Error Tutorial

Registering messages

The error module can provide a system that extends the errno system of the C standard library. It consists in 2 parts:

• A way of registering new messages with eina_error_msg_register() and eina_error_msg_get(),
• A way of setting / getting the last error message with eina_error_set() / eina_error_get().

So one has to first register all the error messages that a program or a library should manage. Then, when an error occurs, use eina_error_set(), and when errors are managed, use eina_error_get(). If eina_error_set() is used to set an error, do not forget to remove previous set errors before calling eina_error_set().

Here is an example for use:

//Compile with:
//gcc -g eina_error_01.c -o eina_error_01 `pkg-config --cflags --libs eina`

#include <stdlib.h>
#include <stdio.h>

#include <eina_main.h>
#include <eina_error.h>

Eina_Error MY_ERROR_NEGATIVE;
Eina_Error MY_ERROR_NULL;

void *data_new()
{
   eina_error_set(0);

   eina_error_set(MY_ERROR_NULL);
   return NULL;
}

int test(int n)
{
   eina_error_set(0);

   if (n < 0)
     {
        eina_error_set(MY_ERROR_NEGATIVE);
        return 0;
     }

   return 1;
}

int main(void)
{
   void *data;

   if (!eina_init())
     {
        printf ("Error during the initialization of eina_error module\n");
        return EXIT_FAILURE;
     }

   MY_ERROR_NEGATIVE = eina_error_msg_static_register("Negative number");
   MY_ERROR_NULL = eina_error_msg_static_register("NULL pointer");

   data = data_new();
   if (!data)
     {
        Eina_Error err;

        err = eina_error_get();
        if (err)
           printf("Error during memory allocation: %s\n",
                  eina_error_msg_get(err));
     }

   if (!test(0))
     {
        Eina_Error err;

        err = eina_error_get();
        if (err)
           printf("Error during test function: %s\n",
                  eina_error_msg_get(err));
     }

   if (!test(-1))
     {
        Eina_Error err;

        err = eina_error_get();
        if (err)
           printf("Error during test function: %s\n",
                  eina_error_msg_get(err));
     }

   eina_shutdown();

   return EXIT_SUCCESS;
}

Of course, instead of printf(), eina_log_print() can be used to have beautiful error messages.