIVED BYTES -----
	//---------------------------------------------
	// Read up to 255 characters from the port if they are there
	if (our_input_fifo_filestream != -1)
	{
		unsigned char buffer3[256];
		int length3 = read(our_input_fifo_filestream, (void*)buffer3, 255);		//Filestream, buffer to store in, number of bytes to read (max)
		if (length3 < 0)
		{
			//An error occured (this can happen)
		}
		else if (length3 == 0)
		{
			//No data waiting
		}
		else
		{
			//Bytes received
			buffer3[length3] = '\0';
			cout << buffer3 << endl;
		}
	}