[syslog-ng] need help understanding logqueue-fifo.c code

[Szalay Attila]

Hi All!

2012. 03. 7, szerda keltezéssel 21.24-kor Evan Rempel ezt írta:
> I am having difficulties understanding the code that handles the LogQueueFifo objects.
> 
> For instance
> 
> static void log_queue_fifo_push_head(LogQueue *s, LogMessage *msg, const LogPathOptions *path_options)
> {
>     LogQueueFifo *self = (LogQueueFifo *) s;
>     LogMessageQueueNode *node;
> 

The LogQueueFifo structure is defined like this:
typedef struct _LogQueueFifo
{
  LogQueue super;

  /* scalable qoverflow implementation */
  struct list_head qoverflow_output;
[...]

You could spot that the first member of the LogQueueFifo is LogQueue
type and also important that not a pointer but an embedded field.

With this and knowing the method how the C create this type of embedding
structures you could cast a LogQueueFifo type to LogQueue.

This is some type of poor's man inheritance in C.


-- 
Attila Szalay
Product Security Specialist

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