c - 在 C 中使用文件中的库存数据时，数据打印不正确

Question

我目前正在开发一个程序，该程序获取 5 种产品的数量和价格并将其写入文本文件，以表格的形式打印整个数据，然后打印所选价格之一。但是，它仅将最后一个产品的数据写入打印表，并且所选产品的价格打印 0。

#include <stdio.h>
#include <stdlib.h>

typedef struct Stock {
    int quantity;
    float price;
};
void print_stock(Stock a, int len) {
    for (int code = 0; code < len; code++)
        printf("code[%d] %4f %4d\n", code, a.price, a.quantity);
}

int main() {
    FILE *fp = fopen("stocks.txt", "w+");
    Stock a;
    if (fp == NULL) {
        puts("File couldn't be opened.\n");
        exit(1);
    }
    int code, c;
    char arr_code[5];
    int len = sizeof(arr_code) / sizeof(arr_code[0]);
    int option;
    printf("There will be %d product(s) in the stock.\n", len);
    for (code = 0; code < len; code++) {
        printf("Enter the product's quantity:");
        scanf("%d", &a.quantity);
        printf("Enter the product's price:");
        scanf("%f", &a.price);
        fprintf(fp, "quantity-%7d price-%7f\n", a.quantity, a.price);
    }
    print_stock(a, len);

    fclose(fp);

    FILE *fp2 = fopen("stocks.txt", "r");
    printf("Enter an option(starts from 0):\n");
    scanf("%d", &option);
    fseek(fp2, option * sizeof(struct Stock), SEEK_SET);
    fread(&a, sizeof(struct Stock), 1, fp2);
    printf("the price is %f\n", a.price);

    fclose(fp2);
}

我期望输出是这样的:

    There will be 5 product(s) in the stock.
    Enter the product's quantity:76
    Enter the product's price:88
    Enter the product's quantity:5
    Enter the product's price:44
    Enter the product's quantity:89
    Enter the product's price:32
    Enter the product's quantity:54
    Enter the product's price:33
    Enter the product's quantity:94
    Enter the product's price:65
    code[0] 88.000000   76
    code[1] 44.000000   5
    code[2] 32.000000   89
    code[3] 33.000000   54
    code[4] 65.000000   94
    Enter an option(starts from 0):
    2
    the price is 32.000000

但我得到这个结果:

    There will be 5 product(s) in the stock.
    Enter the product's quantity:76
    Enter the product's price:88
    Enter the product's quantity:5
    Enter the product's price:44
    Enter the product's quantity:89
    Enter the product's price:32
    Enter the product's quantity:54
    Enter the product's price:33
    Enter the product's quantity:94
    Enter the product's price:65
    code[0] 65.000000   94
    code[1] 65.000000   94
    code[2] 65.000000   94
    code[3] 65.000000   94
    code[4] 65.000000   94
    Enter an option(starts from 0):
    3
    the price is 0.000000

Answer 1

到目前为止，您正在多次打印 a 的最新内容。

只需将 len 传递为 1，将 print_stock 函数调用移动到 for 循环内即可。

for (code = 0; code < len; code++) {
    printf("Enter the product's quantity:");
    scanf("%d", &a.quantity);
    printf("Enter the product's price:");
    scanf("%f", &a.price);
    fprintf(fp, "quantity-%7d price-%7f\n", a.quantity, a.price);

    print_stock(a, 1);
}

此外，打印时还应该考虑索引。

void print_stock(Stock a[], int len) {
    for (int code = 0; code < len; code++)
        printf("code[%d] %4f %4d\n", code, a[code].price, a[code].quantity);
}