[SPCA] Start pointers

semester3/spca/code-examples/00_c/00_basics/05_pointers.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main( int argc, char *argv[] ) {
+    int x = 0;
+    int *p = &x;          // Get x's memory address
+    printf( "%p\n", p );  // Print the address of x
+    printf( "%d\n", *p ); // Dereference pointer (get contents of memory location)
+    *p = 10;              // Dereference assign
+    int **dbl_p = &p;     // Double pointer (pointer to pointer to value)
+    int *null_p = NULL;   // Create NULL pointer
+    *null_p = 1;          // Segmentation fault due to null pointer dereference
+
+    // ── pointer arithmetic ───────────────────────────────────────────
+    // Already seen a bit in the c arrays section
+    int arr[ 3 ] = { 2, 3, 4 };
+    char c_arr[ 3 ] = { 'A', 'B', 'C' };
+    int *arr_p = &arr[ 1 ];
+    char *c_arr_p = &c_arr[ 1 ];
+    c_arr_p += 1; // Now points to c_arr[2]
+    arr_p -= 1;   // Now points to arr[0]
+
+    char *arr_p_c = (char *) arr_p; // Cast to char pointer (points to first byte of arr[0])
+    printf( "%d", *( arr_p - 5 ) ); // No boundary checks (can access any memory)
+
+    return EXIT_SUCCESS;
+}

semester3/spca/parts/00_c/01_basics/04_arrays.tex

@@ -1,5 +1,6 @@
 \newpage
 \subsubsection{Arrays}
+\label{sec:c-arrays}
 \lC\ compiler does not do any array bound checks! Thus, always check array bounds.
 Unlike some other programming languages, arrays are \bi{not} dynamic length.
 

semester3/spca/parts/00_c/01_basics/07_pointers.tex

@@ -1 +1,18 @@
+\newpage
 \subsubsection{Pointers}
+On loading of a program, the OS creates the virtual address space for the process, inspects the executable and loads the data to the right places in the address space,
+before other preparations like final linking and relocation are done.
+
+Stack-based languages (supporting recursion) allocate stack in frames that contain local variables, return information and temporary space.
+When a procedure is entered, a stack frame is allocated and executes any necessary setup code (like moving the stack pointer, see later). % TODO: Link to correct section
+When a procedure returns, the stack frame is deallocated and any necessary cleanup code is executed, before execution of the previous frame continues.
+
+\bi{In \lC\ a pointer is a variable whose value is the memory address of another variable}
+
+Of note is that if you simply declare a pointer using \texttt{type * p;} you will get different memory addresses every time.
+The (Linux)-Kernel randomizes the address space to prevent some common exploits.
+\inputcodewithfilename{c}{code-examples/00_c/00_basics/}{05_pointers.c}
+
+\begin{scriptsize}
+    Some pointer arithmetic has already appeared in section \ref{sec:c-arrays}, but same kind of content with better explanation can be found here
+\end{scriptsize}

semester3/spca/spca-summary.tex

@@ -82,4 +82,12 @@
 \section{Hardware}
 \input{parts/02_hw/00_intro.tex}
 
+Remember: Rust and the like have an \texttt{unsafe} block... \lC's equivalent to this is
+\begin{code}{c}
+int main( int argc, char *argv[] ) {
+    // Unsafe code goes here
+}
+\end{code}
+i.e. \bi{YOU are the one that makes \lC\ code safe!}
+
 \end{document}