Pointers in C

I feel like I've lost days of my life I'll never get back...

🤮 I hope I never have to use this page

What are Pointers?

• Variables that store address of another variable
• Only in C/C++ languages

Example

a is stored at location 104

int a;
int *p;

a = 5;
p = &a; (address of a)

print a     // 5
print p     // 104
print &a    // 104
print *p    // 5

*p = 8;
print a     // 8

Arrays

collection of some data types

int a[5];

Access/Modification

O(1)

int main ()
{
    int A[5];
    A[0] = 2;
    A[1] = 4;
    A[2] = 5;
    A[3] = 8;
    A[4] = 1;


    printf ("%d \n", A);         // Base address
    printf ("%d \n", *A);       // value of first element array[0]
    printf ("%d \n", A + 1);    // address of the second element
                                // 1 is actually the offset (size of datatype being used)
                                // if base address is 100 last statement would return 104
                                // 4 being the size an int takes in memory
    printf ("%d \n", *(A + 1)); // prints the value of the second element (4)
                                // if there is no second element it's prints random value
                                // wtf and why am I learning this... I <3 Javascript
}

Address --> Base + Offset

A[3] = *(A + 3)

Pointers and Arrays

Element at i

- Address --> &A[i] or (A + i)
- Value --> A[i] or *(A + i)

A --> pointer to base address
A++ XXX Compilation Error

int *p = A
p++ WORKS

Pointers and Multi Dimensional Arrays

int *p = B          // XXX compilation error
                    // points to 1D array

int (*p)[3] = B;    // works

print B or &B[0]    // starting address of B[0]
print *B or B[0] or &B[0][0]    // starting address of B[0]
print (B+1)         // starting address + size of 1D array of 3 int (12)


print *(B+1) or B[1] or &B[1][0]