我有一个问题而且我不确定是什么原因造成的，因为我正在阅读的这本书并没有真正解释恐惧功能，甚至在阅读了这里的一些帖子之后我仍然无法想象发生了什么事。我认为这与将结构读回内存有关
问题在于，当它恢复阵列时，它仍然打印出空白，好像它没有恢复一样，但它声称整个100个部分都已恢复。我倾倒它时只制作了3个结构部件，这可能是个问题吗？
结构有这种形式
#define MAX_PARTS 100
struct part {
int number;
char name[NAME_LEN+1];
int on_hand;
} inventory[MAX_PARTS];
这是函数
void dump(void)
{
FILE *fp;
const char *inv = "inventory.dat";
int chk;
if ((fp = fopen(inv, "wb")) == NULL) {
fprintf(stderr, "Can't open file \"%s\"\n", *inv);
exit(EXIT_FAILURE);
}
chk = fwrite(inventory, sizeof(struct part), MAX_PARTS, fp);
if (feof(fp)) {
fprintf(stderr, "End of file reached\n");
} else if (ferror(fp)) {
fprintf(stderr, "A write error occured\n");
}
fclose(fp);
printf("File has Dumped %d of %d\n", chk, num_parts);
}
void restore(void)
{
FILE *fp;
const char *inv = "inventory.dat";
int chk;
if ((fp = fopen(inv, "rb")) == NULL) {
fprintf(stderr, "Can't open file \"%s\"\n", *inv);
exit(EXIT_FAILURE);
}
chk = fread(inventory, sizeof(struct part), MAX_PARTS, fp);
if (feof(fp)) {
fprintf(stderr, "End of file reached\n");
} else if (ferror(fp)) {
fprintf(stderr, "A read error occurred\n");
}
fclose(fp);
printf("File has restored %d parts\n", chk);
}
其余代码：
/* Maintains a parts database (array version) */
#include <stdio.h>
#include <stdlib.h>
#include "readline.h"
#define NAME_LEN 25
#define MAX_PARTS 100
struct part {
int number;
char name[NAME_LEN+1];
int on_hand;
} inventory[MAX_PARTS];
int num_parts = 0; /* number of parts currently stored */
void dump(void);
void restore(void);
int find_part(int number);
void insert(void);
void search(void);
void update(void);
void print(void);
/**********************************************************
* main: Prompts the user to enter an operation code, *
* then calls a function to perform the requested *
* action. Repeats until the user enters the *
* command 'q'. Prints an error message if the user *
* enters an illegal code. *
**********************************************************/
int main(void)
{
char code;
for (;;) {
printf("Enter operation code: ");
scanf(" %c", &code);
while (getchar() != '\n') /* skips to end of file */
;
switch (code) {
case 'd': dump();
break;
case 'r': restore();
break;
case 'i': insert();
break;
case 's': search();
break;
case 'u': update();
break;
case 'p': print();
break;
case 'q': return 0;
default: printf("Illegal code\n");
}
printf("\n");
}
}
void dump(void)
{
FILE *fp;
const char *inv = "inventory.dat";
int chk;
if ((fp = fopen(inv, "wb")) == NULL) {
fprintf(stderr, "Can't open file \"%s\"\n", *inv);
exit(EXIT_FAILURE);
}
chk = fwrite(inventory, sizeof(struct part), MAX_PARTS, fp);
if (feof(fp)) {
fprintf(stderr, "End of file reached\n");
} else if (ferror(fp)) {
fprintf(stderr, "A write error occured\n");
}
fclose(fp);
printf("File has Dumped %d of %d\n", chk, num_parts);
}
void restore(void)
{
FILE *fp;
const char *inv = "inventory.dat";
int chk;
if ((fp = fopen(inv, "rb")) == NULL) {
fprintf(stderr, "Can't open file \"%s\"\n", *inv);
exit(EXIT_FAILURE);
}
chk = fread(inventory, sizeof(struct part), MAX_PARTS, fp);
if (feof(fp)) {
fprintf(stderr, "End of file reached\n");
} else if (ferror(fp)) {
fprintf(stderr, "A read error occurred\n");
}
fclose(fp);
printf("File has restored %d parts\n", chk);
}
/**********************************************************
* find_part: Looks up a part number in the inventory *
* array. Returns the array index if the part *
* number is found, otherwise, returns -1. *
**********************************************************/
int find_part(int number)
{
int i;
for (i = 0; i < num_parts; i++)
if (inventory[i].number == number)
return i;
return -1;
}
/**********************************************************
* insert: Prompts the user for information about a new *
* part and then inserts the part into the *
* database. Prints an error message and returns *
* prematurely if the part already exists or the *
* database is full. *
**********************************************************/
void insert(void)
{
int part_number;
if (num_parts == MAX_PARTS) {
printf("Database is full; can't add more parts.\n");
return;
}
printf("Enter part number: ");
scanf("%d", &part_number);
if (find_part(part_number) >= 0) {
printf("Part already exists.\n");
return;
}
inventory[num_parts].number = part_number;
printf("Enter part name: ");
read_line(inventory[num_parts].name, NAME_LEN);
printf("Enter quantity on hand: ");
scanf("%d", &inventory[num_parts].on_hand);
num_parts++;
}
/**********************************************************
* search: Prompts the user to enter a part number, then *
* looks up the part in the database. If the part *
* exists, prints the name and quantity on hand; *
* if not, prints an error message. *
**********************************************************/
void search(void)
{
int i, number;
printf("Enter part number: ");
scanf("%d", &number);
i = find_part(number);
if (i >= 0) {
printf("Part name: %s\n", inventory[i].name);
printf("Quantity on hand: %d\n", inventory[i].on_hand);
} else
printf("Part not found.\n");
}
/**********************************************************
* update: Prompts the user to enter a part number. *
* Prints an error message if the part doesn't *
* exist; otherwise, prompts the user to enter *
* change in quantity on hand and updates the *
* database. *
**********************************************************/
void update(void)
{
int i, number, change;
printf("Enter part number: ");
scanf("%d", &number);
i = find_part(number);
if (i >= 0) {
printf("Enter change in quantity on hand: ");
scanf("%d", &change);
inventory[i].on_hand += change;
} else
printf("Part not found.\n");
}
/**********************************************************
* print: Prints a listing of all parts in the database, *
* showing the part number, part name, and *
* quantity on hand. Parts are printed in the *
* order in which they were entered into the *
* database. *
**********************************************************/
void print(void)
{
int i;
printf("Part Number Part Name "
"Quantity on Hand\n");
for (i = 0; i < num_parts; i++)
printf("%7d %-25s%11d\n", inventory[i].number,
inventory[i].name, inventory[i].on_hand);
}
答案 0 :(得分：1)
当你写MAX_PARTS时，它会读取那些记录。因此chk将是MAX_PARTS。
它会给你任何你写的东西。如果您编写了有效的3条记录，那么它应该读取3条有效记录，其他记录将是垃圾记录。
答案 1 :(得分：1)
最基本的调试尝试会显示错误。只需将记录添加到print函数就可以解决问题。
还原时，不要更改num_parts。因此，当您要求打印时，它会打印零件。如果num_parts是您的程序所需数据的一部分，那么它也需要保存/恢复。或者，只写出已填充的部件数量，并将恢复功能中的num_parts设置为读取的部件数量。