Add example of sending and receiving data.

examples/.gitignore

@@ -3,3 +3,4 @@ handle_errors
 list_ports
 port_info
 port_config
+send_receive

examples/send_receive.c

@@ -0,0 +1,136 @@
+#include <libserialport.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Example of how to send and receive data.
+ *
+ * This example file is released to the public domain. */
+
+/* Helper function for error handling. */
+int check(enum sp_return result);
+
+int main(int argc, char **argv)
+{
+	/* This example can be used with one or two ports. With one port, it
+	 * will send data and try to receive it on the same port. This can be
+	 * done by connecting a single wire between the TX and RX pins of the
+	 * port.
+	 *
+	 * Alternatively it can be used with two serial ports connected to each
+	 * other, so that data can be sent on one and received on the other.
+	 * This can be done with two ports with TX/RX cross-connected, e.g. by
+	 * a "null modem" cable, or with a pair of interconnected virtual ports,
+	 * such as those created by com0com on Windows or tty0tty on Linux. */
+
+	/* Get the port names from the command line. */
+	if (argc < 2 || argc > 3) {
+		printf("Usage: %s <port 1> [<port 2>]\n", argv[0]);
+		return -1;
+	}
+	int num_ports = argc - 1;
+	char **port_names = argv + 1;
+
+	/* The ports we will use. */
+	struct sp_port *ports[2];
+
+	/* Open and configure each port. */
+	for (int i = 0; i < num_ports; i++) {
+		printf("Looking for port %s.\n", port_names[i]);
+		check(sp_get_port_by_name(port_names[i], &ports[i]));
+
+		printf("Opening port.\n");
+		check(sp_open(ports[i], SP_MODE_READ_WRITE));
+
+		printf("Setting port to 9600 8N1, no flow control.\n");
+		check(sp_set_baudrate(ports[i], 9600));
+		check(sp_set_bits(ports[i], 8));
+		check(sp_set_parity(ports[i], SP_PARITY_NONE));
+		check(sp_set_stopbits(ports[i], 1));
+		check(sp_set_flowcontrol(ports[i], SP_FLOWCONTROL_NONE));
+	}
+
+	/* Now send some data on each port and receive it back. */
+	for (int tx = 0; tx < num_ports; tx++) {
+		/* Get the ports to send and receive on. */
+		int rx = num_ports == 1 ? 0 : ((tx == 0) ? 1 : 0);
+		struct sp_port *tx_port = ports[tx];
+		struct sp_port *rx_port = ports[rx];
+
+		/* The data we will send. */
+		char *data = "Hello!";
+		int size = strlen(data);
+
+		/* We'll allow a 1 second timeout for send and receive. */
+		unsigned int timeout = 1000;
+
+		/* On success, sp_blocking_write() and sp_blocking_read()
+		 * return the number of bytes sent/received before the
+		 * timeout expired. We'll store that result here. */
+		int result;
+
+		/* Send data. */
+		printf("Sending '%s' (%d bytes) on port %s.\n",
+				data, size, sp_get_port_name(tx_port));
+		result = check(sp_blocking_write(tx_port, data, size, timeout));
+
+		/* Check whether we sent all of the data. */
+		if (result == size)
+			printf("Sent %d bytes successfully.\n", size);
+		else
+			printf("Timed out, %d/%d bytes sent.\n", result, size);
+
+		/* Allocate a buffer to receive data. */
+		char buf[size + 1];
+
+		/* Try to receive the data on the other port. */
+		printf("Receiving %d bytes on port %s.\n",
+				size, sp_get_port_name(rx_port));
+		check(sp_blocking_read(rx_port, buf, size, timeout));
+
+		/* Check whether we received the number of bytes we wanted. */
+		if (result == size)
+			printf("Received %d bytes successfully.\n", size);
+		else
+			printf("Timed out, %d/%d bytes received.\n", result, size);
+
+		/* Check if we received the same data we sent. */
+		buf[result] = '\0';
+		printf("Received '%s'.\n", buf);
+	}
+
+	/* Close ports and free resources. */
+	for (int i = 0; i < num_ports; i++) {
+		check(sp_close(ports[i]));
+		sp_free_port(ports[i]);
+	}
+
+	return 0;
+}
+
+/* Helper function for error handling. */
+int check(enum sp_return result)
+{
+	/* For this example we'll just exit on any error by calling abort(). */
+	char *error_message;
+
+	switch (result) {
+	case SP_ERR_ARG:
+		printf("Error: Invalid argument.\n");
+		abort();
+	case SP_ERR_FAIL:
+		error_message = sp_last_error_message();
+		printf("Error: Failed: %s\n", error_message);
+		sp_free_error_message(error_message);
+		abort();
+	case SP_ERR_SUPP:
+		printf("Error: Not supported.\n");
+		abort();
+	case SP_ERR_MEM:
+		printf("Error: Couldn't allocate memory.\n");
+		abort();
+	case SP_OK:
+	default:
+		return result;
+	}
+}

libserialport.h

@@ -68,6 +68,7 @@
  * - @ref list_ports.c - Getting a list of ports present on the system.
  * - @ref port_info.c - Getting information on a particular serial port.
  * - @ref port_config.c - Accessing configuration settings of a port.
+ * - @ref send_receive.c - Sending and receiving data.
  * - @ref await_events.c - Awaiting events on multiple ports.
  * - @ref handle_errors.c - Handling errors returned from the library.
  *
@@ -1289,6 +1290,8 @@ SP_API enum sp_return sp_set_flowcontrol(struct sp_port *port, enum sp_flowcontr
  *
  * Reading, writing, and flushing data.
  *
+ * See @ref send_receive.c for an example of sending and receiving data.
+ *
  * @{
  */
 
@@ -1812,6 +1815,7 @@ SP_API const char *sp_get_lib_version_string(void);
  * @example list_ports.c Getting a list of ports present on the system.
  * @example port_info.c Getting information on a particular serial port.
  * @example port_config.c Accessing configuration settings of a port.
+ * @example send_receive.c Sending and receiving data.
  * @example await_events.c - Awaiting events on multiple ports.
  * @example handle_errors.c - Handling errors returned from the library.
 */