computer name length issue

[George2]

Hello everyone,

Any macro used to represent computer name max length (just host name max length itself, not full-qualified with domain suffix, for example, I just want host name "somehost" in example.com domain, but not "somehost.example.com")?

http://msdn.microsoft.com/en-us/libr...01(VS.85).aspx

MAX_COMPUTERNAME_LENGTH is too small and just 15 characters.

thanks in avdance,
George

[zerver]

I think it is 256, in which case you could use MAX_PATH.

[molotov]

GetComputerNameEx:

The length of the name may be greater than MAX_COMPUTERNAME_LENGTH characters because DNS allows longer names. To ensure that this buffer is large enough, set this parameter to NULL and use the required buffer size returned in the lpnSize parameter.

[George2]

Hi zerver,

I think it is 256, in which case you could use MAX_PATH.

Is there a built-in macro?

regards,
George

[George2]

Hi molotov, as mentioned in the MSDN document, if MAX_COMPUTERNAME_LENGTH macro is not suitable for DNS name, which macro should I use? Thanks.

GetComputerNameEx:

regards,
George

[molotov]

There is no macro.

lpBuffer
The length of the name may be greater than MAX_COMPUTERNAME_LENGTH characters because DNS allows longer names. To ensure that this buffer is large enough, set this parameter to NULL and use the required buffer size returned in the lpnSize parameter.

[cilu]

Hi molotov, as mentioned in the MSDN document, if MAX_COMPUTERNAME_LENGTH macro is not suitable for DNS name, which macro should I use? Thanks.



regards,
George

Many Windows API allow you to send a NULL buffer, and they return you the size required for the buffer. So you should use this technique, as molotov explained.

[George2]

Thanks molotov. There is macro.

#include <Windns.h>


//
//  DNS Names limited to 255, 63 in any one label
//
#define DNS_MAX_NAME_LENGTH             (255)
#define DNS_MAX_LABEL_LENGTH            (63)
#define DNS_MAX_NAME_BUFFER_LENGTH      (256)
#define DNS_MAX_LABEL_BUFFER_LENGTH     (64)

There is no macro.

regards,
George

[George2]

I have a better idea, cilu. Please refer to my post #8. :-)

Many Windows API allow you to send a NULL buffer, and they return you the size required for the buffer. So you should use this technique, as molotov explained.

regards,
George

[Paul McKenzie]

I have a better idea, cilu. Please refer to my post #8. :-)

Why is that a better idea? You still have no idea how long the actual name is, and macros aren't going to help you. Why not use the function as it was intended?

1) Call it once to return the length of the data.
2) Call it again, using the length returned from 1)

There are many Windows API functions that return a character buffer. How big that buffer can be is determined by calling the function with NULL or some other value that indicates "return the length to me, and not the data". Then you call the function a second time, now that you know the length of the data.

I'll even give you how to do this in C++ with any function that works this way:

#include <vector>
#include <windows.h>

void foo()
{
    DWORD length;

    // get the length first
    GetComputerNameEx( "whatever", NULL, &length );

    // create a buffer with the length
    std::vector<TCHAR> buffer(length + 1, 0);

    // now get the name
    GetComputerNameEx("whatever", &buffer[0], &length);
);

This way, you get the entire name, regardless if it is 1 character, 10, characters, or 10,000 characters.

Regards,

Paul McKenzie

[molotov]

Those constants are from the DNS API. They are not mentioned in the API doc for GetComputerNameEx. The documented method for "buffer sizing" with respect to this API has been discussed and illustrated.

[George2]

Thanks molotov,

The documented method for "buffer sizing" with respect to this API has been discussed and illustrated.

You mean the approach of calling it twice?

regards,
George

[George2]

Thanks Paul,

Why is that a better idea? You still have no idea how long the actual name is, and macros aren't going to help you. Why not use the function as it was intended?

1) Call it once to return the length of the data.
2) Call it again, using the length returned from 1)

There are many Windows API functions that return a character buffer. How big that buffer can be is determined by calling the function with NULL or some other value that indicates "return the length to me, and not the data". Then you call the function a second time, now that you know the length of the data.

I'll even give you how to do this in C++ with any function that works this way:

#include <vector>
#include <windows.h>

void foo()
{
    DWORD length;

    // get the length first
    GetComputerNameEx( "whatever", NULL, &length );

    // create a buffer with the length
    std::vector<TCHAR> buffer(length + 1, 0);

    // now get the name
    GetComputerNameEx("whatever", &buffer[0], &length);
);

This way, you get the entire name, regardless if it is 1 character, 10, characters, or 10,000 characters.

Regards,

Paul McKenzie

You are the man!

regards,
George

[cilu]

Thanks molotov,



You mean the approach of calling it twice?

regards,
George

Exactly.

[TheCPUWizard]

You mean the approach of calling it twice?

WHY are you still asking, is it was stated that this was the proper methodology all the way back in "Reply #3", back on December 16th!!!!!!