c-链表输出

Question

我正在做一项学校作业，几个月前我才开始学习C编程。在这个作业中，我要输出一个"文件"所占用的空间。

初始输出是正确的，但是，当我尝试打印出一个表时，输出会变得不正确。

代码：

#define TOTAL_DISK_BLOCKS 32
#define TOTAL_DISK_INODES 8
int blockStatus[TOTAL_DISK_BLOCKS];                   // free = 0
int blockList[TOTAL_DISK_BLOCKS - TOTAL_DISK_INODES]; // list of blocks of a file
struct file_table
{
char fileName[20];
int fileSize;
struct block *sb; // start block
};
struct file_table fileTable[TOTAL_DISK_BLOCKS - TOTAL_DISK_INODES];
struct block
{
int blockNumber;
struct block *next;
} * head;
int AllocateBlocks(int Size)
{
int i = 0, count = 0, inList = 0, nextBlock = 0, j = 0, dcount = 0, fails = 0;
int allocStartBlock = TOTAL_DISK_INODES;
int allocEndBlock = TOTAL_DISK_BLOCKS - 1;
// check whether sufficient free blocks are available
// some codes here     
{
for (j = 0; j < Size; j++)
{
nextBlock = (rand() % (allocEndBlock - allocStartBlock + 1)) + allocStartBlock;
if (blockStatus[nextBlock] == 0)
{
// printf("ncount:%dn", count);
blockList[j] = nextBlock;
count += 1;
}
else
{
count = 0;
fails += 1;
// printf("nfails:%d, block %d takenn", fails, nextBlock);
break;
}
}
}
// remaining blocks left
dcount = 0;
for (i = 0; i < (TOTAL_DISK_BLOCKS - TOTAL_DISK_INODES); i++)
if (blockStatus[i] == 0)
dcount++;
printf("Remaining blocks: %dn", dcount);
if (count == Size)
{
for (j = 0; j < Size; j++)
{
blockStatus[blockList[j]] = 1;
}
return 0; // success
}
else
return 1; // not successful
}
void printBlockNumbers(struct block *temp)
{
// Return if list is empty
if (head == NULL)
{
printf("List is empty.");
return;
}
temp = head;
while (temp != NULL)
{
printf("-%d", temp->blockNumber); // Print data of current node
temp = temp->next;                // Move to next node
}
}
void main()
{
int i = 0, j = 0, numFiles = 0, nextBlock = 0, ret = 1;
char s[20];
struct block *temp, *newBlock;
//some print codes here...
scanf("%d", &numFiles);
for (i = 0; i < numFiles; i++)
{
printf("nEnter the name of file #%d: ", i + 1);
scanf("%s", fileTable[i].fileName);
printf("Enter the size (kB) of file #%d: ", i + 1);
scanf("%d", &fileTable[i].fileSize);
ret = AllocateBlocks(fileTable[i].fileSize);
if (ret == 0)
{
head = (struct block *)malloc(sizeof(struct block));
head->blockNumber = blockList[0];
head->next = NULL;
temp = head;
for (j = 1; j < fileTable[i].fileSize; j++)
{
newBlock = (struct block *)malloc(sizeof(struct block));
newBlock->blockNumber = blockList[j]; // Link data field of newNode
newBlock->next = NULL;                // Make sure new node points to NULL
temp->next = newBlock; // Link previous node with newNode
temp = temp->next;     // Make current node as previous node
}
printf("Blocks occupied");
printBlockNumbers(fileTable[i].sb);
printf("nFile allocation successn");
}
else
{
printf("nFile allocation failedn");
}
}
// Seed the pseudo-random number generator used by rand() with the value seed
srand(1234);
printf("nFile Allocation Tablen");
printf("%s%20s%40sn", "FILE_NAME", "FILE_SIZE", "BLOCKS_OCCUPIED");
for (i = 0; i < numFiles; i++)
{
printf("%s%20d", fileTable[i].fileName, fileTable[i].fileSize);
printf("tttt");
printBlockNumbers(fileTable[i].sb);
printf("n");
}
printf("File allocation completed. Exiting.n");
}

下面是第一个输出。

Blocks occupied-15-30-17
Blocks occupied-21-10-27-10
Blocks occupied-20-26-12-24-19

这就是表的输出。

File Allocation Table
FILE_NAME           FILE_SIZE                         BLOCKS_OCCUPIED
3                   3                           -20-26-12-24-19
4                   4                           -20-26-12-24-19
5                   5                           -20-26-12-24-19
File allocation completed. Exiting.

Answer 1

在第一个循环中，您每次都打印新分配的列表，但在第二个循环中您打印最后分配的列表时，您从列表中打印，该列表的尾部是全局变量head。

在这里：

void printBlockNumbers(struct block *temp)
{
// Return if list is empty
if (head == NULL)
{
printf("List is empty.");
return;
}
temp = head;

温度的初始值无关紧要。

此处：

head = (struct block *)malloc(sizeof(struct block));
head->blockNumber = blockList[0];
head->next = NULL;
temp = head;

您正在分配head的temp值，因此temp->smth指向与head->smth相同的地址，因此当您使用printBlockNumbers打印head时，它将打印出在该循环中分配给它的内容。

您应该将printBlockNumbers更改为：

void printBlockNumbers(struct block *temp)
{
// Return if list is empty
if(!temp) {
return;
}

while (temp != NULL)
{
printf("-%d", temp->blockNumber); // Print data of current node
temp = temp->next;                // Move to next node
}

并且还在每个循环中分配CCD_ 10的CCD_。

FYI：如果你想传递一些东西作为"；引用"；(即指针(为了能够更改此函数中的原始值，您可以这样做：

void changeIntToFive(int* a) {
*a = 5;
}
int main(){
int var = 1;
changeIntToFive(&var);
printf("%dn", var);    // prints 5
}

如果你想对指针做同样的事情：

int glob = 5;
void makePtrPointToGlob(int** a) {
*a = &glob;
}
int main(){
int *ptr;
makePtrPointToGlob(&ptr);
printf("%dn", *ptr);    // prints 5
}