Thread: malloc ... WHY ?

hi all ,

i hope you can help me with the following :
in types.h :

Code:

/* Structure of input buffer for each switch */
typedef struct InputBuffer *InputBufferPtr;
typedef struct {
	struct List **fifo; 	/* Input fifos: one per output. */
  
	void *traffic; 			/* Placeholder for traffic stats for this input */
	int (*trafficModel)();  /* Traffic generating function */
	Stat bufferStats;		/* Aggregate occupancy statistics for this input. */
	struct Histogram bufferHistogram;	/* Agg occupancy statistics for this input. */
	int  numOverflows;		/* Total number of cells dropped at this input. */
  
	struct List **mcastFifo;		/* Multicast queue for this input. */
  
	// #ifdef use_gbvoq
	struct List *inputPriorityList ;	/* IPL queue for this input. */
	// #endif

} InputBuffer;

in create.c :

Code:

#ifdef use_gbvoq
		inputBuffer->inputPriorityList = (struct List *)malloc( sizeof(struct List)) ;
		if( inputBuffer->inputPriorityList == NULL )	FatalError("createInputBuffer(): Malloc failed.\n") ;
		inputBuffer->inputPriorityList = createList(inputBufferName) ;
		assert( inputBuffer->inputPriorityList != NULL ) ;
	#endif

but, when i am going to make use of the linked list inputPriorityList in defaultInputAction.c :

Code:

/* GBVOQ : All cells belong to a VOQ and to an (per input port) IPL. */
			if( use_gbvoq )
			{
				// assert( aSwitch->inputBuffer[input] != NULL ) ;
				assert( aSwitch->inputBuffer[input]->inputPriorityList != NULL ) ;
				/* Add cell to IPL. */
				if( aSwitch->inputBuffer[input]->fifo[pri]->number == 1 ) /* Cell has already been added to a VOQ. = empty VOQ. */
					addElementAtHead(aSwitch->inputBuffer[input]->inputPriorityList, anElement) ;

the assert fails and if i remove it, i get a bus error in
addElementAtHead fuction

Basically, the aSwitch->inputBuffer[input]->inputPriorityList is NULL and i do NOT know WHY ...

i would be thankful if you help me overcome this problem
thanx

Technically, this is a guess, but I feel good about it: You probably know that the value of x cannot be changed by the following function:

Code:

int no_changing_x(int x) {}

because things are passed by value. That's always true, regardless of the type of x:

Code:

int no_changing_inputBuffer(InputBufferPtr inputBuffer)

What inputBuffer points to can be changed, but if you do, say,

Code:

inputBuffer = malloc(*inputBuffer);

inside that function, that's just too bad, because that memory has been leaked when you exit the function (the value of the pointer in the calling function can't change).

You have one malloc and you check if it fails or not. Provide more code.
Ooo. Guessing time: I put all my money on what tabstop said