c-如何使用结构数组根据用户输入输出给定的结构

Question

问题：我正在尝试用beer.dat中的数据填充我的beerDatastruct，只是我不了解结构如何在不破坏代码的情况下很好地实现。我想我需要一个结构数组。

beer.dat文件内容：

7 // total number of beers 
Coors //beer name
1234567 // beer id
72 // beer quantity
7.40 //beer price 
Miller
7777777
44
9.70
Bud
7654321
345
9.90
Wachusett
7799435
4
14.70
Corona
9999999
112
9.99
Zima
0000000
1
0.01
Mikes
0890398
12
10.99

代码：

/*
User interface, alloc, malloc 13 points
Correct structure and array built 7 points
Recursive sort
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct beerData {
char *beer[7]; // number of brands
char *beer_name; //names
int beer_id[7]; //ID number given to beer
int beer_quantity; //stock
float beer_price; // pricing
} beer_data;

void printStr(char *line) {
char *look = "";
printf("What would you like to search for? n");
scanf("%s", look);
//printf("Line: %sn", line);

exit(0);
}
void search() {
//look through beer.dat for a specific beer by ID number.
char str[32];
FILE *fp = fopen("beer.dat", "r");
if (fp == NULL) {
printf("Error: can't open file to readn");
} else {
while (!feof(fp)) {
fscanf(fp, "%s ", str);
//printf("%sn",str);
printStr(str);
}
}
fclose(fp);
}

int main() {
int user_choice;
printf("Enter 1 to search for a beer, 2 to view the entire catalogue,"
" and 3 to place an order, press 4 to exit.n");

while (user_choice != 4) {
scanf("%d", &user_choice);
switch (user_choice) {
case 1:
printf("Searching for a beern");
user_choice = 0;
search();
break;
case 2:
printf("Viewing Inventoryn");
//viewInv();
break;
case 3:
printf("Placing an order...n");
//placeOrder();
break;
case 4:
printf("Goodbye!n");
exit(0);
default:
printf("Incorrect entry, try again.n");
continue;
}
}

}

我正在尝试创建一个函数来搜索文件，并根据给定的ID找到一个特定的啤酒，该ID在一个应该是其结构的集合中。。。因此，一旦输入了ID，程序就会搜索啤酒，并打印出名称、ID、数量和价格。

为了完全清楚起见，我会发布作业问题，以防我没有正确传达我的需求。任务是：

1. 搜索啤酒时应提示用户输入身份证号码，如果啤酒在您的库存中，则结果应显示其数量和价格
2. 整个库存的视图将按价格升序显示所有啤酒及其ID号、价格和数量。此排序应使用Recursive Bubble或Recursive Selection排序来完成
3. 下订单时，应将订单的发票打印到屏幕上

Answer 1

首先需要声明一个有意义的结构。该结构包含每个项目的相关信息。示例：

typedef struct beer_data 
{
char name[20]; //names
int id; //ID number given to beer
int quantity; //stock
float price; // pricing
} beer_data;

接下来，您需要一个这种结构的数组。使用malloc为total数量的项目分配足够的内存。示例：

beer_data *beers = malloc(total * sizeof(beer_data));

现在您有了beers[0], beers[1], beers[2]...，读取文件中的每一项并将其放入结构中。

要读取文件，可以使用fscanf或fgets。

文件中的第一行是

7 // total number of beers 

您可以使用fscanf:读取数字7

int maximum = 0;
fscanf(fp, "%d", &maximum);

这应该很好，但之后还有一些你不感兴趣的字符。使用fgets读到行尾并丢弃这些字符。

开始一个循环，阅读每一行，添加到结构中。

使用此方法，如果要添加新项目，则必须增加内存大小。参见使用realloc的add_item。这可能太先进了。或者，您可以将新项目保存到文件中，调用free(beers)，然后再次读取该文件。

typedef struct beer_data 
{
char name[20]; //names
int id; //ID number given to beer
int quantity; //stock
float price; // pricing
} beer_data;
void search_by_name(beer_data *beers, int total)
{
char buf[20];
printf("Enter name to search: ");
scanf("%19s", buf);
//note, we put %19s because beers[count].name is only 20 bytes long
for(int i = 0; i < total; i++)
{
if(strcmp(beers[i].name, buf) == 0)
{
printf("Found: %s, %d, %d, %.2fn",
beers[i].name, beers[i].id, beers[i].quantity, beers[i].price);
return;
}
}
printf("%s not foundn", buf);
}
void print_list(beer_data *beers, int total)
{
for(int i = 0; i < total; i++)
{
printf("%s %d %d %.2fn",
beers[i].name, beers[i].id, beers[i].quantity, beers[i].price);
}
}
void add_item(beer_data *beers, int *total)
{
//note, total has to be passed as pointer 
//because we are changing it
//allocate more memory:
beers = realloc(beers, sizeof(beer_data) * (*total + 1));
printf("enter name: "); 
scanf("%19s", beers[*total].name);
printf("enter id:");
scanf("%d", &beers[*total].id);
printf("enter quantity:");
scanf("%d", &beers[*total].quantity);
printf("enter price:");
scanf("%f", &beers[*total].price);
//increase the total
*total += 1;
}
int main() 
{
FILE *fp = fopen("beer.dat", "r");
if(!fp)
{
printf("Error: can't open file to readn");
return 0;
}
char buf[500];
int maximum = 0;
fscanf(fp, "%d", &maximum);
//read the rest of the line and discard it 
fgets(buf, sizeof(buf), fp);
//allocate memory
beer_data *beers = malloc(maximum * sizeof(beer_data));
int total = 0;
while(1)
{
fgets(buf, sizeof(buf), fp);
sscanf(buf, "%19s", beers[total].name);
if(fscanf(fp, "%d", &beers[total].id) != 1) break;
fgets(buf, sizeof(buf), fp);
if(fscanf(fp, "%d", &beers[total].quantity) != 1) break;
fgets(buf, sizeof(buf), fp);
if(fscanf(fp, "%f", &beers[total].price) != 1) break;
fgets(buf, sizeof(buf), fp);
total++;
if(total == maximum)
break;
}
fclose(fp);
int stop = 0;
while (!stop)
{
printf("
Enter 0 to exitn
Enter 1 print listn
Enter 2 for searchn
Enter 3 add new itemn");
int choice;
scanf("%d", &choice);
switch(choice)
{
case 0: 
stop = 1;
break;
case 1:
print_list(beers, total);
break;
case 2:
search_by_name(beers, total);
break;
case 3:
add_item(beers, &total);
break;
}
printf("n");
}
//cleanup:
free(beers);
return 0;
}