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Question

我的代码应该找到产品 ID、名称、数量和价格。 输入产品 ID 时，应打印产品 ID 所在的整行。

文本文件包含此输入：

1 CADBURY 999 1.900000
2 PEPSI 999 2.500000
3 IPHONE 976 2500.000000
4 SPIRULINA 100 50.000000

代码已使用输入“4”进行编译。但是输出是循环的：

Please enter product ID :

它没有读取“4”的整行。

代码如下：

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

int addProduct();

struct product
{
    int quantity, reorder, i, id;
    char name[20];
    float price;
};

int secondmain()
{
    FILE * fp;

    int i=0;
    struct product a;
    system("cls");

    char checker;



    do
    {
        fp = fopen("addproduct.txt","a+t");
        system("cls");

        printf("Enter product ID : ");
        scanf(" %d", &a.id);

        printf("Enter product name : ");
        scanf(" %s", a.name);

        printf("Enter product quantity : ");
        scanf(" %d", &a.quantity);

        printf("Enter product price : ");
        scanf(" %f", &a.price);


        fprintf(fp, "%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);
        printf("Record saved!\n\n");

        fclose(fp);

        printf("Do you want to enter new product? Y / N : ");

        scanf(" %c", &checker);
        checker = toupper(checker);

        i++;

        system("cls");
    }
    while(checker=='Y');



    if(checker == 'N')
        {
        fp = fopen("addproduct.txt","r");

        while(fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price)==4)
            {
        fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price);
        printf("%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);
            }

        fclose(fp);

        }


return(0);
}

/*-------------- ERROR START HERE-----------------*/

int main()
{
FILE * fp;
system("cls");
struct product a;
char array[255];
int productID;

fp = fopen("addproduct.txt","r");

while(1){
fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price);

productID = atoi(array);

printf("Please enter product ID : ");
scanf(" %d", &productID);

if(productID == a.id)
    {
    fgets(array, 255, (FILE*)fp);
    printf("%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);

    }

    }
return(0);
}

Answer 1

while (fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price) == 4)
{
    fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price);
    printf("%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);
}

您调用fscanf 两次，它会跳过每第二行。

fgets(array, 255, (FILE*)fp);
printf("%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);

这部分是将行读入文本。然后它应该使用sscanf 或strtok 来解析行。

您可能还必须刷新标准输入，否则 scanf(" %c", &checker) 可能无法正常工作。它使事情更容易分解为功能。示例：

int find_item_by_id(const char* fname, int find_id)
{
    int found = 0;
    struct product a;
    FILE *fp = fopen(fname, "r");
    if (fp)
    {
        while (fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price) == 4)
        {
            if (a.id == find_id)
            {
                found = 1;
                break;
            }
        }
        fclose(fp);
    }

    return found;
}

void add_item(const char* fname)
{
    struct product a;
    printf("Enter product ID : ");
    scanf(" %d", &a.id);

    printf("Enter product name : ");
    scanf(" %s", a.name);

    printf("Enter product quantity : ");
    scanf(" %d", &a.quantity);

    printf("Enter product price : ");
    scanf(" %f", &a.price);

    if (find_item_by_id(fname, a.id) != 0)
    {
        printf("item already exists\n");
        return;
    }

    FILE *fp = fopen(fname, "a+");
    if (fp)
    {
        fprintf(fp, "%d %s %d %.2f\n", a.id, a.name, a.quantity, a.price);
        fclose(fp);
    }
}

int main()
{
    const char* filename = "c:\\test\\_test.txt";

    printf("list:\n");
    struct product a;
    FILE *fp = fopen(filename, "r");
    if (fp)
    {
        while (fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price) == 4)
            printf("%d %s %d %f\n", a.id, a.name, a.quantity, a.price);
        fclose(fp);
    }

    while(1)
    {
        add_item(filename);

        printf("Add nother item? (y/n)\n");
        int result;
        while (1)
        {
            result = getchar();
            if (result == 'y' || result == 'n')
                break;
        }
        if (result != 'y')
            break;
    }

    return 0;
}