Loops to control a function element

**RCON** · 10-17-2006

I really don't know the best way to search for an answer so I am going to try to explain my problem.

I am writing a drum machine program and I have some parts in the code that I think could be made smaller. The biggest problem I have is that I don't know how to dynamically change an element in a function call.

For example I would like to change this:

Code:

hitFunc(void) {
            wavPlay(sample0, vol, bal, etc);
            wavPlay(sample1 vol, bal, etc);
            wavPlay(sample2 vol, bal, etc);
            wavPlay(sample3 vol, bal, etc);
            wavPlay(sample4 vol, bal, etc);
            wavPlay(sample5 vol, bal, etc);
            wavPlay(sample6 vol, bal, etc);
            //etc…
}

To something like this:

Code:

hitFunc(void) {
            for(X=0; X < 16; X++) {
                        wavPlay(sampleX vol, bal, etc);
            }
}

The issue I have is that sample0 is a structure of memory and I don’t know how to point it to sampleX where X is a variable number in a loop and have it work.

Any help would be appreciated!!!

**yxunomei** · 10-17-2006

> The issue I have is that sample0 is a structure of memory and I don’t know how to point it to sampleX where X is a variable number in a loop and have it work.

structure of memory? do you mean struct?

you can make it an array if you want

Code:

 hitFunc() {
   for(x = 0; x < 16; x++) {
      wavPlay(sample[x].vol, bal, etc);
   }
}

**dwks** · 10-17-2006

If the OP hasn't thought of that, [s]he probably hasn't learned about arrays yet: CProgramming.com Tutorial: Lesson 8: Arrays.

**RCON** · 10-17-2006

Yes, it is a struct with a variable size of data that hold the data for the wave audio. I thought about using an array but can you do that and make it dynamic? You can load/unload wave audio on the fly and the size can be as big as there is free ram. With an array wouldn't I have to set the data size to a fixed value?

**dwks** · 10-17-2006

Yes, you would. You should use dynamically allocated arrays if you don't know the size in advance. Look up realloc().

[edit] Here's a sample I wrote using realloc(). It's not very well written, but it might give you some idea of what to do: http://cboard.cprogramming.com/showp...14&postcount=5 [/edit]

**RCON** · 10-17-2006

Ok, I'll look up realloc, but I have one more question.

If I create an array of my struct.
In array element 1 I have a 1mb sample.
In array element 2 I have a 3mb sample.
In array element 3 I have a 0.5mb sample.

Then I free the memory for element 1 and realloc 2mb to load a new sample. Would the pointers for element 2 and 3 move dynamically or would I need to realloc the whole array?

Thanks for the help by the way!

**dwks** · 10-17-2006

malloc() allocates memory. realloc() resizes memory. (If no memory has been allocated, realloc() is like malloc().)

Therefore, to create an array, you would realloc() an array slightly bigger for each element you wanted to add. The elements of the array could be pointers to 1mb of memory or whatever; these would be separate. You would malloc() these and free() them when you remove an element from the array.

Hope that helps. You could try a man page: http://www.uwm.edu/cgi-bin/IMT/wwwma...3%29&msection=

[edit] This might compile, I haven't tried it:

Code:

#include <stdio.h>
#include <stddef.h>  /* for size_t */
#include <stdlib.h>  /* for malloc(), realloc(), and strtol() */
#include <ctype.h>  /* for isspace() */

struct person_t {
    char *name;
    size_t len;
    long age;
};

int main(void) {
    struct person_t *array = 0, *temparray;
    size_t elements = 0, x;
    char buffer[BUFSIZ], *p;
    long age;

    while(fgets(buffer, sizeof(buffer), stdin)) {
        age = strtol(buffer, &p, 0);
        while(isspace(*p)) p ++;

        temparray = realloc(array, sizeof(struct person_t) * (elements + 1));
        if(!temparray) break;  /* out of memory */
        array = temparray;

        array[elements].len = strlen(p);

        array[elements].name = malloc(array[elements].len+1);  /* +1 for NULL */
        if(!array[elements].name) break;
        strcpy(array[elements].name, p);

        array[elements].age = age;

        elements ++;
    }

    for(x = 0; x < elements; x ++) {
        printf("%s [%zu chars], age %ld\n", array[x].name, array[x].len, array[x].age);
        free(array[x].name);
    }

    free(array);

    return 0;
}

[/edit]

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