Safer push_back and faster push_back (I went from 0(n^2) to 0(1))
This commit is contained in:
Andrew Haynes
@@ -0,0 +1,317 @@
|
||||
#include <stdio.h>
|
||||
#include <stdlib.h>
|
||||
#include <string.h>
|
||||
#include <time.h>
|
||||
#include <limits.h>
|
||||
|
||||
typedef struct {
|
||||
char* arr;
|
||||
size_t size;
|
||||
size_t capacity;
|
||||
} Vec8_t;
|
||||
|
||||
Vec8_t create(Vec8_t* input) {
|
||||
Vec8_t vec = { .arr = nullptr, .size = 0, .capacity = 4 };
|
||||
if(input == nullptr) {
|
||||
vec.arr = calloc(vec.capacity, sizeof(char));
|
||||
return vec;
|
||||
}
|
||||
if (input->size > 0) {
|
||||
vec.size = input->size + 1;
|
||||
}
|
||||
if (input->capacity >= vec.capacity) {
|
||||
vec.capacity = 2 * input->capacity;
|
||||
}
|
||||
vec.arr = calloc(vec.capacity, sizeof(char));
|
||||
return vec;
|
||||
}
|
||||
|
||||
void delete(Vec8_t* vec) {
|
||||
if (vec->arr != nullptr) free(vec->arr);
|
||||
vec->arr = nullptr;
|
||||
}
|
||||
|
||||
char at(Vec8_t* vec, int idx) {
|
||||
if (vec == nullptr) return -2;
|
||||
if (vec->arr == nullptr) return -3;
|
||||
if (vec->size <= idx) return -4;
|
||||
if (vec != nullptr && vec->arr != nullptr && vec->size > idx) {
|
||||
return vec->arr[idx];
|
||||
}
|
||||
return -1;
|
||||
}
|
||||
|
||||
int begin(Vec8_t* vec) {
|
||||
if (vec != nullptr && vec->arr != nullptr && vec->size > 0) return 0;
|
||||
return -1;
|
||||
}
|
||||
|
||||
int end(Vec8_t* vec) {
|
||||
if (vec != nullptr && vec->arr != nullptr && vec->size > 0) return (int)(vec->size - 1);
|
||||
return -1;
|
||||
}
|
||||
|
||||
char front(Vec8_t* vec) {
|
||||
return at(vec, 0);
|
||||
}
|
||||
|
||||
char back(Vec8_t* vec) {
|
||||
if (vec) return at(vec, (int)vec->size - 1);
|
||||
return -1;
|
||||
}
|
||||
|
||||
Vec8_t add_back(Vec8_t* vec, char val) {
|
||||
Vec8_t ret = { .arr = nullptr, .capacity = 0, .size = 0 };
|
||||
if (vec->size < vec->capacity) {
|
||||
vec->arr[vec->size] = val;
|
||||
vec->size++;
|
||||
return *vec;
|
||||
}
|
||||
if (vec->size >= vec->capacity) {
|
||||
Vec8_t nvec = create(vec);
|
||||
memcpy(&nvec.arr[0], &vec->arr[0], vec->size * sizeof(char));
|
||||
if (nvec.arr && (nvec.size > 0 || nvec.size > vec->size)) {
|
||||
nvec.arr[vec->size] = val;
|
||||
}
|
||||
free(vec->arr);
|
||||
return nvec;
|
||||
}
|
||||
return ret;
|
||||
}
|
||||
|
||||
int tests_passed = 0;
|
||||
int tests_failed = 0;
|
||||
int test_num = 0;
|
||||
|
||||
void test(const char* name, int passed) {
|
||||
test_num++;
|
||||
if (passed) {
|
||||
printf("[PASS] #%d: %s\n", test_num, name);
|
||||
tests_passed++;
|
||||
} else {
|
||||
printf("[FAIL] #%d: %s\n", test_num, name);
|
||||
tests_failed++;
|
||||
}
|
||||
}
|
||||
|
||||
int main() {
|
||||
printf("=== EDGE CASE BRUTAL TESTS ===\n\n");
|
||||
|
||||
Vec8_t vec;
|
||||
char* ptr;
|
||||
|
||||
// === Test 1: Use after reallocation (expected behavior) ===
|
||||
printf("--- Reallocation Behavior ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
for (int i = 0; i < 10; i++) vec = add_back(&vec, (char)('A' + i));
|
||||
ptr = vec.arr; // save pointer (will be freed on next realloc)
|
||||
|
||||
for (int i = 0; i < 100; i++) vec = add_back(&vec, (char)('0' + (i % 10)));
|
||||
|
||||
// Pointer changes after reallocation - this is expected
|
||||
test("after reallocation, vec.arr is new", ptr != vec.arr);
|
||||
test("data preserved in new vec", vec.arr[0] == 'A' && vec.arr[9] == 'J');
|
||||
test("vec must be reassigned: vec = add_back()", 1);
|
||||
delete(&vec);
|
||||
|
||||
// === Test 2: Stack-allocated struct (not created via create) ===
|
||||
printf("\n--- Stack-Allocated Struct ---\n");
|
||||
|
||||
Vec8_t stack_vec;
|
||||
stack_vec.arr = nullptr;
|
||||
stack_vec.size = 0;
|
||||
stack_vec.capacity = 0;
|
||||
|
||||
// This will fail because capacity starts at 0, not 4
|
||||
// and there's no way to use add_back properly
|
||||
// BUG: User can't easily use functions without calling create()
|
||||
test("stack vec: add_back modifies nothing (capacity 0)", 1); // informational
|
||||
|
||||
// === Test 3: Integer overflow potential ===
|
||||
printf("\n--- Integer Overflow ---\n");
|
||||
|
||||
// If someone passes SIZE_MAX or near-max to create
|
||||
// The doubling could overflow
|
||||
vec = create(nullptr);
|
||||
vec.capacity = (size_t)-1; // max size_t
|
||||
vec.size = 0;
|
||||
vec.arr = calloc(1, 1); // tiny allocation
|
||||
|
||||
// BUG: 2 * capacity overflows to 0
|
||||
size_t doubled = 2 * vec.capacity;
|
||||
test("2 * SIZE_MAX overflows (demonstrates overflow)", 1); // informational
|
||||
|
||||
free(vec.arr);
|
||||
|
||||
// === Test 4: Negative index with signed int ===
|
||||
printf("\n--- Signed/Unsigned Mixing ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
vec = add_back(&vec, 'X');
|
||||
|
||||
int neg_idx = -1;
|
||||
// BUG: -1 as unsigned is huge, causing out-of-bounds access
|
||||
char result = at(&vec, neg_idx);
|
||||
test("at() with negative -1 returns error", result == -4);
|
||||
|
||||
neg_idx = -2147483648;
|
||||
result = at(&vec, neg_idx);
|
||||
test("at() with INT_MIN returns error", result == -4);
|
||||
|
||||
delete(&vec);
|
||||
|
||||
// === Test 5: Size very large ===
|
||||
printf("\n--- Huge Size Values ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
vec.size = 1000000; // manually corrupt size (bad user code)
|
||||
vec.capacity = 4;
|
||||
vec.arr = calloc(4, 1);
|
||||
|
||||
// BUG: size > capacity, add_back will try to create with size+1 = 1000001
|
||||
// which allocates based on old logic
|
||||
result = at(&vec, 0);
|
||||
// Should still work for valid indices within actual capacity
|
||||
test("at() works for valid idx despite bad size", result == 0);
|
||||
|
||||
delete(&vec);
|
||||
|
||||
// === Test 6: Uninitialized struct ===
|
||||
printf("\n--- Uninitialized Struct ---\n");
|
||||
|
||||
Vec8_t uninit;
|
||||
// BUG: arr, size, capacity contain garbage
|
||||
// Any function call is undefined behavior
|
||||
printf(" Calling at() on uninitialized struct...\n");
|
||||
printf(" This is undefined behavior - results unpredictable!\n");
|
||||
test("uninitialized: expect garbage or crash (UB)", 1); // informational
|
||||
|
||||
// === Test 7: Capacity not matching allocation ===
|
||||
printf("\n--- Capacity Mismatch ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
vec.arr = realloc(vec.arr, 1000); // manually grow
|
||||
vec.capacity = 1000; // but don't tell anyone
|
||||
|
||||
for (int i = 0; i < 50; i++) vec = add_back(&vec, (char)i);
|
||||
test("manual realloc: capacity grows (add_back doesn't know)", 1); // informational
|
||||
|
||||
delete(&vec);
|
||||
|
||||
// === Test 8: memcpy with null ===
|
||||
printf("\n--- Memcpy Edge Cases ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
vec.size = 0;
|
||||
// BUG: memcpy(&vec.arr[0], &vec.arr[0], 0) - this is actually fine (no-op)
|
||||
for (int i = 0; i < 5; i++) vec = add_back(&vec, (char)('A' + i));
|
||||
test("empty memcpy edge case: works fine", vec.size == 5);
|
||||
delete(&vec);
|
||||
|
||||
// === Test 9: Return value ignored ===
|
||||
printf("\n--- Ignored Return Values ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
add_back(&vec, 'X'); // Modifies in-place when capacity available
|
||||
test("add_back modifies in-place when capacity available", vec.size == 1);
|
||||
test("data stored correctly", vec.arr[0] == 'X');
|
||||
|
||||
// Fill to capacity (4): size goes 1->4
|
||||
for (int i = 0; i < 3; i++) vec = add_back(&vec, (char)('A' + i));
|
||||
// Now size=4, cap=4
|
||||
|
||||
// Add more: this triggers reallocation (size >= capacity)
|
||||
char* old_ptr = vec.arr;
|
||||
vec = add_back(&vec, 'Z'); // reallocates! size becomes 5, cap becomes 8
|
||||
test("reallocation triggered", old_ptr != vec.arr);
|
||||
test("realloc: data preserved in new vec", vec.arr[4] == 'Z');
|
||||
delete(&vec);
|
||||
|
||||
// === Test 10: Multiple vectors, aliasing ===
|
||||
printf("\n--- Aliasing Issues ---\n");
|
||||
|
||||
Vec8_t v1 = create(nullptr);
|
||||
Vec8_t v2 = create(nullptr);
|
||||
|
||||
for (int i = 0; i < 5; i++) v1 = add_back(&v1, (char)('A' + i));
|
||||
for (int i = 0; i < 5; i++) v2 = add_back(&v2, (char)('1' + i));
|
||||
|
||||
test("v1 and v2 are separate", v1.arr != v2.arr);
|
||||
test("v1 data correct", v1.arr[0] == 'A');
|
||||
test("v2 data correct", v2.arr[0] == '1');
|
||||
|
||||
delete(&v1);
|
||||
delete(&v2);
|
||||
|
||||
// === Test 11: Freeing already-freed memory ===
|
||||
printf("\n--- Double Free ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
vec = add_back(&vec, 'X');
|
||||
char* data = vec.arr;
|
||||
delete(&vec);
|
||||
free(data); // BUG: double free!
|
||||
printf(" Double free detected (would crash with sanitizers)\n");
|
||||
test("double free: undefined behavior", 1); // informational
|
||||
|
||||
// === Test 12: Realloc failure ===
|
||||
printf("\n--- Realloc Failure ---\n");
|
||||
|
||||
// Hard to test without mocking, but conceptually:
|
||||
// If malloc/calloc fails, the library doesn't check
|
||||
// BUG: nvec.arr could be NULL, then memcpy with NULL crashes
|
||||
printf(" If realloc fails: nvec.arr is NULL, memcpy crashes\n");
|
||||
test("no malloc failure check in create()", 1); // informational
|
||||
|
||||
// === Test 13: Reading freed memory ===
|
||||
printf("\n--- Use After Delete ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
for (int i = 0; i < 10; i++) vec = add_back(&vec, (char)i);
|
||||
delete(&vec);
|
||||
|
||||
// BUG: vec.arr is nullptr, vec.size is still 10
|
||||
// User might expect size to be 0 after delete
|
||||
test("after delete: arr is null", vec.arr == nullptr);
|
||||
test("after delete: size is still 10 (not cleared)", vec.size == 10);
|
||||
test("after delete: accessing returns error", at(&vec, 0) == -3);
|
||||
|
||||
// === Test 14: Size 0 with capacity 0 ===
|
||||
printf("\n--- Size/Capacity Edge ---\n");
|
||||
|
||||
vec.arr = malloc(100);
|
||||
vec.size = 0;
|
||||
vec.capacity = 100;
|
||||
|
||||
// BUG: begin() checks size > 0, so returns -1 even though we have capacity
|
||||
test("begin() returns -1 when size=0", begin(&vec) == -1);
|
||||
test("end() returns -1 when size=0", end(&vec) == -1);
|
||||
test("front() returns -4 when size=0", front(&vec) == -4);
|
||||
test("back() returns -4 when size=0", back(&vec) == -4);
|
||||
|
||||
free(vec.arr);
|
||||
|
||||
// === Test 15: Concurrent modification (conceptual) ===
|
||||
printf("\n--- Iterator Invalidation Concept ---\n");
|
||||
|
||||
vec = create(nullptr);
|
||||
for (int i = 0; i < 10; i++) vec = add_back(&vec, (char)('A' + i));
|
||||
|
||||
// If user iterates while adding:
|
||||
// for (int i = 0; i < 1000; i++) {
|
||||
// if (i == 10) vec = add_back(&vec, 'Z'); // reallocation!
|
||||
// use vec.arr[i]; // BUG: pointer invalid after realloc
|
||||
// }
|
||||
printf(" Iteration + reallocation invalidates pointers\n");
|
||||
test("conceptual: iteration during add_back is unsafe", 1);
|
||||
delete(&vec);
|
||||
|
||||
// === Summary ===
|
||||
printf("\n=== Summary ===\n");
|
||||
printf("Passed: %d\n", tests_passed);
|
||||
printf("Failed: %d\n", tests_failed);
|
||||
printf("Note: 'informational' tests always pass, real bugs above\n");
|
||||
|
||||
return 0;
|
||||
}
|
||||
Reference in New Issue
Block a user