passing a pointer member in structure which is member of another structure to a function which accepts double pointer

Question

I have to pass a double pointer to a function

struct Animal{
        uint_32 *count; 
}


struct forest{
      struct Animal elephant;
}

void pass(uint32 **count){
       printf("Count:%d\n",**count);
}

int main(){
   struct  forest *gir;
   gir=(struct forest*)malloc(sizeof(struct forest));
   gir.elephant.count=(int*)malloc(sizeof(uint32_t));

   pass(_______); //have to pass count value
       return 0;
}

I have tried various combos but not sure how to handle this case.

kindly note, I have directly written it on SO, as putting up actual code would be unnecessarily complicating, as I am only looking for specific solution.

[Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). — Sourav Ghosh, Jan 17 '17 at 06:05

score 4 · Accepted Answer · edited May 23 '17 at 12:01

4

Short answer:

pass(&gir->elephant.count);

You need to pass the address of count in elephant in gir.

One of your line can't compile:

// gir.elephant.count=(int *)malloc(sizeof(uint32_t)); this one
gir->elephant.count = malloc(sizeof *gir->elephant.count);
if (gir->elephant.count == NULL) { // you should always check the return of malloc
    free(gir);
    return 1;
}
gir->elephant.count = 42; // maybe you want affect count to something?

Plus you forget ; at the end of your structure declaration. And uint_32, don't exist in stdint.h, you must use uint32_t. @chux notice that you don't use the correct flag to print a uint32_t in printf(), you must use PRIu32.

struct Animal {
    uint32_t *count; 
};

struct forest {
    struct Animal elephant;
};

void pass(uint32_t **count)
   printf("Count:%" PRIu32 "\n", **count);
}

You shoud not cast return of malloc

edited May 23 '17 at 12:01

Community

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answered Jan 17 '17 at 05:49

Stargateur

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thanks, I wrote this directly on so, hence the error – Himanshu Sourav Jan 17 '17 at 06:00
1

I find myself UV-ing `ptr = malloc(sizeof *ptr * n);` answers - it is so simple. Good answer. – chux - Reinstate Monica Jan 17 '17 at 06:52
1

BTW `printf("Count:%d\n",**count);` needs work. Sign-ness and width issues. – chux - Reinstate Monica Jan 17 '17 at 06:54
@HimanshuSourav You should not fix your issues by editing your question that destroy my answer. – Stargateur Jan 17 '17 at 07:19
@Stargateur reverted – Himanshu Sourav Jan 17 '17 at 08:06

passing a pointer member in structure which is member of another structure to a function which accepts double pointer

1 Answers1