/*
 * Copyright (c) 2020, Dive into Systems, LLC
 * https://diveintosystems.org/
 *
 * Example program with Heap memory access errors
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* a mystery function that takes a string and returns an int value */
int foo(char *str) {
    char a[5];	// Valgrind can't find mem access errors with
    char b[5];  // variables statically allocated on the Stack
    char *c;	// But it can with dynamically allocated Heap memory
    int i;

    c = (char *)malloc(sizeof(char)*5);  // bad code - doesn't check for error

    strcpy(a, "aaaa");
    strcpy(b, "bbbb");
    strcpy(c, "cccc");

    for (i=0; i <=5; i++) {
        a[i] = str[i];      // here we are going beyond the bounds
                            // of "a", but valgrind can't detect it
    }                       // because the array is on the Stack
    for (i=0; i <=5; i++) {
        c[i] = str[i];      // here we are going beyond the bounds
    }                       // of the array, and valgrind can detect
                            // it because the array is in the Heap

    printf("a = %s, b = %s, c = %s\n", a, b, c);

    // here we are forgetting to free malloced space for c before
    // exiting this function: this is a memory leak
    return 0;
}
/****************************************************/
/* main function with some bad memory access errors */
int main(int argc, char *argv[]) {

    char *s;

    s = (char *)malloc(sizeof(char)*8);
    strcpy(s, "ssssss");

    foo(s);  // calling foo with an allocated and initialized string
    printf("s = %s\n", s);
    free(s);  // deallocate space for s

    s = (char *)malloc(sizeof(char)*8);
    foo(s);   // calling foo with an allocated but uninitialized string

    free(s);  // deallocate space for s
    foo(s);   // calling foo with an unallocated and uninitialized string

    s = (char *)malloc(sizeof(char)*8);
    strcpy(s, "xxxx");
    printf("s = %s\n", s);
    s = (char *)malloc(sizeof(char)*8); // a memory leak 
    printf("s = %s\n", s);  // uninitialized read
    free(s);
    free(s);  // freeing already free'ed memory

    return 0;
}