Pointers In C
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C++ Pointers and C Strings
CS1 - Pointers
1
Pointers A pointer is a variable that holds the address of something else. int foo; foo int *x;
0 1 2 3 4 5
123
x
81345 81346 81347
CS1 - Pointers
...
...
foo = 123; x = &foo;
Address
MEMORY
3 2
int *x; • x is a pointer to an integer. • You can use the integer x-points-to in a C++ expression like this: “the int x points to” y = *x + 17;
*x = *x +1; CS1 - Pointers
3
&foo In C++ you can get the address of a variable with the “&” operator. int foo; foo = 123; x = &foo;
Address
0 1 2 foo 3 4 5
...
CS1 - Pointers
123 ...
&foo means “the address of foo”
MEMORY
4
Assigning a value to a dereferenced pointer A pointer must have a value before you can dereference it (follow the pointer). int *x; *x=3; !! ! R o O ERR n’t point t s x doe
!! ! g n i anyth
int foo; int *x; x = &foo; *x=3; ne i f s i oo f this o t ts n i o p x
CS1 - Pointers
5
Pointers to anything x
int *x; int **y;
double *z;
y
some *int
z
CS1 - Pointers
some int
some int
some double
6
Pointers and Arrays • An array name is basically a const pointer. • You can use the [] operator with a pointer: x is “the address of a[2] ” int *x; int a[10]; x = &a[2]; for (int i=0;i<3;i++) x[i]++; x[i] is the same as a[i+2] CS1 - Pointers
7
Pointer arithmetic • Integer math operations can be used with pointers. • If you increment a pointer, it will be increased by the size of whatever it points to. int *ptr = a;
*(ptr+2)
*ptr a[0]
a[1]
a[2]
a[3]
*(ptr+4)
a[4]
int a[5]; CS1 - Pointers
8
printing an array void print_array(int a[], int len) { for (int i=0;i
CS1 - Pointers
1
Pointers A pointer is a variable that holds the address of something else. int foo; foo int *x;
0 1 2 3 4 5
123
x
81345 81346 81347
CS1 - Pointers
...
...
foo = 123; x = &foo;
Address
MEMORY
3 2
int *x; • x is a pointer to an integer. • You can use the integer x-points-to in a C++ expression like this: “the int x points to” y = *x + 17;
*x = *x +1; CS1 - Pointers
3
&foo In C++ you can get the address of a variable with the “&” operator. int foo; foo = 123; x = &foo;
Address
0 1 2 foo 3 4 5
...
CS1 - Pointers
123 ...
&foo means “the address of foo”
MEMORY
4
Assigning a value to a dereferenced pointer A pointer must have a value before you can dereference it (follow the pointer). int *x; *x=3; !! ! R o O ERR n’t point t s x doe
!! ! g n i anyth
int foo; int *x; x = &foo; *x=3; ne i f s i oo f this o t ts n i o p x
CS1 - Pointers
5
Pointers to anything x
int *x; int **y;
double *z;
y
some *int
z
CS1 - Pointers
some int
some int
some double
6
Pointers and Arrays • An array name is basically a const pointer. • You can use the [] operator with a pointer: x is “the address of a[2] ” int *x; int a[10]; x = &a[2]; for (int i=0;i<3;i++) x[i]++; x[i] is the same as a[i+2] CS1 - Pointers
7
Pointer arithmetic • Integer math operations can be used with pointers. • If you increment a pointer, it will be increased by the size of whatever it points to. int *ptr = a;
*(ptr+2)
*ptr a[0]
a[1]
a[2]
a[3]
*(ptr+4)
a[4]
int a[5]; CS1 - Pointers
8
printing an array void print_array(int a[], int len) { for (int i=0;i
Pointers In C
November 2019 17
Pointers In C++
June 2020 6
C Programming Using Pointers
April 2020 7
11. C Programming - Pointers
May 2020 9
Pointers
November 2019 36