C 在链表add函数中传递值

在过去的2.5个小时里，我一直在创建这个链表，并试图理解为什么它没有将内存地址传递给链表的开头。在我开始学习java中的数据结构之前，我试图理解C中的链表。我研究了其他问题，我不明白为什么它不起作用。请原谅我的评论，我一直在努力理解一切。提前感谢您的时间和帮助

head变量在新赋值后等于NULL head=addFamMember（空）；在主线程中。但我可以通过打印add函数的成员（名称、年龄和下一个指针）看到内存已在add函数中分配。以下是输出：

Enter command to add, print, or quit: add
Enter name and age: brett 28
Added:brett Age:28 POINTING to:(null) 


Enter command to add, print, or quit:

代码是这样的：我留下他的评论可能有助于描述我的想法，并指出我错在哪里

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

typedef struct S_Family{
    char name[16];
    int age;
    struct S_Family *next;
}Family;

//prototypes
Family *addFamMember (Family *previous);
void CleanUp(Family *start);
void PrintList(Family *start);

int main(){
    setvbuf(stdout, NULL, _IONBF, 0);

    printf("Enter command to add, print, or quit: ");

    char input[16]; //fgets var to store input
    char command[16]; //sscanf var to store read info from input

    Family *head = NULL; //For a linked list we need to set up the first node and point it NULL
    Family *newest = NULL; //We also need a pointer dedicated to updating the latest created node

    //This while loop will continue to get input until the command "quit" is typed 
    //It includes the functionality of printing the list and adding new nodes
    while( fgets(input, 15, stdin)){
        sscanf(input, "%s", command);

        if ( strcmp(command, "quit") == 0) {
            printf("\n\nBreaking.........");
            break;

        } else if ( strcmp(command, "print") == 0) {
            PrintList(head);

        } else if ( strcmp(command, "add") == 0) {
            if ( head = NULL){
                head = addFamMember(NULL); //If there are no nodes give head a memory address so now we do (recursion somewhat?)
                printf("head:%s ", head->name); //this doesn't print!! Head = NULL above for some reason.
                newest = head; //newest cannot stay equal to NULL. this allows us to pass it as a param to add function w/out the start being NULL anymore              
                printf("newest:%s ", newest->name);
            } else {
                newest = addFamMember(newest); //Recursion where the new node gets a mem address and gets the previous node as guide to cont. the list
            }                                  //now we go to the add function
        }
        printf("\nEnter command to add, print, or quit: ");
    }

    CleanUp(head);

    return 0;
}

/*We want to return a new family member structure
so we start of with a Family return type. The param
as mentioned before needs to be a pointer to the address
of the previous node. That node will be pushed away from the
NULL in a singly or doubly linked list */
Family *addFamMember (Family *previous) { 


    /*Now we need to get the member variable info for that newFamMember
    and store into the newly created data structure newFamMember*/
    char input[16];

    printf("Enter name and age: ");

    fgets(input,15, stdin); 

    Family *newFamMember = malloc(sizeof(Family)); //create new address for newFamMember
    sscanf(input, "%s %d", newFamMember->name, &newFamMember->age); //takes the input (first a string then a integer) and stores it into its proper place

    printf("Added:%s Age:%d POINTING to:%S \n\n",newFamMember->name,newFamMember->age, newFamMember->next->name);

    newFamMember->next = NULL; //initialize it's pointer member var but more importantly maintains the linked list by pointing to null.

    /*Now we tell the computer what to do if this isn't the first node
    or not. If it is then there isn't a previous node so there is no
    way to set any other nodes' pointers to point to something else*/
    if ( previous != NULL){
        previous->next = newFamMember; //if previous is not equal to NULL set the previous' next pointer to newFamMember
        printf("previous:%s ", previous->next->name);
    }

    return newFamMember; //we always want to return a newly added family member. That's this function's purpose
}

/*now we can print the list*/
void PrintList (Family *head) { //start is a pointer so we can pass the value of start

    Family *currentMember = head; //we create currentMember and set it equal to start so we can iterate through the list and print each one

    int count = 0;
    if (currentMember == NULL){
        printf("There are no family members\n");
    }

    while (currentMember != NULL) {
        count++;
        printf("\n\nmember:%d Name:%s Age:%2d POINTING TO:%s\n",
                        count, currentMember->name, 
                        currentMember->age, 
                        currentMember->next->name);
        currentMember = currentMember->next; //move to the next node in the list headed towards NULL
    }
}

void CleanUp(Family *head){
    Family *freeMe = head;
    Family *holdMe = NULL;  
    while(freeMe != NULL) {
        holdMe = freeMe->next;
        printf("\nFree Name:%s Age:%d\n",
            freeMe->name,
            freeMe->age);
        free(freeMe);
        freeMe = holdMe;
        //PrintList(*start);
    }   
}

---

在“添加”部分，如果（head==NULL），则很可能是

，即比较而不是赋值。不幸的是，这不会改变任何事情。我也试过了@Moehm真的@Moehm？您更改了PrintList函数中的if（head==NULL）？Notepad++只是文本编辑器。警告来自编译器；它不会给你警告。您正在使用编译器进行编译；这应该给你一些警告。了解如何打开它们，然后打开它们并注意警告。将警告视为错误-C编译器比您在现阶段更了解C。