C / C++ / MFC

Re: can anybody help me in solving my problem with connecting to the database

8-Oct-07 0:59

are you able to execute queries?

Hamid_RT8-Oct-07 1:08

Re: can anybody help me in solving my problem with connecting to the database

8-Oct-07 1:08

I think this article is helpful for you.The CODBCDynamic class[^]

David Crow8-Oct-07 3:47

David Crow

8-Oct-07 3:47

philiptabraham wrote:
Can anybody tell me how to update /delete /insert into the table.

If you are using MFC, check out the CRecordset methods.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

union and struct

KASR17-Oct-07 23:47

7-Oct-07 23:47

In what way union differs from struct?

Maxwell Chen8-Oct-07 0:11

Maxwell Chen

8-Oct-07 0:11

Members of a union share the same address.

Maxwell Chen

Hamid_RT8-Oct-07 0:24

8-Oct-07 0:24

On the Union all members have same location on the memory so you can't store different values at the moment to other members.struct is similar to class however they have some differences.

KASR18-Oct-07 0:28

8-Oct-07 0:28

for example
union Sample
{
int a;
float b;
};

Sample D;

D.a = 10;
then
D.b = 20.0; will destroy D.a value. isn't it?

Hamid_RT8-Oct-07 0:45

8-Oct-07 0:45

Its better chechk this code

union abcd
{
	int a;
	int b;
};

struct abcd2
{
	int a;
	int b;
};

int _tmain(int argc, _TCHAR* argv[])
{
	abcd dd;
	dd.a=20;
	cout<<dd.a<<endl; -->output=20
	dd.b=110;	cout<<dd.b<<endl;  -->output=110
	cout<<dd.a<<endl;  --> output=110;

////////Structure////////////////
	abcd2 aa;
	aa.a=20;
	cout<<aa.a<<endl;  -->output=20;
	aa.b=110;
	cout<<aa.b<<endl;  -->output=110;
	cout<<aa.a<<endl;  -->output=20;

	return 0;
}

KASR18-Oct-07 0:55

8-Oct-07 0:55

Thanks to all.
Now it gives clear understanding.

lets continue the same discussion

Maxwell Chen8-Oct-07 0:34

Maxwell Chen

8-Oct-07 0:34

union A
{
	unsigned char cc[4];
	unsigned int nn;
};

void main()
{
	A obj;
	obj.nn = 0xabcd1234;
	printf("obj.cc[0]=0x%X, obj.cc[1]=0x%X, obj.cc[2]=0x%X, obj.cc[3]=0x%X\n",
		obj.cc[0],obj.cc[1],obj.cc[2],obj.cc[3]);

}

obj.cc[0]=0x34, obj.cc[1]=0x12, obj.cc[2]=0xCD, obj.cc[3]=0xAB
Press any key to continue . . .

Maxwell Chen

chandu0048-Oct-07 1:03

8-Oct-07 1:03

can any body explain some example like, where and in which contexts this can be applied?

Hamid_RT8-Oct-07 1:10

8-Oct-07 1:10

What do you need exactly?

chandu0048-Oct-07 1:14

8-Oct-07 1:14

some realtime example do demonstrate the use of union.

Hamid_RT8-Oct-07 1:22

8-Oct-07 1:22

For see some detaily of union I suggest see Other Data Types section on the www.cplusplus.com.;)

JudyL_MD8-Oct-07 2:27

JudyL_MD

8-Oct-07 2:27

chandu004 wrote:
some realtime example do demonstrate the use of union.

from wdm.h (a driver include file):

typedef struct _PCI_COMMON_HEADER {
    USHORT  VendorID;                   // (ro)
    USHORT  DeviceID;                   // (ro)
    USHORT  Command;                    // Device control
    USHORT  Status;
    UCHAR   RevisionID;                 // (ro)
    UCHAR   ProgIf;                     // (ro)
    UCHAR   SubClass;                   // (ro)
    UCHAR   BaseClass;                  // (ro)
    UCHAR   CacheLineSize;              // (ro+)
    UCHAR   LatencyTimer;               // (ro+)
    UCHAR   HeaderType;                 // (ro)
    UCHAR   BIST;                       // Built in self test

    union {
        struct _PCI_HEADER_TYPE_0 {
            ULONG   BaseAddresses[PCI_TYPE0_ADDRESSES];
            ULONG   CIS;
            USHORT  SubVendorID;
            USHORT  SubSystemID;
            ULONG   ROMBaseAddress;
            UCHAR   CapabilitiesPtr;
            UCHAR   Reserved1[3];
            ULONG   Reserved2;
            UCHAR   InterruptLine;      //
            UCHAR   InterruptPin;       // (ro)
            UCHAR   MinimumGrant;       // (ro)
            UCHAR   MaximumLatency;     // (ro)
        } type0;

        // PCI to PCI Bridge
        struct _PCI_HEADER_TYPE_1 {
            ULONG   BaseAddresses[PCI_TYPE1_ADDRESSES];
            UCHAR   PrimaryBus;
            UCHAR   SecondaryBus;
            UCHAR   SubordinateBus;
            UCHAR   SecondaryLatency;
            UCHAR   IOBase;
            UCHAR   IOLimit;
            USHORT  SecondaryStatus;
            USHORT  MemoryBase;
            USHORT  MemoryLimit;
            USHORT  PrefetchBase;
            USHORT  PrefetchLimit;
            ULONG   PrefetchBaseUpper32;
            ULONG   PrefetchLimitUpper32;
            USHORT  IOBaseUpper16;
            USHORT  IOLimitUpper16;
            UCHAR   CapabilitiesPtr;
            UCHAR   Reserved1[3];
            ULONG   ROMBaseAddress;
            UCHAR   InterruptLine;
            UCHAR   InterruptPin;
            USHORT  BridgeControl;
        } type1;

        // PCI to CARDBUS Bridge
        struct _PCI_HEADER_TYPE_2 {
            ULONG   SocketRegistersBaseAddress;
            UCHAR   CapabilitiesPtr;
            UCHAR   Reserved;
            USHORT  SecondaryStatus;
            UCHAR   PrimaryBus;
            UCHAR   SecondaryBus;
            UCHAR   SubordinateBus;
            UCHAR   SecondaryLatency;
            struct  {
                ULONG   Base;
                ULONG   Limit;
            }       Range[PCI_TYPE2_ADDRESSES-1];
            UCHAR   InterruptLine;
            UCHAR   InterruptPin;
            USHORT  BridgeControl;
        } type2;
    } u;
} PCI_COMMON_HEADER, *PPCI_COMMON_HEADER;

Depending on the value in HeaderType, one of the three unions (type0, type1 or type2) is the "correct" one to be used.

toxcct8-Oct-07 3:11

toxcct

8-Oct-07 3:11

i used to use it when programming microcontrolers in my electronic classes... i had some devices sharing the same memory address with different registers, for which the union is the exact logical representation then...

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Nemanja Trifunovic8-Oct-07 2:57

Nemanja Trifunovic

8-Oct-07 2:57

chandu004 wrote:
some example

For instance, the winsock implementation of the in_addr Structure[^]

Programming Blog
utf8-cpp

ShilpiP8-Oct-07 1:52

ShilpiP

8-Oct-07 1:52

A structure is a collection of items of different types; and each data item will have its own memory location. Where as only one item within the union can be used at any time, because the memory allocated for each item inside the union is in a shared memory location i.e., only one memory location will be shared by the data items of union.

Size of union will be the size of the biggest variable.
For eg
#include "stdafx.h"
struct s
{
int i;
char ch;
float f;
};
union u
{
int i;
char ch;
float f;
};
int main(int argc, char* argv[])
{
printf("Hello World!\n");
s s1;
u u1;
printf("%d %d",sizeof(s1),sizeof(u1));
return 0;
}

than result is 12 and 4 .I think now it is clear for u.

Yes U Can ...If U Can ,Dream it , U can do it ...ICAN

pointers

KASR17-Oct-07 23:46

7-Oct-07 23:46

What is the difference between 'constant pointer' and 'pointer to a constant'? with example.

Re: pointers

Maxwell Chen8-Oct-07 0:12

Maxwell Chen

8-Oct-07 0:12

Constant pointer can never be advanced.
Pointer to a constant points to a constant object. The target value can never be changed.

Maxwell Chen

Re: pointers

Hamid_RT8-Oct-07 0:31

Constant Pointers And Pointers To Constants[^].

8-Oct-07 0:31

about thread memory space

DSPCottage7-Oct-07 22:22

DSPCottage

7-Oct-07 22:22

Dear All.

in one multi threaded project, we have 15 threads.
We want to restrict any thread to not write data into the memory space of other threads.
How we can do this ?
Is there any document about thread memory space available.

Regards
Monhi

Re: about thread memory space

Matthew Faithfull7-Oct-07 23:03

Matthew Faithfull

7-Oct-07 23:03

Gut Mikh Tappe wrote:
thread memory space

Hmm, under Windows the only Thread specific Memory Space is Thread Local Storage (TLS) which is already protected and can't be over written by other threads without some knowledge and some assembly code. Each thread has it's own stack so you don't need to worry about anything stack based. Heap memory, allocated with new, is shared and this you do need to protect. There's no single or simple way to do this, you need to manually keep track of all objects ( I hope your code is OO ) shared between threads. Each of these objects needs protecting using relevant Synchronisation Objects, sometimes called Synchronisation Primitives. Critical Sections, Mutexes, Events, Semaphores and Completion Ports. There is an extensive Synchronisation section of the Win32 API which you can use to create, lock, unlock and free these objects which are implemented by the Windows Kernel. If you use a framework like MFC some or all of these objects may be provided with easy to use wrappers along with useful classes like stack based Mutex Locks. I hope this is enough to get you started.

Nothing is exactly what it seems but everything with seems can be unpicked.

Re: about thread memory space

DSPCottage8-Oct-07 1:35

DSPCottage

8-Oct-07 1:35

Dear Matthew
Do you know any function to lock a space which is allocated by new operator.
Regards

Re: about thread memory space

chandu0048-Oct-07 2:00