我是C的新手，我一直在写一个简单的脚本，如下所示：
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef enum {FALSE, TRUE} bool;
// item_t: information for a single item to be purchased
typedef struct _item_t {
char name[50];
int price;
int quantity;
} item_t;
// cart_t: information for the shopping cart
typedef struct _cart_t {
item_t *items[10];
int size;
} cart_t;
// Returns index of item with name `item_name` in the `items` array inside of `cart`. Returns -1 if not found.
int find_item(cart_t *cart, const char* item_name) {
int i;
for(i=0;i<sizeof(*cart);++i){
if(strcmp(cart->items[i]->name,item_name) == 0){
return i;
}
}
if(i == sizeof(*cart) -1)
return -1;
return 0;
}
// Adds item to cart's items array, if the cart is not full. Returns `FALSE` if the cart is full, and returns `TRUE` otherwise.
bool add_new_item(cart_t *cart, item_t *item) {
if(10 == cart->size)
return FALSE;
else{
int i = cart->size;
cart->items[i] = item;
cart->size +=1;
return TRUE;
}
}
// Increases quantity by one of item with name `item_name` inside of `cart`, if such an item exists.
void add_existing_item(cart_t *cart, const char* item_name) {
int i = find_item(cart,item_name);
if(i == -1)
return;
else{
cart->items[i]->quantity += 1;
}
}
// Removes item with name from cart's items array. Returns a pointer to the removed item, and shifts the items to the right of the deleted item in the `items` array
// left to fill in the gap.
// If the item is not found, return NULL.
item_t* remove_item(cart_t *cart, char *remove_me) {
item_t *p;
int j = 0;
int i = find_item(cart,remove_me);
if(i == -1)
return NULL;
else{
if(i == cart->size-1){
p = cart->items[i];
cart->items[i] = NULL;
}else{
p = cart->items[i];
for(j=i;j<cart->size-1;++j){
cart->items[j] = cart->items[j+1];
}
cart->items[cart->size-1] = NULL;
cart->size -= 1;
}
return p;
}
}
// Determines and returns the total cost of items in cart.
int total_cost(cart_t *cart) {
int total;
int i;
for(i=0;i<sizeof(*cart);++i){
total += cart->items[i]->quantity * cart->items[i]->price;
}
return total;
}
//print item's info and cost.
void print_item_cost(item_t *item) {
printf("%s %d @ $%d = $%d\n", item->name, item->quantity,
item->price, (item->price * item->quantity));
}
//print the shopping cart info
void print_total(cart_t *cart) {
int i = 0;
int cost = 0;
printf("Number of Items: %d\n\n", num_items(cart));
if (cart->size > 0) {
for (i = 0; i < cart->size; ++i) {
print_item_cost(cart->items[i]);
}
}
else {
printf("SHOPPING CART IS EMPTY\n");
}
cost = total_cost(cart);
printf("\nTotal: $%d\n", cost);
}
//this function clears items in the cart
void clear_cart(cart_t *cart) {
int i = 0;
for (i = 0; i < cart->size; i++) {
free(cart->items[i]);
}
cart->size = 0;
}
//a menu of options to manipulate the shopping cart
void print_menu(cart_t *cart) {
char choice = ' ';
char name[50] = "";
int price = 0;
int quantity = 0;
int i = 0;
char c = ' ';
item_t *item;
while(choice != 'q') {
printf("MENU\n");
printf("a - Add item to cart\n");
printf("r - Remove item from cart\n");
printf("c - Change item quantity\n");
printf("o - Output shopping cart\n");
printf("q - Quit\n\n");
while (choice != 'a' &&
choice != 'r' &&
choice != 'c' &&
choice != 'o' &&
choice != 'q') {
printf("Choose an option: ");
scanf(" %c", &choice);
printf("\n");
}
switch (choice) {
case 'a':
while ((c = getchar()) != EOF && c != '\n');
printf("ADD ITEM TO CART\n");
printf("Enter the item name: ");
fgets(name, 50, stdin);
printf("\n");
i = find_item(cart, name);
if (i != -1) {
printf("Item found. Updating quantity of item. \n");
add_existing_item(cart, name);
choice = ' ';
printf("\n");
break;
}
if (cart->size >= 10) {
printf("Cart full. Cannot add new item. \n");
choice = ' ';
printf("\n");
break;
}
printf("Enter the item price: ");
scanf("%d", &price);
printf("\n");
printf("Enter the item quantity: ");
scanf("%d", &quantity);
printf("\n");
item = (item_t*)malloc(sizeof(item_t));
strcpy(item->name, name);
item->price = price;
item->quantity = quantity;
add_new_item(cart, item);
choice = ' ';
printf("\n");
break;
case 'r':
while ((c = getchar()) != EOF && c != '\n');
printf("REMOVE ITEM FROM CART\n");
printf("Enter name of item to remove: ");
fgets(name, 50, stdin);
printf("\n");
item = remove_item(cart, name);
if (item == NULL) {
printf("Item not found. \n");
}
else {
printf("Item removed. \n");
free(item);
}
choice = '\0';
printf("\n");
break;
case 'c':
while ((c = getchar()) != EOF && c != '\n');
printf("CHANGE ITEM QUANTITY\n");
printf("Enter the item name: ");
fgets(name, 50, stdin);
printf("\n");
i = find_item(cart, name);
if (i == -1) {
printf("Item not found. \n");
choice = ' ';
printf("\n");
break;
}
printf("Enter the item price: ");
scanf("%d", &price);
printf("\n");
printf("Enter the new quantity: ");
scanf("%d", &quantity);
printf("\n");
update_item_in_cart(cart, name, price, quantity);
choice = '\0';
printf("\n");
break;
case 'o':
while ((c = getchar()) != EOF && c != '\n');
printf("OUTPUT SHOPPING CART\n");
print_total(cart);
choice = ' ';
printf("\n");
break;
}
}
clear_cart(cart);
}
int main(){
// malloc
cart_t *cart;
cart = (cart_t*)malloc(sizeof(cart_t));
cart->size = 0;
print_menu(cart);
//free
free(cart);
return 0;
}
它可能看起来很长，但想法很简单，它模拟购物车中的项目，它接受命令添加项目/删除项目/更改数量/显示当前购物车信息。但是，在调试的最开始，当我在命令窗口中执行以下操作时：
$ ./try
MENU
a - Add item to cart
r - Remove item from cart
c - Change item quantity
o - Output shopping cart
q - Quit
Choose an option: a
ADD ITEM TO CART
Enter the item name: tira
Segmentation fault (core dumped)
我遇到了分段错误。我想知道这里的错误是什么？我是C的新手，并且不确定我的代码中指针内容的正确性。
PS： 感谢您的回复，是的，这有助于我解决add_new_item函数中的错误。但是，当我调试remove_item时，它会再次终止并出现分段错误，命令行如下所示：
$ ./try
MENU
a - Add item to cart
r - Remove item from cart
c - Change item quantity
o - Output shopping cart
q - Quit
Choose an option: a
ADD ITEM TO CART
Enter the item name: shoes
Enter the item price: 1
Enter the item quantity: 2
MENU
a - Add item to cart
r - Remove item from cart
c - Change item quantity
o - Output shopping cart
q - Quit
Choose an option: r
REMOVE ITEM FROM CART
Enter name of item to remove: shoes
Item removed.
MENU
a - Add item to cart
r - Remove item from cart
c - Change item quantity
o - Output shopping cart
q - Quit
Choose an option: o
OUTPUT SHOPPING CART
Segmentation fault (core dumped)
答案 0 :(得分：3)
至少有一个问题是find_item功能。 sizeof(*cart)与购物车中的实际项目数无关，sizeof返回数据结构中的字节数。在这种情况下，这至少是44个字节（假设4个字节int和4个字节的指针）。您应该将此功能更改为以下内容：
// Returns index of item with name `item_name` in the `items` array inside of `cart`. Returns -1 if not found.
int find_item(cart_t *cart, const char* item_name) {
int i;
for(i=0;i<cart->size;++i){
if(strcmp(cart->items[i]->name,item_name) == 0){
return i;
}
}
return -1; // if we get here, then no items were found, so return -1.
// I don't understand your logic in returning 0, since 0 is a valid item index
}
正如@Fang所述，将您的购物车中的商品数量（cart->size）与sizeof(*cart)混淆是整个代码中的常见错误。这需要在您尝试迭代项目的任何地方进行更改。
答案 1 :(得分：2)
代码中导致细分错误的问题出在find_item函数中，您使用的是sizeof关键字，您应该使用购物车的size属性。< / p>
sizeof为您提供购物车结构的大小（以字节为单位）（永远不会更改），而您将购物车中的商品数量存储在size属性中。
这意味着您的功能应该是：
// Returns index of item with name `item_name` in the `items` array inside of `cart`. Returns -1 if not found.
int find_item(cart_t *cart, const char* item_name) {
int i;
for(i=0;i<cart->size;++i){
if(strcmp(cart->items[i]->name,item_name) == 0){
return i;
}
}
if(i == cart->size)
return -1;
return 0;
}