C语言: structs and character arrays

Question

当我尝试 printf() 数据的值时，我什么也得不到，但如果我这样做 date = "text" 它就会起作用。有谁知道原因吗？

struct aac { char **data; };

int main ( ) {
    char* value = malloc ( 100 );
    strcpy ( value, "test" );
    struct aac b;  
    b.data = malloc ( 100 );  
    cake ( value, &b );  
    donut ( &b );
    return 0;  
}

int cake ( char *value, struct aac *c ) {  
    c->data[0] = value;  
    return 0;  
}

int donut ( struct aac *b ) {  
    printf ( "%s", b->data[0] );
    return 0;
}

Answer 1

也许这个例子可能有帮助:

#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <errno.h>

struct aac {
   char **pastries;
};

void
init_pastries (struct aac * rec_p, int max)
{
  /* Allocate space for max #/pastries, plus a NULL delimiter */
  int nbytes = sizeof (char *) * (max+1);
  rec_p->pastries = (char **)malloc (nbytes);
  memset (rec_p->pastries, 0, nbytes);
  printf ("init_pastries: max #/pastries: %d, malloc: %d bytes...\n",
    max, nbytes);
}

void
add_pastry (char * name, int i, struct aac *rec_p)
{
  int nbytes = strlen (name) + 1;
  rec_p->pastries[i] = (char *)malloc (nbytes);
  strcpy (rec_p->pastries[i], name);
  printf ("add_pastry (%s): malloc= %d bytes...\n",
    name, nbytes);
}

void
print_pastries (struct aac * rec_p)
{
  char **s = NULL;
  for (s = rec_p->pastries; (*s); s++)
    printf ("pastry: %s...\n", *s);
}

int
main ( ) {
    struct aac rec;
    init_pastries (&rec, 5);
    add_pastry ("cake", 0, &rec);
    add_pastry ("donut", 1, &rec);
    print_pastries (&rec);
    return 0;
}

这是示例输出:

gcc -o tmp tmp.c

./tmp 
  init_pastries: max #/pastries: 5, malloc: 24 bytes... add_pastry
  (cake): malloc= 5 bytes... add_pastry
  (donut): malloc= 6 bytes... pastry:
  cake... pastry: donut...

“希望有帮助......至少有一点:)