[SPCA] Restructuring, finish memory management in C, start dynamic memory management section

semester3/spca/code-examples/00_c/00_basics/02_declarations.c

@@ -14,6 +14,13 @@ struct MyStruct {
         int el2;
 };
 
+// Like structs, but can only hold one of the values!
+union MyUnion {
+        int ival;
+        float fval;
+        char *sval;
+};
+
 int fun( int j ) {
     static int i = 0;              // Persists across calls of fun
     short my_var = 1;              // Block scoped (deallocated when going out of scope)
@@ -27,7 +34,10 @@ int main( int argc, char *argv[] ) {
     }
     struct MyStruct test;            // Allocate memory on stack for struct
     struct MyStruct *test_p = &test; // Pointer to memory where test resides
-    test.el1 = 1;                    // Direct element access
-    test_p->el2 = 2;                 // Via pointer
+    struct MyStruct test2;
+    union MyUnion my_uval; // Work exactly like structs for access
+    test.el1 = 1;          // Direct element access
+    test_p->el2 = 2;       // Via pointer
+    test2 = test;          // Copies the struct
     return 0;
 }

semester3/spca/code-examples/00_c/02_memory/00_memory.c

@@ -0,0 +1,22 @@
+#include <stdlib.h>
+
+int main( int argc, char *argv[] ) {
+    long *arr = (long *) malloc( 10 * sizeof( long ) ); // Allocate on heap
+    if ( arr == NULL )                                  // Check if successful
+        return EXIT_FAILURE;
+    arr[ 0 ] = 5;
+
+    long *arr2;
+    if ( ( arr2 = (long *) calloc( 10, sizeof( long ) ) ) == NULL )
+        return EXIT_FAILURE; // Same as above, but fewer lines and memory zeroed
+
+    // Reallocate memory (to change size). Always use new pointer and do check!
+    if ( ( arr2 = (long *) realloc( arr2, 15 * sizeof( long ) ) ) == NULL )
+        return EXIT_FAILURE;
+
+    free( arr );  // Deallocate the memory
+    arr = NULL;   // Best practice: NULL pointer
+    free( arr2 ); // *Can* omit NULLing pointer because end
+
+    return EXIT_SUCCESS;
+}

semester3/spca/code-examples/00_c/02_memory/01_mem-corruption.c

@@ -0,0 +1,15 @@
+#include <stdlib.h>
+
+int main( int argc, char **argv ) {
+    int a[ 2 ];
+    int *b = malloc( 2 * sizeof( int ) ), *c;
+    a[ 2 ] = 5;          // assign past the end of an array
+    b[ 0 ] += 2;         // assume malloc zeroes out memory
+    c = b + 3;           // mess up your pointer arithmetic
+    free( &( a[ 0 ] ) ); // pass pointer to free() that wasn't malloc'ed
+    free( b );
+    free( b );  // double-free the same block
+    b[ 0 ] = 5; // use a free()'d pointer
+    // any many more!
+    return 0;
+}