[英]Problems with Linked List of String in C
I'm trying to make a minishell and store all the commands the user types, and when the user enters history
it should display all the commands the user has typed so far, and when the user types history -c
then it should clear the linked list.我正在尝试制作一个 minishell 并存储用户输入的所有命令,当用户输入
history
它应该显示用户迄今为止输入的所有命令,当用户输入history -c
时,它应该清除链接列表。
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <errno.h>
#include <signal.h>
#include <sys/wait.h>
typedef struct node
{
char* data;
struct node *next;
} node;
node *create_node(char* data)
{
node *ptr = malloc(sizeof(node));
if (ptr == NULL)
{
fprintf(stderr, "Error: Out of memory in create_node()\n");
exit(1);
}
ptr->data = data;
ptr->next = NULL;
return ptr;
}
node *insert_node(node *head, char* data)
{
node *temp;
if (head == NULL)
return create_node(data);
temp = head;
while (temp->next != NULL)
{
temp = temp->next;
}
// 'temp' is pointing to the last node in the list now.
temp->next = create_node(data);
return head;
}
void print_list(node *head)
{
node *temp;
if (head == NULL)
{
printf("(empty list)\n");
return;
}
for (temp = head; temp != NULL; temp = temp->next)
printf("%s%c", (char*)temp->data, '\n');
}
int main (int argc, char ** argv)
{
char buf[1024];
char * args[MAX_ARGS];
char ** arg;
node *head = NULL;
while (1)
{
printf("#");
if (fgets (buf, 1024, stdin ))
{
head = insert_node(head, buf);
arg = args;
*arg++ = strtok(buf, SEPARATORS); // tokenize input
while ((*arg++ = strtok(NULL, SEPARATORS)));
if (args[0])
{
//#byebye command, exist the while loop.
if (!strcmp(args[0], "byebye")) {
break;
}
if (!strcmp(args[0], "history"))
{
// command history with flag c
if (args[1] && !strcmp(args[1], "-c"))
{
// clear the linked list
}
else
{
print_list(head);
printf("\n");
}
continue;
}
arg = args;
while (*arg) fprintf(stdout, "%s ", *arg++);
fputs ("\n", stdout);
}
}
}
return 0;
}
But this is my output:但这是我的输出:
#hello hello #adding adding #to list to list #history history history history history
So, instead of printing out all the commands, it prints out history
and I don't know what I am doing wrong.因此,它不是打印出所有命令,而是打印出
history
而我不知道我做错了什么。 Please help, it has been awhile since I touched C and pointers.请帮助,我已经有一段时间没有接触 C 和指针了。
Your create_node()
is implemented wrong.您的
create_node()
实现错误。
You are leaking the memory you malloc()
for the node::data
member, as you are immediately re-assigning the node::data
to point at the same memory that the input char*
parameter is pointing at, thus losing the malloc
'ed memory.您正在为
node::data
成员泄漏malloc()
内存,因为您立即重新分配node::data
以指向输入char*
参数所指向的同一内存,从而丢失了malloc
' ed 记忆。
As such, all of your created nodes end up pointing at the same char[]
buffer in main()
, which is being reused for every string the user types in.因此,您创建的所有节点最终都指向
main()
中的同一个char[]
缓冲区,该缓冲区被用户输入的每个字符串重复使用。
create_node()
needs to make a copy of the char
data, which is probably what you intended to do, but didn't do so correctly. create_node()
需要复制char
数据,这可能是您打算做的,但没有正确执行。 Try this:尝试这个:
node *create_node(char* data)
{
node *ptr = malloc(sizeof(node));
if (ptr == NULL)
{
fprintf(stderr, "Error: Out of memory in create_node()\n");
exit(1);
}
ptr->data = strdup(data);
ptr->next = NULL;
if (ptr->data == NULL)
{
fprintf(stderr, "Error: Out of memory in create_node()\n");
free(ptr);
exit(1);
}
return ptr;
}
And then you need to add a new function to free each node and its data
when you are done using it, eg:然后你需要添加一个新函数来在你使用完每个节点后释放它的
data
,例如:
node* free_node(node* n)
{
node *next = n->next;
free(n->data);
free(n);
return next;
}
...
int main (int argc, char ** argv)
{
node *head = NULL;
...
while (head != NULL) {
head = free_node(head);
}
return 0;
}
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