调用函数

Question

好的，所以我得到了一个文本文件，里面有一堆id，size和weights.the抓住这些数据的函数位于底部的void listBoxes（const char filename []）。如果用户输入1，它应该列出文本文件中的所有信息以及我输入的一些标题。当我在我的主要情况1中调用该函数时，它只打印标题，并且在尝试打印实际数据时发生错误。我知道我只是部分正确地调用了函数，但我不确定如何从函数中获取数据。

// Workshop 9 - Files
// Name:
// Student #:

#include <stdio.h>

struct Box 
{
    int id;        // the box ID
    double size[3];   // dimensions of the box (Length, Width, Height)
    double weight; // weight of the box
};

void printBox(struct Box b) 
{
    printf("\nID:     %6d\n"
            "Length: %6.2lf\n"
            "Width:  %6.2lf\n"
            "Height: %6.2lf\n"
            "Weight: %6.2lf\n\n", b.id, b.size[0], b.size[1], b.size[2], b.weight);
}

int menu(void)
{
    int choice = -1;

    printf("1- List all boxes\n");
    printf("2- Find a box\n");
    printf("3- Add a box\n");
    printf("4- Randomly pick a lucky box!\n");
    printf("0- Exit program\n");

    printf("Select an option: ");
    do 
    {
        scanf("%d", &choice);
        if (choice < 0 || choice > 4)
            printf("Please enter a number between 0 and 4: ");
    } while (choice < 0 || choice > 4);
    return choice;
}

int main(void) 
{
    struct Box b;

    FILE * fp = NULL;

    int choice; // , boxID, r;

    char filename[] = "storage.txt";

    printf("Welcome to My Storage Room\n");
    printf("==========================\n");
    do {
        // get user's choice
        choice = menu();

        switch (choice) {
            case 1:
                // IN_LAB: list items
                listBoxes(filename);
                break;

            case 2:
                // IN_LAB: find a box given its ID
                // ask for ID

                // call displayBox

                break;

            case 3:
                // AT_HOME: add a box
                // get user input for box's ID, size and weight

                // call addBox, print message to show number of boxes added

                break;

            case 4:
                // AT_HOME: randomly pick a lucky box

                // choose a random number between 1 and the number of boxes in storage
                // display the lucky box!

                break;
        };

    } while (choice > 0);

    return 0;
}

void listBoxes(const char filename[])
{
    struct Box b;

    FILE * fp = NULL;

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

    if (fp != NULL)
    {
        printf("List of boxes\n");
        printf("=============\n");
        printf("ID Length Width Height Weight\n");
        printf("-----------------------------\n");
        fscanf("%2d %6.2lf %5.2lf %6.2lf %6.2lf\n", &b.id, &b.size[0],  &b.size[1], &b.size[2], &b.size[3], &b.weight);
        fclose(fp);
    }
    else
    {
        printf("Error opening file\n");
    }
    return 0;
}

Answer 1

与listBoxes()功能相关的问题是由于使用fscanf()功能不正确造成的。正确使用手册页中给出的fscanf()：

int fscanf(FILE *stream, const char *format, ...);

您尚未指定要从中读取输入的文件指针。此外，您还提供了仅由格式化打印功能使用的格式信息，并引用了不存在的b.size[]的额外索引。正确的用法是：

fscanf(fp, "%d %lf %lf %lf %lf\n", &b.id, &b.size[0], &b.size[1], &b.size[2], &b.weight);

您还没有真正打印读入的信息，因此您应该以您希望的格式进行此操作。

最后，您无需return来自void函数的值。