[英]C Dynamically allocated a struct in an array that is inside another struct
所以為了很好地總結一下,我有一個主要的結構,它是一個目錄,它包含一個計數器(它擁有的書籍)、容量(它可以支持的書籍總數,也可以增長)和一個數組指向另一個包含書籍信息的結構的指針。
typedef struct BooksInStock{
int id;
char title[MAX_TITLE]; // 38 Characters
char author[MAX_AUTHOR]; // 20 Characters
double level;
int words;
}Books;
typedef struct Stock {
Books *b;
int count;
int capacity;
} Stock;
確切的 valgrind 錯誤是:
==23844== Invalid read of size 4
==23844== at 0x401418: idComp (catalog.c:27)
==23844== by 0x4E6FC62: msort_with_tmp.part.0 (in /usr/lib64/libc-2.17.so)
==23844== by 0x4E6FBD7: msort_with_tmp.part.0 (in /usr/lib64/libc-2.17.so)
==23844== by 0x4E6FFB6: qsort_r (in /usr/lib64/libc-2.17.so)
==23844== by 0x401AE3: listAll (catalog.c:168)
==23844== by 0x400C13: main (reading.c:73)
==23844== Address 0x6e61724674666172 is not stack'd, malloc'd or (recently) free'd
我假設這是因為我沒有正確分配我的結構/數組,但我之前不必在另一個結構中動態分配一個結構數組,我相信我自己很困惑。
編輯:我分配了錯誤的內存,請參閱: C 用 printf 打印非常奇怪的值
編輯:正如所指出的,我忘記了調用 idComp 的方法
void listAll(Catalog *cat)
{ // cat is just the catalog of books that have been read in already
qsort(cat->b, cat->count, sizeof( Books ), idComp); // idComp is called here
if (cat->count == 0) {
printf("No matching books");
} else {
printf("%5s %38s %20s %5s %7s", "ID", "Title", "Author", "Level", "Words");
for (int i = 0; i < cat->count; i++) {
printf("%5d %38s %20s %5.1f %7d", cat->b[i].id, cat->b[i].title,
cat->b[i].author, cat->b[i].level, cat->b[i].words);
}
}
printf("\n");
}
cat->b
點的數組Books
,傳遞給的比較函數,那么什么qsort
是指向Books
,而不是指針的指針,以Books
。
因此, idComp
函數應該是這樣的:
static int idComp( const void *aptr, const void *bptr )
{
const Books *a = aptr;
const Books *b = bptr;
if ( a->id < b->id )
return -1;
if ( a->id > b->id )
return 1;
return 0;
}
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