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copied!<p>Edit: The reason queue is 2d is because I need a pointer of Command so that cmd can equal NULL. NULL == (void *). This is where I get confused though, and why I've come here. :)</p> <p>To help try and figure out another problem I have in Python, I'm implementing a small test program in C. While I know a little, apparently I'm confused. I'm trying to write a simple queue to be used in asynchronous USB transfers. Something's not right with queue, as every command popped from the queue is the same. If I write queue[1024][0] as queue[1024][1] instead, the command alternates between two distinct commands, and the program crashes in command_thread_main. Apparently it doesn't notice that cmd should be NULL. Changing [1] any higher has no effect as far as I can tell. Any hints?</p> <pre><code>typedef struct Command { void (*cb) (char *data, int size); unsigned char *data; int size; } Command; struct Command queue[1024][0]; int queueEnd = 0; int queueStart = 0; static void queue_push(void (*cb), unsigned char *data, int size) { if (queueEnd >= 1024) return; queue[queueEnd]->cb = cb; queue[queueEnd]->data = data; queue[queueEnd]->size = size; queueEnd++; } struct Command * queue_pop(void) { if( queueStart > queueEnd ) return NULL; return queue[queueStart++]; } static void *command_thread_main(void *arg) { struct Command *cmd; while (!do_exit) { if(locked) continue; locked = 1; cmd = queue_pop(); if(cmd != NULL) cmd->cb(cmd->data, cmd->size); } } </code></pre>

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