Hi, all.

I want to know the scope od datafield of DBT struct.

When i get one record, the data struct has valid data region pointer.
but how can I assure a validity of that pointer?

when I return that pointer, is valid that data region in memory?

Thanks in advance.

BYTE* ReturnAsPointer()
{
DBT key, data;
....................
return data.data;

}
void TestFunc()
{
BYTE * pReturnData = ReturnAsPointer();

}


In TestFunc, is the pReturnData valid?
if not valid, should i must allocating heap memory and copy to there?



NightThunder 작성:

Hi NightThunder,

Please note that all fields of the DBT structure that are not
explicitly set should be initialized to null bytes before the first
time the structure is used.
In your case, the code would look like this in the ReturnAsPointer
function:

BYTE* ReturnAsPointer()
{
DBT key,data;
char* desc = "Content of the data field for the data DBT";
.................
/* Set to 0 the fields of the DBTs */
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
.................
data.data = desc;
data.size = (u_int32_t) strlen(desc) + 1;
................
return (BYTE*) data.data;
}

In the TestFunc function the pReturnData pointer can't be used to
modify the content of the data.data location. But still you can use it,
let's say to display the content of data.data. In order to use a valid
pointer you should allocate heap memory like:

BYTE* pReturnData = ReturnAsPointer();
u_int32_t strSize = (u_int32_t) strlen(pReturnData) + 1;

BYTE* pTestData = (BYTE*) malloc(strSize);

A test function for you could be:

void TestFunc()
{
BYTE* pReturnData = ReturnAsPointer();
u_int32_t strSize = (u_int32_t) strlen(pReturnData) + 1;

BYTE* pTestData = (BYTE*) malloc(strSize);

cout<<"\n Data field of the data DBT is: "<<pReturnData;
cout<<"\n Size of data field of the data DBT is: "<<strSize<<"\n";
..............................
}

Regards,

Andrei Costache
Berkeley DB
Oracle Support Services