不知道如何使用这些作为原型给出的未命名结构。 C

Question

EDIT: These structure definitions were given to me and cannot be altered in any way.

Let's say in struct DB I would like to access the name of 3rd element in db. How would I go about that? I would think I would be able to do this:

DB->db[2].name;

but that doesn't work.

Also, how would I define one of these structs as a parameter inside a function?

typedef struct {
    char name[MAX_NAME + 1];
    unsigned long pass;
} DBEntry;

typedef struct {
    DBEntry db[MAX_ENTRIES];
    int size;
} DB;

Answer 1

First you have to create object for struct DB . Then you can access it's members.

DB obj;
strcpy(obj.db[2].name, "abc");

Answer 2

These are types , not variables .

To use them:

DB db;
db.size = 1;
strcpy(db.db[0].name, "name");
db.db[0].pass = 0xdeadbeef;
...

Answer 3

First of all, there is no struct DB ; there is a type name DB which identifies an untagged structure type, but that's separate from struct DB .

How you access the elements depends on the variable declaration:

DB  db1 = ...;
DB *db2 = ...;

With variable db1 , you access the name of the 3rd element using:

printf("%s\n", db1.db[2].name);

With variable db2 , you access the name of the 3rd element using:

printf("%s\n", db2->db[2].name);

You can define a function that takes these types using:

void magic_function(DB db1, DB *db2, DBEntry de1, DBEntry *de2)
{
    printf("%s\n", db1.db[0].name);
    printf("%s\n", db2->db[0].name);
    printf("%s\n", de1.name);
    printf("%s\n", de2->name);
}

You can declare it in a header using:

extern void magic_function(DB db1, DB *db2, DBEntry de1, DBEntry *de2);

Personally, I prefer the extern there for symmetry with the extern declarations for those rare global variables that are declared in the same header, but it is not actually necessary ( extern is assumed if it is omitted). If the function is only referenced from a single source file, it should be static , of course (and not declared in any header).

Answer 4

First you have to declare as object like this ..

DB db1;
db1.db[0].pass = 35;

I think , In your code , you have try to store number of names and access to those elements. If you try that, your DBEntry structure should be

typedef struct {
    char *name[MAX_NAME + 1];
    unsigned long pass;
} DBEntry;