examples/handle_errors.c

   1 #include <libserialport.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4
   5 /* Example of how to handle errors from libserialport.
   6  *
   7  * This example file is released to the public domain. */
   8
   9 /* Pointers used in the program to resources that may need to be freed. */
  10 struct sp_port **port_list = NULL;
  11 struct sp_port_config *config = NULL;
  12 struct sp_port *port = NULL;
  13
  14 /* Example of a function to clean up and exit the program with a given return code. */
  15 void end_program(int return_code)
  16 {
  17         /* Free any structures we allocated. */
  18         if (port_list != NULL)
  19                 sp_free_port_list(port_list);
  20         if (config != NULL)
  21                 sp_free_config(config);
  22         if (port != NULL)
  23                 sp_free_port(port);
  24
  25         /* Exit with the given return code. */
  26         exit(return_code);
  27 }
  28
  29 /* Example of a helper function for error handling. */
  30 int check(enum sp_return result)
  31 {
  32         int error_code;
  33         char *error_message;
  34
  35         switch (result) {
  36
  37                 /* Handle each of the four negative error codes that can be returned.
  38                  *
  39                  * In this example, we will end the program on any error, using
  40                  * a different return code for each possible class of error. */
  41
  42         case SP_ERR_ARG:
  43                 /* When SP_ERR_ARG is returned, there was a problem with one
  44                  * or more of the arguments passed to the function, e.g. a null
  45                  * pointer or an invalid value. This generally implies a bug in
  46                  * the calling code. */
  47                 printf("Error: Invalid argument.\n");
  48                 end_program(1);
  49
  50         case SP_ERR_FAIL:
  51                 /* When SP_ERR_FAIL is returned, there was an error from the OS,
  52                  * which we can obtain the error code and message for. These
  53                  * calls must be made in the same thread as the call that
  54                  * returned SP_ERR_FAIL, and before any other system functions
  55                  * are called in that thread, or they may not return the
  56                  * correct results. */
  57                 error_code = sp_last_error_code();
  58                 error_message = sp_last_error_message();
  59                 printf("Error: Failed: OS error code: %d, message: '%s'\n",
  60                         error_code, error_message);
  61                 /* The error message should be freed after use. */
  62                 sp_free_error_message(error_message);
  63                 end_program(2);
  64
  65         case SP_ERR_SUPP:
  66                 /* When SP_ERR_SUPP is returned, the function was asked to do
  67                  * something that isn't supported by the current OS or device,
  68                  * or that libserialport doesn't know how to do in the current
  69                  * version. */
  70                 printf("Error: Not supported.\n");
  71                 end_program(3);
  72
  73         case SP_ERR_MEM:
  74                 /* When SP_ERR_MEM is returned, libserialport wasn't able to
  75                  * allocate some memory it needed. Since the library doesn't
  76                  * normally use any large data structures, this probably means
  77                  * the system is critically low on memory and recovery will
  78                  * require very careful handling. The library itself will
  79                  * always try to handle any allocation failure safely.
  80                  *
  81                  * In this example, we'll just try to exit gracefully without
  82                  * calling printf, which might need to allocate further memory. */
  83                 end_program(4);
  84
  85         case SP_OK:
  86         default:
  87                 /* A return value of SP_OK, defined as zero, means that the
  88                  * operation succeeded. */
  89                 printf("Operation succeeded.\n");
  90
  91                 /* Some fuctions can also return a value greater than zero to
  92                  * indicate a numeric result, such as the number of bytes read by
  93                  * sp_blocking_read(). So when writing an error handling wrapper
  94                  * function like this one, it's helpful to return the result so
  95                  * that it can be used. */
  96                 return result;
  97         }
  98 }
  99
 100 int main(int argc, char **argv)
 101 {
 102         /* Call some functions that should not result in errors. */
 103
 104         printf("Getting list of ports.\n");
 105         check(sp_list_ports(&port_list));
 106
 107         printf("Creating a new port configuration.\n");
 108         check(sp_new_config(&config));
 109
 110         /* Now make a function call that will result in an error. */
 111
 112         printf("Trying to find a port that doesn't exist.\n");
 113         check(sp_get_port_by_name("NON-EXISTENT-PORT", &port));
 114
 115         /* We could now clean up and exit normally if an error hadn't occured. */
 116         end_program(0);
 117 }