c中的链表（我在这里做错了什么？）

Question

I have this piece of code, and I can't figure out why this isn't working? The inputData() function seems to work, but the print method only prints the first line I send to inputDate() for as many lines that I have inputed.

I'm reading from a file, one line at a time, and putting in to the linked list, that's where the issue is. If I pass values in the code, then there is no problem?

//LINKED LIST
void inputData(char *l)
{
    struct lines *pNewStruct = (struct lines *) malloc(sizeof(struct lines));
    pNewStruct->line = l;

    //inserts if list empty, next set to null
    if(pFirstNode == NULL){
        pNewStruct->next = NULL;
        pFirstNode = pLastNode = pNewStruct;

    } else {

        //inserts if list contains one element
        //this is done to differentiate between first and last node
        if(pFirstNode == pLastNode) {
            pFirstNode->next = pNewStruct;
            pLastNode = pNewStruct;
            pNewStruct->next = NULL;

        //inserts elements when elements in list > 2
        } else {
            pLastNode->next = pNewStruct;
            pNewStruct->next = NULL;
            pLastNode = pNewStruct;

        }
    }
}

void printData()
{
    struct lines *temp = pFirstNode;

    while(temp != NULL)
    {
        printf("%s", temp->line);
        temp = temp->next;
    }
}

Answer 1

For each line you should dynamically allocate new memory and copy the contents of each line into the newly allocated string. Otherwise, if no one keeps track of the memory allocated for these strings, or the strings are on the stack, you run the risk of losing them.

Answer 2

pNewStruct->line = l;

This won't do. And we never see what pFirstNode really is.

So how about using strcpy for copying the char.

Then the two branches in the else. Why do you think you need them. You initiate the pointers while adding the first element. So this pFirstNode->next = pNewStruct;

Is the same in the first case as pLastNode->next = pNewStruct;

So there is not need for another if an else branch in the outer else.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct lines {
  char line [120];
  struct lines *next;
};

struct lines *pFirstNode = NULL;
struct lines *pLastNode = NULL;


//LINKED LIST
void inputData(char *l)
{
    struct lines *pNewStruct = (struct lines *) malloc(sizeof(struct lines));
    strncpy(pNewStruct->line,l,119);


    //inserts if list empty, next set to null
    if(pFirstNode == NULL){
        pNewStruct->next = NULL;
        pFirstNode = pLastNode = pNewStruct;

    } else {
      pLastNode->next = pNewStruct;
      pNewStruct->next = NULL;
      pLastNode = pNewStruct;
    }      
}

void printData()
{
    struct lines *temp = pFirstNode;

    while(temp != NULL)
    {
        printf("%s", temp->line);
        temp = temp->next;
    }
}


int main(void) {
  inputData("one");
  inputData("two");
  inputData("three");
  printData();
  return 0;
}