handle_errors.c

Handling errors returned from the library.

#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);
}