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@willcrichton willcrichton/badvector.c Secret
Last active Feb 5, 2018

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#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
// There are at least 7 bugs relating to memory on this page.
// Find them all!
// Vec is short for "vector", a common term for a resizable array.
// For simplicity, our vector type can only hold ints.
typedef struct {
int* data; // Pointer to our array on the heap
int length; // How many elements are in our array
int capacity; // How many elements our array can hold
} Vec;
Vec* vec_new() {
Vec vec; = NULL;
vec.length = 0;
vec.capacity = 0;
return &vec;
void vec_push(Vec* vec, int n) {
if (vec->length == vec->capacity) {
int new_capacity = vec->capacity * 2;
int* new_data = (int*) malloc(new_capacity);
for (int i = 0; i < vec->length; ++i) {
new_data[i] = vec->data[i];
vec->data = new_data;
vec->capacity = new_capacity;
vec->data[vec->length] = n;
void vec_free(Vec* vec) {
void main() {
Vec* vec = vec_new();
vec_push(vec, 107);
int* n = &vec->data[0];
vec_push(vec, 110);
printf("%d\n", *n);
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