Question

Hi I’m working with C and I have a question about assigning pointers.

struct foo
{
   int _bar;
   char * _car[SOME_NUMBER]; // this is meant to be an array of char * so that it can hold pointers to names of cars
}

int foofunc (void * arg)
{
   int bar;
   char * car[SOME_NUMBER];

   struct foo * thing = (struct foo *) arg;

   bar = thing->_bar; // this works fine
   car = thing->_car; // this gives compiler errors of incompatible types in assignment
}

car and _car have same declaration so why am I getting an error about incompatible types? My guess is that it has something to do with them being pointers (because they are pointers to arrays of char *, right?) but I don’t see why that is a problem.

when i declared char * car; instead of char * car[MAXINT]; it compiles fine. but I don’t see how that would be useful to me later when I need to access certain info using index, it would be very annoying to access that info later. in fact, I’m not even sure if I am going about the right way, maybe there is a better way to store a bunch of strings instead of using array of char *?

EDIT: I didn’t mean to use INT_MAX (maximum value of int), it’s just some other int, which is about 20.

Answer 1

You are creating a new array of size MAXINT. I think you want to create a pointer to an array of size MAXINT.

Creating a pointer to an array of char*’s:

The following is an array of size MAXINT to char* elements:

char * car[MAXINT]; 

The following is a pointer to: an array of size MAXINT to char* elements:

char* (*car)[MAXINT];

the following is how you set a pointer to: an array of size MAXINT to char* elements:

char* (*car)[MAXINT];
car = &arg->_car;

---

Other syntax errors in the question:

• You need to have a semicolon after your struct definition.
• You should be using foo* not foo. So it should be:
  struct foo* thing = (struct foo *) arg;
• You should be using thing not arg:
  bar = thing->_bar;
car = thing->_car;