Incorrectly storing Ints?

silentwizardlord@hotmail. · *nix forums beginner Joined: 08 Feb 2005 Posts: 2

Thank you Michael for your very prompt, and accurate reply.

I tested the code:

player p;
memcpy(&p, data.get_data(), sizeof(player));
int money = p.money;

And it worked perfectly. I knew it was something simple.

Once again, thank you

Micah

Michael Cahill · *nix forums Guru Wannabe Joined: 26 May 2005 Posts: 219

Hi Micah,

I'm not exactly sure what's causing your problem, but here are a few
things to check. When you do the put:

ret = db2.put(0,&key2,&data2,DB_NOOVERWRITE);

are you sure that ret == 0? You didn't show that code. If the key
already exists with different data, you'd get DB_KEYEXIST and the
database would be unchanged.

When you do the get:

player *pmon;
pmon = (player *)data.get_data();
int money = pmon->money;

You are making an assumption that the data in the Dbt is aligned. In
other words, you are assuming that it is okay to cast it to a pointer
of a different type, which may not be valid in this case. Instead, try
this:

player p;
memcpy(&p, data.get_data(), sizeof(player));
int money = p.money;

You can avoid copying the data using the DB_DBT_USERMEM flag on the
data Dbt passed in to the Db::get call.

I hope this helps.

Michael.

silentwizardlord@hotmail. · *nix forums beginner Joined: 08 Feb 2005 Posts: 2

Hello,

I want to start out by saying I've spent the better half of today
googling for any information I could find. I've spent most of this
night searching this group for any information. So I have researched
this some.

Here is my problem. I have no problem storing and recalling char
pointers. But every attempt to store and retrieve an int has failed.
Well, not so much failed as returned the wrong int. I feed my code an
int with the value of 10000, and I get an int with the value of
21474952, a slight difference.

Here is some of the code.

//BEGINING OF CODE
class player{
public:
int money;
};
....
player newplayer;
newplayer.money = 10000;
std::cout << "IN: MONEY: " << newplayer.money << std::endl; // IN:
MONEY: 10000
....
Db db2(0, 0);
db2.set_error_stream(&std::cerr);
db2.set_errpfx("sm.h");
db2.set_pagesize(1024);
db2.set_cachesize(0, 32 * 1024, 0);
Dbt key2("cppclass",(strlen("cppclass") + 1));
Dbt data2(&newplayer,sizeof(newplayer));
db2.open(NULL,tmppath.c_str(),"maininfo", DB_BTREE, DB_CREATE, 0664);
try {
ret = db2.put(0,&key2,&data2,DB_NOOVERWRITE);
}
catch (DbException &dbe) {
std::cerr << "sm.h: " << dbe.what() << "\n";
}
db2.close(0);
....
Db db(0, 0);
db.set_error_stream(&std::cerr);
db.set_errpfx("sm.h");
db.set_pagesize(1024);
db.set_cachesize(0, 32 * 1024, 0);
Dbt key((char *)"cppclass", (strlen("cppclass") + 1));
Dbt data;
db.open(NULL, tmppath.c_str(),"maininfo", DB_BTREE, DB_CREATE, 0664);
try {
db.get(NULL,&key, &data, 0);
}
catch (DbException &dbe) {
std::cerr << "sm.h: " << dbe.what() << "\n";
}
db.close(0);
player *pmon;
pmon = (player *)data.get_data();
int money = pmon->money;
std::cout << "OUT: Money: " << money << std::endl; // OUT: Money:
21474952
//END OF CODE

I'm on Win32(XP) using MinGW32, BerkeleyDB 4.3 (locally built with
MinGW) I'm sure it is just a problem with my coding, but I cannot find
a single helpful tutorial, example, FAQ, forum, or anything that solves
my problem.

Also, the program compiles and links just fine, I'm just not getting
the value I tell it.

Thanks in advance.

Micah

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