The structure of memory
Computer memory is a linear sequence
of addressable locations
Addresses are numbered starting at
zero
In personal computers, the smallest
addressable unit is a byte (8 bits)
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Understanding Pointers in C Programming, Slides of Computer Programming
An in-depth explanation of pointers in c programming, including pointer declaration, initialization, assignment, assigning values, seeing the value of a pointer, pointer examples, arrays, assigning addresses to pointers, and pointer arithmetic. It also covers using pointers and modifying behavior in argument passing.
Typology: Slides
2011/2012
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The structure of memory
^ Computer memory is a linear sequenceof addressable locations ^ Addresses are numbered starting atzero ^ In personal computers, the smallestaddressable unit is a byte (8 bits)
MainMemory(RAM)
ControlUnit (CU)Arithmetic-Logic Unit(ALU)CPU
0 - 34 - 7 100 -107108 -109 110 -121^ MemoryAddresses
instr1instr2.^.^. -75^254
... 101.
Memory Organization
program^ data
Pointer
^ Pointer is a variable that keeps anaddress of a variable ^ Need to learn four things aboutpointers^ ^
Declaration Initialization Assignment Pointer’s arithmetic
Declaration
^ Pointers are declared by a name tagand * ^ Examples^ ^
int *xptr;^ ^ xptr is the pointer variable that can point to anyvariable of type int, means it can keep theaddress of an int variable float *avg_ptr;^ ^ avg_ptr is a pointer variable that can keep theaddress of any float type variable
Assignment
^ A bit CONFUSING: assignment also uses*, do not confuse it with the pointerdeclaration int
marks
=^
int
*xptr;
xptr
=^
&marks;
*xptr
=^
/*^ marks
will
be^
equal
to^
Assigning Values to Pointers Set pointer value directly^ ^ double x, *xp = &x;^ ^ *xp = 3.14;^ ^ Make sure pointer has been set to anallocated memory region Setting pointer value to null^ ^ E.g., int *p = 0; int *p = NULL;
Pointer Examples
char *c; (pointer to char, not assigned)int b = 5; int *bptr = &b;char str[8]; char *s = str;
bptr
b s str[0]
str[7] 5
Arrays
^ Accessing array elements^ ^
E.g., int a[8];^ ^ a[0], a[1], … a[7]^
First entry has index 0
^ Array name = pointer to a memoryaddress
Pointer Examples int i = 0;
Pointer Examples 0
NULL
int i = 0;int intPtr = NULL; i*^
intPtr 0x
0x
0x
0x
int i = 0;
Pointer Examples 0
NULL
int i = 0;int intPtr = NULL;intPtr = &i; i*^
intPtr
0x
0x
0x
0x
Pointer Examples 0
0x
0x
0x
i^
intPtr 0x
0x
0x
0x
What do these expressions evaluate to? &i intPtrintPtri &intPtr*
Pointer Examples
0x i^
intPtr
0x
0x
0x
0x
0x
0x
What do these expressions evaluate to? &i^
0x
intPtrintPtri &intPtr*