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181 lines
4.0 KiB
181 lines
4.0 KiB
#include <stdlib.h>
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#include <stdio.h>
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// macro for easier using of saferfree function
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#define safeFree(p) saferFree((void**) &(p))
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// typedefs
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typedef int (*t_fptr)(int);
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typedef int (*t_fptr_op)(int, int);
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typedef void (*t_fptr_base)();
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// function declarations
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void allocateArray(int **arr, size_t size, int value);
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void allocateArrayWrong(int *arr, int size, int value);
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void saferFree(void **pointer);
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int square(int num);
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int add(int a, int b);
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int sub(int a, int b);
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//int err(int a, int b);
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void err(void);
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int operation(t_fptr_op op, int a, int b);
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t_fptr_op select(char opc);
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void initialiseOperationsArray(void);
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int evalArray(char opc, int a, int b);
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t_fptr_op operations[128] = {NULL};
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// pointer by reference
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void allocateArray(int **arr, size_t size, int value) {
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int *array = (int*) malloc(size * sizeof(int));
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if (array != NULL) {
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for (size_t index = 0; index < size; index++) {
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array[index] = value;
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}
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}
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*arr = array;
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}
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// pointer by value -> this will not work
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void allocateArrayWrong(int *arr, int size, int value) {
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arr = (int*) malloc(size * sizeof(int));
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if(arr != NULL) {
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for(int i = 0; i < size; i++) {
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arr[i] = value;
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}
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}
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}
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// safer free version which checks for NULL pointer
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// assigns NULL after freeing the pointer
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void saferFree(void **pointer) {
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if (pointer != NULL && *pointer != NULL) {
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free(*pointer);
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*pointer = NULL;
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}
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}
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// simple (unsafe) addition function
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int add(int a, int b) {
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return a + b;
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}
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// simple (unsafe) subtract function
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int sub(int a, int b) {
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return a - b;
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}
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int operation(t_fptr_op op, int a, int b) {
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return op(a, b);
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}
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// simple (unsafe) square function
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int square(int num) {
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return num * num;
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}
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// function selector
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// returns pointer to selected function
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t_fptr_op select(char opc) {
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switch (opc) {
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case '+': return add;
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case '-': return sub;
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default : return (t_fptr_op) err;
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}
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}
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// error function
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void err(void) { //int a, int b) {
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fprintf(stderr, "invalid operation!\n");
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//return 42;
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}
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// evaluate given operation on a & b
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// operation is given by function pointer
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int eval(char opc, int a, int b) {
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t_fptr_op operation = select(opc);
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return operation(a, b);
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}
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// initialise operations array
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// with pointers to add & sub functions
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void initialiseOperationsArray(void) {
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operations['+'] = add;
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operations['-'] = sub;
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}
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// eval function which works with
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// the array of function pointers
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int evalArray(char opc, int a, int b) {
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t_fptr_op operation;
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operation = operations[opc];
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return operation(a, b);
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}
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int main (void) {
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// variable definitions
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size_t size = 8;
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int value = 5;
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int *vector = NULL;
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//int (*fptr0) (int);
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t_fptr fptr0;
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// print vector address
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printf("before malloc: %p\n", vector);
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// function calls
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allocateArray(&vector, size, value);
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//allocateArrayWrong(vector_wrong, size, value);
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for (size_t index = 0; index < size; index++) {
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printf("%u : %d\n", (unsigned int) index, vector[index]);
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}
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// print vector address
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printf("before safeFree: %p\n", vector);
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//saferFree((void**)&(vector));
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safeFree(vector);
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// print vector address after free
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printf("after safeFree: %p\n", vector);
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// function pointer fptr0 now points to square()
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fptr0 = square;
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// call function which fptr0 points to
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printf("%d squared is %d\n", value, fptr0(value));
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// test of function pointers as function parameters
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printf("%u + %d = %d\n", (unsigned int) size, value, operation(add, size, value));
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printf("%u - %d = %d\n", (unsigned int) size, value, operation(sub, size, value));
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// test of fucntion pointer returning
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printf("%d\n", eval('t', size, value));
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// function pointer casting
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t_fptr_base basePointer;
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t_fptr_op fptrFirst = add;
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basePointer = (t_fptr_base) fptrFirst;
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fptrFirst = (t_fptr_op) basePointer;
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printf("%d\n", fptrFirst(5,6));
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// return value
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return 0;
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}
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