Jan 31
followup from Tues
Why Jim likes the separation of typedef and struct :
typedef struct _node *node;
struct _node {
node left;
node right;
};
This is part of a recursive data structure.
Putting the definition of node first means
that it can be used within the struct. (In other
words, each node contains pointers to other nodes.)
chapter 1
Any questions about the overview there?
Discuss these ideas:
- virtual memory
- context shift
- bit, byte, hex, ascii
- cache
homework
First round was generally fine.
The next one is posted. Essentially we'll spend
up to two weeks to get through the end of chapter 2,
spending less time on the floating point at the end.
C : pointers, bits, memory addresses
A lot of what I'm doing here (pointers)
is discussed in chapter 2 of the systems text.
But the C books (e.g. K&R) will also likely
be helpful in mastering this stuff.
- bitwise arithmetic XOR operator ^
- pointer operators * and &
- shows example of command line arguments
/* address.c
*
* Output the memory addresses of some stack and heap variables.
*
* $ gcc address.c -o address
* $ ./address
* address of x is 0xbfc493ec
* address of y is 0xbfc493e8
* value of zptr 0x8f3d008
*/
#include <stdio.h>
#include <stdlib.h>
int main(){
int x;
int y;
int* zptr = (int*) malloc(sizeof(int));
printf(" address of x is %p \n", (void*) &x);
printf(" address of y is %p \n", (void*) &y);
printf(" value of zptr %p \n", (void*) zptr);
return 0;
}
(C errors are often less clear than (say) python.
See the error that happens if you leave out include stdlib.)
On the same machine (cs.marlboro.edu)
$ free -b -t
total used free shared buffers cached
Mem: 3955130368 3478249472 476880896 0 603877376 2536763392
-/+ buffers/cache: 337608704 3617521664
Swap: 3305103360 0 3305103360
Total: 7260233728 3478249472 3781984256
Discuss the relations here between the amount of memory
and the size & form of the pointer descriptions.
Pointers and arrays :
int x[100]; // What is "x" all by itself?
int* x0_ptr = &x[0]; // use some printf statements to look at these.
int* x1_ptr = &x[1];
*(x0_ptr + 3) = 7; // What the heck is this doing?
If we get this far, play around with and discuss this code (from the text)
... and use this to discuss start talking about "big-endian" and "little-endian"
machines. (See pg 40 - 42.)
