c-从链接列表中删除元素

Question

假设我有下面的列表：

List of CDData
1: Test1
2: Test2
3: Test3
4: Test4
5: Test5
6: Test6

现在我想使用链表从列表中删除第三个：这意味着free(removeFromDList(3((；这是我的功能：

TCD *removeFromDList(int res)
{
int count = 0;
TCD *CDData = First;
CDData->Prev = First;
if (First == NULL)
{
printf("Errorn");
return NULL;
}
while (CDData)
{
count++;
if (count == res)
{
if (count == 1)
{
if (CDData == Last)
Last = NULL;
First = First->Next;
return CDData;
}
else
{
while (CDData != NULL)
{
CDData->Prev = CDData->Next;
if (CDData == Last)
Last = CDData->Prev;
// printf("%s",CDData->Title) I tested here whether my function is going to 
//  delete the third one or not with the printf() and it's actually printing the third one 
// Which means it's correct 

return CDData;
}
}
}
else
CDData->Prev = CDData;
CDData = CDData->Next;
}
}

顺便说一句，这就是TCD 的定义

typedef struct F
{
char *Title;
struct F *Next;
struct F *Prev;
}TCD;

现在，在重新打印我的列表后，似乎所有的CDData(整个数据结构(都被释放了。有什么想法吗？

我把它作为输出

List of CDData

Answer 1

我认为在这个结构定义中

typedef struct F
{
char *Titel;
struct F *Next;
struct F *Prev;
}TCD;

您的意思是第一个数据成员的名称是CCD_ 1而不是CCD_。

您需要为该数据成员将指向的字符串动态分配内存。

函数可以调用未定义的行为，至少因为最初全局变量First(顺便说一句，当函数依赖于全局变量时，这是个坏主意(可以等于NULL。所以在这个代码片段

TCD *CDData = First;
CDData->Prev = First;

存在使用空指针(CDData->Prev(来访问存储器的尝试。

这个内部while循环

while (CDData != NULL)
{
CDData->Prev = CDData->Next;
if (CDData == Last)
Last = CDData->Prev;
// printf("%s",CDData->Title) I tested here whether my function is going to 
//  delete the third one or not with the printf() and it's actually printing the third one 
// Which means it's correct 

return CDData;
}

没有道理。

请注意，在C中，索引从0开始。

使用您的方法，函数可以按照以下方式编写，如下面的演示程序所示。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct F
{
char *Title;
struct F *Next;
struct F *Prev;
} TCD;
TCD *First, *Last;
TCD * removeFromDList( size_t n )
{
TCD **Current = &First;

while ( *Current && n--)
{
Current = &( *Current )->Next;
}

TCD *target = *Current;

if ( *Current )
{
if ( ( *Current )->Next == NULL ) 
{
Last = ( *Current )->Prev;  
}
else
{
( *Current )->Next->Prev = ( *Current )->Prev;
}

*Current = ( *Current )->Next;
}

return target;
}
int append( const char *s )
{
TCD *Current = malloc( sizeof( TCD ) );
int success = Current != NULL;

if ( success )
{
Current->Title = malloc( strlen( s ) + 1 );
success = Current->Title != NULL;

if ( success )
{
strcpy( Current->Title, s );
Current->Prev = Last;
Current->Next = NULL;
}
else
{
free( Current );
}
}

if ( success )
{
if ( Last )
{
Last = Last->Next = Current;
}
else
{
First = Last = Current;
}
}

return success;
}
FILE * display( FILE *fp )
{
for ( TCD *Current = First; Current; Current = Current->Next )
{
fprintf( fp, "%s -> ", Current->Title );
}

fputs( "NULL", fp );

return fp;
}
int main(void) 
{

for ( char s[] = "A"; s[0] != 'E'; ++*s )
{
append( s );
}


fputc( 'n', display( stdout ) );

TCD *p = removeFromDList( 3 );
free( p->Title );
free( p );
fputc( 'n', display( stdout ) );

p = removeFromDList( 1 );
free( p->Title );
free( p );
fputc( 'n', display( stdout ) );

p = removeFromDList( 0 );
free( p->Title );
free( p );
fputc( 'n', display( stdout ) );

p = removeFromDList( 0 );
free( p->Title );
free( p );
fputc( 'n', display( stdout ) );

printf( "First == NULL : %d, Last == NULL : %dn", First == NULL, Last == NULL );
return 0;
}

程序输出为

A -> B -> C -> D -> NULL
A -> B -> C -> NULL
A -> C -> NULL
C -> NULL
NULL
First == NULL : 1, Last == NULL : 1