Add an example of proper error handling.

examples/.gitignore

@@ -1,3 +1,4 @@
+handle_errors
 list_ports
 port_info
 port_config

examples/handle_errors.c

@@ -0,0 +1,116 @@
+#include <libserialport.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* Example of how to handle errors from libserialport.
+ *
+ * This example file is released to the public domain. */
+
+/* Pointers used in the program to resources that may need to be freed. */
+struct sp_port **port_list = NULL;
+struct sp_port_config *config = NULL;
+struct sp_port *port = NULL;
+
+/* Example of a function to clean up and exit the program with a given return code. */
+void end_program(int return_code)
+{
+	/* Free any structures we allocated. */
+	if (port_list != NULL)
+		sp_free_port_list(port_list);
+	if (config != NULL)
+		sp_free_config(config);
+	if (port != NULL)
+		sp_free_port(port);
+
+	/* Exit with the given return code. */
+	exit(return_code);
+}
+
+/* Example of a helper function for error handling. */
+int check(enum sp_return result)
+{
+	int error_code;
+	char *error_message;
+	switch (result) {
+
+		/* Handle each of the four negative error codes that can be returned.
+		 *
+		 * In this example, we will end the program on any error, using
+		 * a different return code for each possible class of error. */
+
+		case SP_ERR_ARG:
+			/* When SP_ERR_ARG is returned, there was a problem with one
+			 * or more of the arguments passed to the function, e.g. a null
+			 * pointer or an invalid value. This generally implies a bug in
+			 * the calling code. */
+			printf("Error: Invalid argument.\n");
+			end_program(1);
+
+		case SP_ERR_FAIL:
+			/* When SP_ERR_FAIL is returned, there was an error from the OS,
+			 * which we can obtain the error code and message for. These
+			 * calls must be made in the same thread as the call that
+			 * returned SP_ERR_FAIL, and before any other system functions
+			 * are called in that thread, or they may not return the
+			 * correct results. */
+			error_code = sp_last_error_code();
+			error_message = sp_last_error_message();
+			printf("Error: Failed: OS error code: %d, message: '%s'\n",
+				error_code, error_message);
+			/* The error message should be freed after use. */
+			sp_free_error_message(error_message);
+			end_program(2);
+
+		case SP_ERR_SUPP:
+			/* When SP_ERR_SUPP is returned, the function was asked to do
+			 * something that isn't supported by the current OS or device,
+			 * or that libserialport doesn't know how to do in the current
+			 * version. */
+			printf("Error: Not supported.\n");
+			end_program(3);
+
+		case SP_ERR_MEM:
+			/* When SP_ERR_MEM is returned, libserialport wasn't able to
+			 * allocate some memory it needed. Since the library doesn't
+			 * normally use any large data structures, this probably means
+			 * the system is critically low on memory and recovery will
+			 * require very careful handling. The library itself will
+			 * always try to handle any allocation failure safely.
+			 *
+			 * In this example, we'll just try to exit gracefully without
+			 * calling printf, which might need to allocate further memory. */
+			end_program(4);
+
+		case SP_OK:
+		default:
+			/* A return value of SP_OK, defined as zero, means that the
+			 * operation succeeded. */
+			printf("Operation succeeded.\n");
+
+			/* Some fuctions can also return a value greater than zero to
+			 * indicate a numeric result, such as the number of bytes read by
+			 * sp_blocking_read(). So when writing an error handling wrapper
+			 * function like this one, it's helpful to return the result so
+			 * that it can be used. */
+			return result;
+	}
+}
+
+int main(int argc, char **argv)
+{
+	/* Call some functions that should not result in errors. */
+
+	printf("Getting list of ports.\n");
+	check(sp_list_ports(&port_list));
+
+	printf("Creating a new port configuration.\n");
+	check(sp_new_config(&config));
+
+	/* Now make a function call that will result in an error. */
+
+	printf("Trying to find a port that doesn't exist.\n");
+	check(sp_get_port_by_name("NON-EXISTENT-PORT", &port));
+
+	/* We could now clean up and exit normally if an error hadn't occured. */
+	end_program(0);
+}