Thread: reference of struct

Hello

How the set testinst[0] char and integer?
What am I doing wrong?

Code:

struct test {
  char c;
  int n
};

void somefunction(struct test *inst) {
  inst[0].c = 'a';
  inst[0].n = 5;
}

int main() {
  struct test testinst[20];
  somefunction(&testinst);
  return 0;
}

Many thanks for help!

If somefunction expects an array as an argument, you should probably pass it an array. Note that testinst is an array, and &testinst is not. (This is why your compiler says "warning: passing arg 1 of 'somefunction' from incompatible pointer type".)

Originally Posted by tabstop

If somefunction expects an array as an argument, you should probably pass it an array. Note that testinst is an array, and &testinst is not. (This is why your compiler says "warning: passing arg 1 of 'somefunction' from incompatible pointer type".)

Code:

void somefunction(struct test *inst[]) {
  inst[0]->c = 'a';
  inst[0]->n = 5;
}

Wont work. What is wrong with the code above?

Thanks.

You're also not passing the function an array of pointers.

You want

Code:

void somefunction(struct test *inst);

so that your function expects an array, and then you want to just pass the array to the function already:

Code:

somefunction(testinst);

Originally Posted by Elysia

It's still

inst[0].c = 'a';
inst[0].n = 5;

This is not a pointer-to-pointer and index operator [] dereferences the pointer.

This wont compile..

I get: error C2231: '.c' : left operand points to 'struct', use '->'

Originally Posted by swoopy

> somefunction(&testinst);
This should be:
somefunction(testinst);

Wouldnt this just pass the value?

Originally Posted by l2u

Wouldnt this just pass the value?

No, because you're passing an array, and arrays are always converted to a pointer to their first element in C/C++.
If you put a & infront of it as you did, you're now passing a pointer to a pointer.

Originally Posted by cpjust

No, because you're passing an array, and arrays are always converted to a pointer to their first element in C/C++.
If you put a & infront of it as you did, you're now passing a pointer to a pointer.

This will still crash the program:

Code:

void somefunction(struct test *inst[]) {
  inst[0].c = 'a';
  inst[0].n = 5;
}

int main() {
  struct test testinst[20];
  somefunction(testinst);
  return 0;
}