与使用结构对C分配内存错误 [英] Allocation memory error with use struct for c
问题描述
我写了一个code管理库;编译完成，但在仿真过程中我获得了分配错误（情形2），我不知道为什么。
第一种情况下正常工作，但如果我在第一种情况中输入多个名称，第二种情况下不能正常工作。
我做了什么错？我希望我是很清晰。
typedef结构{
焦炭名[80];
焦炭**书籍;
INT books_num;
}认购;诠释主（）{
//变量声明：
INT选项= 0，subs_num = 0，I = 0，books_num = 0;
认购* subs_library;
焦炭**书籍;
炭subs_new_name [80]，book_new_name [80]; 的printf（请选择一个选项\\ n）;
做{
scanf函数（％d个，＆安培;可选）;
开关（选配件）{
情况1：
的printf（案例1：输入新的名称\\ n）;
scanf函数（％S，subs_new_name）;
如果（subs_num == 0）{
subs_library =的malloc（sizeof的（认购））;
}其他{
subs_library =的realloc（subs_library，sizeof的（认购））;
}
的strcpy（subs_library [subs_num] .name和subs_new_name）;
subs_library [subs_num] .books_num = 0;
subs_num ++;
的printf（添加\\ n）;
打破; 案例2：
的printf（案例2：输入书名\\ n）;
scanf函数（％S，book_new_name）; 如果（books_num == 0）{
书=的malloc（sizeof的（字符*））;
书[books_num] =的malloc（80 * sizeof的（炭））;
}其他{
书= realloc的（书，的sizeof（字符*））;
书[books_num] =的malloc（80 * sizeof的（炭））;
} 如果（书[books_num] == NULL）{
的printf（分配错误。\\ n）;
出口（1）;
} 的strcpy（书[books_num]，book_new_name）;
books_num ++;
的printf（添加\\ n）;
打破;
}
}而（选项= 7！）;
返回0;
}
您code重新分配数组是不正确。你没有分配足够的空间用于新数组的大小。当您重新分配这些数组，你通过一个单一的元素的大小，所以数组仍然有1而不是的长度subs_num + 1 。传递给的realloc 的大小应该是元素的倍大小以字节为单位的单个元素的。数
初始化 subs_library 和图书到 NULL 和变革阵列重新分配：
如果（subs_num == 0）{
subs_library =的malloc（sizeof的（认购））;
}其他{
subs_library =的realloc（subs_library，sizeof的（认购））;
}
进入这个：
subs_library = realloc的（subs_library，（subs_num + 1）* sizeof的（* subs_library））;
和对书做同样的，更改：
如果（books_num == 0）{
书=的malloc（sizeof的（字符*））;
书[books_num] =的malloc（80 * sizeof的（炭））;
}其他{
书= realloc的（书，的sizeof（字符*））;
书[books_num] =的malloc（80 * sizeof的（炭））;
}
要这样：
书籍= realloc的（书，（books_num + 1）* sizeof的（*书））;
书[books_num] =的malloc（80 * sizeof的（炭））;
或者更简单的：
书籍= realloc的（书，（books_num + 1）* sizeof的（*书））;
书[books_num] =的strdup（book_new_name）;
I wrote a code for managing a library; the compilation is done but during the simulation I obtained an Allocation error (case2) and I don't know why.
The first case works correctly but if I entered more than one name in the first case, the second case doesn't work.
What did I do wrong? I hope I was clear enough.
typedef struct {
char name[80];
char **books;
int books_num;
} Subscription;
int main() {
// Variables declaration:
int option = 0, subs_num = 0, i = 0, books_num = 0;
Subscription *subs_library;
char **books;
char subs_new_name[80], book_new_name[80];
printf("Choose an option\n");
do {
scanf("%d", &option);
switch (option) {
case 1:
printf("Case 1: enter a new name\n");
scanf("%s", subs_new_name);
if (subs_num == 0) {
subs_library = malloc(sizeof(Subscription));
} else {
subs_library = realloc(subs_library, sizeof(Subscription));
}
strcpy(subs_library[subs_num].name, subs_new_name);
subs_library[subs_num].books_num = 0;
subs_num++;
printf("ADDED\n");
break;
case 2:
printf("Case 2: enter the book name\n");
scanf("%s", book_new_name);
if (books_num == 0) {
books = malloc(sizeof(char*));
books[books_num] = malloc(80 * sizeof(char));
} else {
books = realloc(books, sizeof(char*));
books[books_num] = malloc(80 * sizeof(char));
}
if (books[books_num] == NULL) {
printf("Allocation Error\n");
exit(1);
}
strcpy(books[books_num], book_new_name);
books_num++;
printf("ADDED\n");
break;
}
} while (option != 7);
return 0;
}
Your code to reallocate the arrays is incorrect. You do not allocate enough room for the new array sizes. When you reallocate these arrays, you pass the size of a single element, therefore the array still has a length of 1 instead of subs_num + 1. The size passed to realloc should be the number of elements times the size of a single element in bytes.
Initialize subs_library and books to NULL and change your array reallocations:
if (subs_num == 0) {
subs_library = malloc(sizeof(Subscription));
} else {
subs_library = realloc(subs_library, sizeof(Subscription));
}
Into this:
subs_library = realloc(subs_library, (subs_num + 1) * sizeof(*subs_library));
And do the same for books, change:
if (books_num == 0) {
books = malloc(sizeof(char*));
books[books_num] = malloc(80 * sizeof(char));
} else {
books = realloc(books, sizeof(char*));
books[books_num] = malloc(80 * sizeof(char));
}
To this:
books = realloc(books, (books_num + 1) * sizeof(*books));
books[books_num] = malloc(80 * sizeof(char));
Or simpler:
books = realloc(books, (books_num + 1) * sizeof(*books));
books[books_num] = strdup(book_new_name);
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