bit global_error_flag = 0;
bit global_data_ready_flag = 0;

unsigned char A_Function (void) {
    // Do some stuff

    if ( badness ) {
        global_error_flag = 0;
        global_data_ready_flag = 1;

        return 0;
    }

    if ( data_is_ready_use ) {
        global_data_ready_flag = 1;
    }

    return a_value;
}

void Other_Function (void) {
    unsigned char c;

    c = A_Function();

    if( global_error_flag) {
        // Do error stuff here.
    }
    else
    if( global_data_ready_flag ) {
        // Do data processing here.
    }
    global_error_flag = 0;
    global_data_ready_flag = 0;

}

#define FUNCTION_SETS_FLAGS(code) (code)

FUNCTION_SETS_FLAGS( c = A_Function() );

/*************************************************************************
     * FUNCTION    : <function_name>
     * DESCRIPTION : <function description>
     * PARAMETERS  :
     *  Param1	- <Parameter-1 explanation>
     *  Param2	- <Parameter-2 explanation>
     *  Param3	- <Parameter-3 explanation>
     * RETURN      : <Return value and type>
     * GLOBAL VARIABLES USED:
     *  Global1	- <Global-1 explanation>
     *  Global2	- <Global-2 explanation>
     *  Global3	- <Global-3 explanation>
  *************************************************************************/

unsigned char _a_function(void);

#define A_Function(ret_val) (*(ret_val) = _a_function(), !global_error_flag)

...
unsigned char var;
/* call the function */
if (!A_Function(&var))
{
    /* error! */
}
else
{
    /* use var */
    var++;
}

// Function func
    // Does something
    // Consumes ready_flag and  sets error_flag on error.

    int func()
    {
        if (ready_flag)
        {
            //do something then clear the flag
            if (some_error)
                error_flag = x;
            ready_flag = 0;
        }
        //don't mess with the flags outside of their 'scope'
        return 0;
    }

unsigned char A_Function (bit *p_error_flag, bit *p_data_ready_flag)
{
  ...
}