警告：使用 gcc -std=c89 -g –pedantic filename.c 编译时从不兼容的指针类型赋值

Question

我正在使用链表实现队列。需要使用命令 gcc -std=c89 -g –pedantic filename.c 在 omega 上编译代码而不发出警告。但是，我收到警告：行号（174、223、253）上的不兼容指针类型赋值 [默认启用]。另外，我在将记录打印到文件时遇到问题：

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

struct student_record
{
        int student_id_;
        int student_age_;
        char first_name_[21];
        char last_name_[21];
};

struct student_record_node
{
        struct student_record* record_;
        struct student_record_node* next_;
}*front,*rear,*temp,*front1;

void enq(struct student_record* sr);
void parseFile(char* filename, struct student_record_node** head);
void printNode(struct student_record_node* node);
struct student_record_node* student_record_allocate();
void student_record_node_deallocate(struct student_record_node* node);
void sortByAge(struct student_record_node** recordsHead);
void sortById(struct student_record_node** front);
void swap(struct student_record_node** node1, struct student_record_node** node2);

int main ( int argc, char *argv[] )
{
        char *filename = argv[1];
        int i;

     /**for(i=0;i<argc;i++)**/
    /**         printf("%d %s ",i,argv[i]);**/


   /**printf( "usage: %s filename", argv[1] );**/
    parseFile(filename,&front);
    printNode(front);

    printf("\n");
    printf("Sorting by age \n");
    sortByAge(&front);
    printNode(front);

    printf("Sorting by id \n");
    sortById(&front);
    printNode(front);

    /**student_record_node_deallocate(front);**/
    getch();
    return 0;
}

void swap(struct student_record_node** node1, struct student_record_node** node2)
{
     struct student_record *s1;
     struct student_record_node *t1 = *node1,*t2=*node2;

     /**s1=(struct node *)malloc(1*sizeof(struct student_record));**/

     s1= t1 -> record_;

     t1->record_= t2->record_;
     t2->record_=s1;

}

void sortByAge(struct student_record_node** front)
{
    int swapped, i;
    struct student_record_node *ptr1;
    struct student_record_node *lptr = NULL;
    struct student_record *s1,*s2;

    /**Checking for empty list**/
    if (ptr1 == NULL)
        return;

    do
    {
        swapped = 0;
        ptr1 = *front;

        while (ptr1->next_ != lptr)
        {
            s1=ptr1->record_;
            s2=ptr1->next_->record_;
            if (s1->student_age_ > s2->student_age_)
            {
                swap(&ptr1, &ptr1->next_);
                swapped = 1;
            }
            ptr1 = ptr1->next_;
        }
        lptr = ptr1;
    }
    while (swapped);



}

void sortById(struct student_record_node** front)
{
    int swapped, i;
    struct student_record_node *ptr1;
    struct student_record_node *lptr = NULL;
    struct student_record *s1,*s2;

    /**Checking for empty list**/
    if (ptr1 == NULL)
        return;

    do
    {
        swapped = 0;
        ptr1 = *front;

        while (ptr1->next_ != lptr)
        {
            s1=ptr1->record_;
            s2=ptr1->next_->record_;
            if (s1->student_id_ > s2->student_id_)
            {
                swap(&ptr1, &ptr1->next_);
                swapped = 1;
            }
            ptr1 = ptr1->next_;
        }
        lptr = ptr1;
    }
    while (swapped);



}



void student_record_node_deallocate(struct student_record_node* node)
{
    front1 = node;
    struct student_record_node* temp;


    if ((front1 == NULL) && (rear == NULL))
    {
        printf("Queue is empty");
        return;
    }
    while (front1 != rear)
    {
        temp =front1;
        front1 = front1->next_;
        free(temp);

    }
    if (front1 == rear)
        {
         free(front1);
        }

    free(node);
    free(temp);

}

struct student_record_node* student_record_allocate()
{
 struct student_record_node* sr;
 sr = (struct node *)malloc(1*sizeof(struct student_record_node));
 return sr;

}

void printNode(struct student_record_node* node)
{
    front1 = front;
    struct student_record* s;


    if ((front1 == NULL) && (rear == NULL))
    {
        printf("Queue is empty");
        return;
    }
    while (front1 != rear)
    {
        s=front1->record_;
         printf("struct student_record_node\n");
         printf("\tstudent firstname %s\n", s->first_name_);
         printf("\tstudent lastname %s\n", s->last_name_);
         printf("\tstudent id %d\n", s->student_id_);
         printf("\tstudent age %d\n\n", s->student_age_);
        front1 = front1->next_;
    }
    if (front1 == rear)
        {
         s=front1->record_;
         printf("struct student_record_node\n");
         printf("\tstudent firstname %s\n", s->first_name_);
         printf("\tstudent lastname %s\n", s->last_name_);
         printf("\tstudent id %d\n", s->student_id_);
         printf("\tstudent age %d\n\n", s->student_age_);
        }
}

void enq(struct student_record* sr)
{

    if (rear == NULL)
    {
        rear = student_record_allocate();//(struct node *)malloc(1*sizeof(struct student_record_node));
        rear->record_ = sr;
        rear->next_ = NULL;
        front = rear;
    }
    else
    {
        temp=(struct node *)malloc(1*sizeof(struct student_record_node));
        rear->next_ = temp;
        temp->record_ = sr;
        temp->next_ = NULL;

        rear = temp;
    }

}
void parseFile(char* filename, struct student_record_node** head)
{
  struct student_record * sr;


  char item[21], status[21];
  int id,age;


  FILE *fp;

  if((fp = fopen(filename, "r+")) == NULL) {
        printf("No such file\n");
        exit(1);
    }

    while (true) {
        int ret = fscanf(fp, "%s %s %d %d", item, status, &id, &age);
        if(ret == 4)
            {
                 /**printf("\n%s \t %s %d %d", item, status, id, age);**/
                  sr = (struct node *)malloc(1*sizeof(struct student_record));
                  strncpy(sr->first_name_, item, 21);
                  /**sr->first_name_ = item;**/
                  strncpy(sr->last_name_,status,21);
                  /**sr->last_name_ = status;**/
                  sr->student_id_=id;
                  sr->student_age_=age;
                  enq(sr);
            }
        else if(errno != 0) {
            perror("scanf:");
            break;
        } else if(ret == EOF) {
            break;
        } else {
            printf("No match.\n");
        }
    }
    printf("\n");
    /*if(feof(fp)) {
        puts("EOF");
    }*/
}

输入文件是：

Joe Smith 00001 24
Bob Smith 00002 31
Samantha Smith 00003 30
Christina Smith 00004 17
Steven Smith 00005 20
Jason Smith 00006 3
Patrick Smith 00007 50
Alex Smith    00001 29

Answer 1

你永远不应该使用 malloc 的 return。 See this link as to why should not.

所以，更改第 174 行的代码。

sr = (struct node *)malloc(1*sizeof(struct student_record_node));

到

sr = malloc(1*sizeof(struct student_record_node));

对所有三个重复此操作 lines.Other 然后排序似乎没问题。

要打印到文件，您可以使用函数 fprintf(fp,"....") 而不是使用 printf

Answer 2

它是 (mmm...) 因为您正在分配一个不兼容的指针类型。

struct student_record_node* sr;
sr = (struct node *)malloc(1*sizeof(struct student_record_node));

在这里，您将 malloc 的 return 值转换为 "pointer to struct node"，然后将其分配给 "pointer to struct student_record_node."

其实演员阵容很烂。扔掉它。 malloc的return值为void*，与任何其他指针兼容。此外，您可以使用位置作为 sizeof 的参数，这有很多好处。 1* 只是混乱。所以你剩下：

struct student_record_node *sr = malloc(sizeof *sr);

错误将消失。

然后检查 NULL return 值。就算是玩具，也要早点养成真正程序员的习惯。

此外，学习 c89 语法也不是最好的主意，尤其是作为新程序员。在非平凡的情况下，它实际上需要糟糕的风格。为什么你认为 gcc 需要一个标志来强制它？我知道这可能超出了你的控制范围，但我会向老师提出。

"Facing problems" 不是问题。如果您需要特定的帮助，通常可以在这里找到。

Answer 3

检查这一行

if (ptr1 == NULL)
    return;

应该是 "front" 代替 "ptr"

警告：使用 gcc -std=c89 -g –pedantic filename.c 编译时从不兼容的指针类型赋值

warning: assignment from incompatible pointer type when compiling using gcc -std=c89 -g –pedantic filename.c

c

pointers

c89