initalizing arrays

This is a discussion on initalizing arrays within the C++ Programming forums, part of the General Programming Boards category; Hello, Im having a bit of trouble with one of my methods. im new to C++ but have experince in ...

  1. #1
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    Jul 2006
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    4

    initalizing arrays

    Hello,

    Im having a bit of trouble with one of my methods. im new to C++ but have experince in java and this seems ok to me. Basically, all im wanting to do is fill up each array with data calculated elsewhere. When i print out the value of s in the method below its obviously the same as what i put in, but when i print for example volClip[vi], or each of the the elements in the arrays once they are full i get random data. I think its something to do with the way im initializing the arrays but im not exactly sure what. what do i need to do?

    take a look at my code:

    Code:
    void clipBuffer ( float s, char mode )
    {
    	static int 		vi = 0, pi = 0, zi = 0;
    	static float 	       volClip[CLIPSIZE], pitClip[CLIPSIZE], zcrClip[CLIPSIZE];
    	
    	switch (mode) {
    		case 'v':
    			volClip[vi] = s;
    			vi++;
    			printf("Mode %c vi %d\n", mode, vi);
    			printf("data %f",volClip[vi]);
    			break;
    		case 'p':
    			pitClip[pi] = s;
    			pi++;
    			printf("Mode %c pi %d\n", mode, pi);
    			printf("data %f ",pitClip[pi]);
    			break;
    		case 'z':
    			zcrClip[zi] = s;
    			zi++;
    			printf("Mode %c zi %d\n", mode, zi);
    			printf("data %f",zcrClip[zi]);
    			break;
    		
    		default:
    			printf("Incorrect mode selected:\nOptions:\n\t");
    			printf("v - Volume\n\tp - Pitch\n\tz - ZCR\n\te - Energy ratio subband\n");
    			break;
    	}
    	// IF THEY'RE FULL THEN JUST PRINT IT OUT (FOR DEBUGGING)
    	if (vi == CLIPSIZE && pi == CLIPSIZE && zi == CLIPSIZE){
    		vi = 0;
    		pi = 0;
    		zi = 0;
    		int i;
    		printf("VOL\n");
    		for (i = 0; i < CLIPSIZE; ++i) {
    			printf("%d\n",volClip[i]);
    		}
    		printf("PIT\n");
    		for (i = 0; i < CLIPSIZE; ++i) {
    			printf("%d\n",pitClip[i]);
    		}
    		printf("ZCR\n");
    		for (i = 0; i < CLIPSIZE; ++i) {
    			printf("%d\n",zcrClip[i]);
    		}
            }
    }

    Thanks very much for looking!

    Steve

  2. #2
    and the hat of wrongness Salem's Avatar
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    > static float volClip[CLIPSIZE], pitClip[CLIPSIZE], zcrClip[CLIPSIZE];
    Since you said static, these are all initialised to 0.0

    > volClip[vi] = s;
    > vi++;
    > printf("Mode %c vi %d\n", mode, vi);
    > printf("data %f",volClip[vi]);
    You're printing out AFTER you've incremented the count.
    Try
    volClip[vi] = s;
    printf("Mode %c vi %d\n", mode, vi);
    printf("data %f",volClip[vi]);
    vi++;

    It's also a good idea to check whether vi is < CLIPSIZE before doing the assignment.
    Because in order to satisfy this test
    if (vi == CLIPSIZE && pi == CLIPSIZE && zi == CLIPSIZE)
    your code MUST have written off the ends of each of the arrays (not good).
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
    Registered User
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    Jul 2006
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    thanks, yeah they are good tips and how didnt i see that before! its those lazy sundays i guess... also noticed i was doing a %d for a float, hence the bizzare answers. School boy error!

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