c - 关于结构体的动态分配数组并在函数之间发送它

Question

我有一些问题，我想知道我做错了什么，是否有人可以向我解释有关 realloc 和 malloc 函数的更多详细信息。我遇到的问题来 self 的主要问题:

typedef struct Books {
   char *id;
   char *title;
   char *author;
   char *pages;
   char *year;
   char *subject;
} book;
char* filename;
int bookcount=1;
int libsize=4;
int main(int argc, char* argv[]){
 if (argc < 2)
    return -1;
 filename=argv[1];
 FILE* fptr;
 book* books;
 char tempstring[maxsize],* token;
 int i=0,ch;
 fptr=fopen(filename,"r");
 if(fptr==NULL)
    return-1;
//this count how many books are in the file
  while(ch!= EOF){
    ch=fgetc(fptr);
    if(ch == '\n')
    ++bookcount;
  }
 fclose(fptr);
 while(libsize<bookcount){
    libsize *= 1.5;
 }
 books=(book*) malloc(libsize*sizeof(book));
 if(books==NULL)
    exit(-1);

 fptr=fopen(filename,"r");
 if(fptr==NULL)
    return-1;
//this gets all the books into the book array
  for(i=0;i<bookcount;i++){
    fgets(tempstring,maxsize,fptr);
    token=strtok(tempstring,",");
    ch=strlen(token);
    books[i].id=(char*)malloc(ch+1);
    strcpy(books[i].id,token);
    token=strtok(NULL,",");
    ch=strlen(token);
    books[i].title=(char*)malloc(ch+1);
    strcpy(books[i].title,token);
    token=strtok(NULL,",");
    ch=strlen(token);
    books[i].author=(char*)malloc(ch+1);
    strcpy(books[i].author,token);
    token=strtok(NULL,",");
    ch=strlen(token);
    books[i].pages=(char*)malloc(ch+1);
    strcpy(books[i].pages,token);
    token=strtok(NULL,",");
    ch=strlen(token);
    books[i].year=(char*)malloc(ch+1);
    strcpy(books[i].year,token);
    token=strtok(NULL,",");
    ch=strlen(token);
    books[i].subject=(char*)malloc(ch+1);
    strcpy(books[i].subject,token);
   }
  books=(book*) realloc(books,libsize*sizeof(book));
  fclose(fptr);
    printf("to add a book press 1\n");
    printf("to delete a book press 2\n");
    printf("to find a book press 3\n");
    printf("to print all books press 4\n");
    printf("to save library in a file press 5\n");
    printf("to add books from a file press 6\n");
    printf("to exit press 0\n");
    pick(books);
    free(books);
    return 1;
}

我将动态分配的结构数组发送到一个函数中，让我选择现在当我打电话打印书籍时

void printbooks(book* books){
    int i;
    for(i=0;i<bookcount;++i){
        printf("%s\n",books[i].title);
    }
    printf("Fin\n");
    pick(books);
}

我得到了预期的输出当我使用 addbook 函数时如何

void addbook(book* books){
    char tempstring[maxsize];
    gets(tempstring);
    book* temp;
    int i=bookcount-1,ch;
    ++bookcount;
    if(libsize < bookcount){
    while(libsize < bookcount){
    libsize*=1.5;}
    temp=(book*)realloc(books,libsize);
    }
    if(temp==NULL){
        printf("no more space\n");
        exit(-1);}

    if(temp!=NULL){
        books=temp;}

    printf("add the id\n");
    gets(tempstring);
    ch=strlen(tempstring);
    books[i].id=(char*)malloc(ch+2);
    strcpy(books[i].id,tempstring);
    printf("add the title\n");
    gets(tempstring);
    ch=strlen(tempstring);
    books[i].title=(char*)malloc(ch+2);
    strcpy(books[i].title,tempstring);
    printf("add the author\n");
    ch=strlen(tempstring);
    books[i].author=(char*)malloc(ch+2);
    gets(tempstring);
    strcpy(books[i].author,tempstring);
    printf("add the pages\n");
    gets(tempstring);
    ch=strlen(tempstring);
    books[i].pages=(char*)malloc(ch+2);
    strcpy(books[i].pages,tempstring);
    printf("add the year\n");
    gets(tempstring);
    ch=strlen(tempstring);
    books[i].year=(char*)malloc(ch+2);
    strcpy(books[i].year,tempstring);
    printf("add the subject\n");
    gets(tempstring);
    ch=strlen(tempstring);
    books[i].subject=(char*)malloc(ch+2);
    strcpy(books[i].subject,tempstring);

    printf("book number %d added",bookcount);
    printf("\n");
    pick(books);
}

一些结构成员被损坏，程序崩溃，当我尝试将库大小更改为 20，然后在我尝试输入新书的第一个成员时运行它时，程序崩溃了。

Answer 1

在addbook

void addbook(book* books){
    ..
    libsize*=1.5;}
    temp=(book*)realloc(books,libsize);
    }

realloc 调用未正确调整数组大小(您可以在另一个函数中正确执行此操作)。它应该包括字体大小:

temp = realloc(books,libsize*sizeof(book));

否则它会缩小大小，并且您会出现损坏/未定义的行为，因为例如内存会在其他地方重用。

一般注意事项:这些分配函数很棘手且容易出错:最好将它们放在实用函数中并且仅使用函数，不要复制/粘贴此类代码一百万次(例如: malloc(ch+2) 分配 1 个字节太多，很多次)。对于您的代码，可以使用审查。