c - 在 C 中，将指向结构的指针值发送到函数时返回 float 会更改结构的值

Question

我正在尝试使用 C 语言中的结构和指向结构的指针进行一些练习。我遇到了一个困扰我的问题。我已经设置了一个函数，该函数从指向结构的指针获取 3 个值并返回一个 float 。然而，当调用这个函数时，它修改了原始结构的值，最终导致访问冲突和一些令人讨厌的字符反流。单步执行代码后，值没问题，直到我返回函数的值。

这是我的结构:

struct product
{
    int ID;
    char name[MAXNAME];
    char department[MAXDEPT];
    float price;
    int taxable;
    int free_shipping_eligible;
};
typedef struct product Product;

函数原型(prototype):

Product * getInput(void);
float transactionTotal(const float price, const int taxable,
const int free_shipping);
void displayTransaction(const Product * inventory,
const float total_price);

主要内容:

int main(void)
{
    // Declare a pointer to a struct.
    Product * invPoint = NULL;
    float grand_total = 0.0;

    // Get the value of the address of a struct.
    invPoint = getInput();

    // Use that address to get the total of a transaction.
    grand_total = transactionTotal(invPoint->price, invPoint->taxable,
        invPoint->free_shipping_eligible);

    // Display product information and the transaction's total.
    displayTransaction(invPoint, grand_total);
    return EXIT_SUCCESS;
}

这是填充结构成员值的函数:

Product * getInput(void)
{
    // Declare our struct and struct pointer variables.
    Product inventory;
    Product * fillInventory = NULL;

    // Get user input.
    printf("Please enter the product's ID.\n\t");
    scanf("%d", &inventory.ID);
    printf("Please enter the product's name.\n\t");
    scanf("%s", &inventory.name);
    printf("Please enter the product's price.\n\t");
    scanf("%f", &inventory.price);
    printf("Which department is the product located in?\n\t");
    scanf("%s", &inventory.department);
    printf("Is it taxable?  0 for no, 1 for yes.\n\t");
    scanf("%d", &inventory.taxable);
    printf("Is it free shipping eligible?  1 for no, 0 for yes.\n\t");
    scanf("%d", &inventory.free_shipping_eligible);
    fillInventory = &inventory;

    // Return a pointer to our struct.
    return fillInventory;
}

transactionTotal 函数似乎是罪魁祸首。这是它的代码:

float transactionTotal(const float price, const int taxable,
const int free_shipping)
{
    float total_price = 0.00;
    float tax = (float)(taxable * TAX_RATE);
    float shipping = (float)(free_shipping * SHIPPING_RATE);
    total_price = price + price * tax + price * shipping;
    return total_price;
}

在开始上述功能之前，我输入了以下值:

编号:232

名称:“咖啡”

部门:“食品”

价格:8.99

应税:0

free_shipping_eligible:1

transactionTotal 函数之后:

编号:-858993460

姓名:(奇怪的字符)

部门:(奇怪的字符)

价格:9.88899994

应税:-858993460

free_shipping_eligible:14679252

Answer 1

    // Return a pointer to our struct.
    return fillInventory;
}

你的结构对象是在你的函数中声明的，并且有一个在你的函数返回后结束的生命周期。当您的函数返回时结构对象被丢弃，之后尝试访问它会调用未定义的行为。将您的结构对象作为参数传递给函数或使用 malloc 分配其存储空间以解决您的问题。