错误：预期'：'，'，'，';'，'}'或'__attribute__'

Question

我正在创建一个以链表的形式在内存中加载文件的函数。但是当我编译代码时，错误就出现了：error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’

代码在

之下

load_file.c：

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

struct node{
    char* data = NULL;
    struct node* next = NULL;
};

struct node* head = NULL;
struct node* tail = NULL;

int load_file(char* file_name){

    char line[1000];
    char* data = NULL;
    struct node* temp = NULL;

    FILE* fp = fopen(file_name,"r");

    if(fp == NULL){
        printf("cannot open the file\n");
        return -1;
    }
    while(fscanf(fp,"%99s",line) == 1){
        data = (char*)malloc(sizeof(char) * strlen(line));
        if(data == NULL){
            printf("could not allocate memory for string\n");
            return -2;
        }

        strcpy(data,line);

        temp = (struct node*)malloc(sizeof(struct node));
        if(temp == NULL){
            printf("could not allocate memory for node\n");
        }
        if(head == NULL){
            head = temp;
            tail = temp;
        }else{
            tail->next = temp;
            tail = tail->next;
        }
    }

    return 0;
}

load_file.h：

int load_file(char*);

test.c的：

#include<stdio.h>
#include"load_file.h"

int main(){

    char* file= "text.txt";

    printf("ruuning\n");
    load_file(file);
    printf("done");


    return 0;
}

编译错误时：

harsh@harsh-Inspiron-3558:~/c/bank_management/include/load_file$ sudo gcc test.c load_file.c -o test
load_file.c:6:13: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘=’ token
  char* data = NULL;
             ^
load_file.c: In function ‘load_file’:
load_file.c:42:8: error: ‘struct node’ has no member named ‘next’
    tail->next = temp;
        ^
load_file.c:43:15: error: ‘struct node’ has no member named ‘next’
    tail = tail->next;
               ^

对于任何错误抱歉。我是初学者。

Answer 1

C结构没有成员的默认值。从结构定义中删除= NULL。如果您希望最初将值清零，请使用calloc而不是malloc分配结构，或者如果它是堆栈或全局变量（不是堆分配），则将其声明/初始化为{{1 }}

Answer 2

您不会在类型定义中添加初始值设定项;变化

struct node{
    char* data = NULL;
    struct node* next = NULL;
};

到

struct node{
  char *data;
  struct node *next;
};

您在创建struct node的实例时初始化这些字段，如下所示：

struct node foo = {NULL, NULL};

或

struct node foo = { .data = NULL, .next = NULL }; // as of C99

或

struct node foo;
...
foo.data = NULL;
foo.next = NULL;

或

struct node foo;
...
foo = (struct node){.data = NULL, .next = NULL}; // as of C99

或

struct node *foo = malloc( sizeof *foo );
foo->data = NULL;
foo->next = NULL;

或

struct node *foo = malloc( sizeof *foo );
*foo = (struct node){.data = NULL, .next = NULL}; // as of C99

请注意，

时

struct node *foo = calloc( 1, sizeof *foo );

会将*foo的字段初始化为所有位0，这与将它们初始化为NULL不一定相同 - 所有保证的是零值常量表达式等同于NULL，而不是零值运行时表达式。