vcg19.htm

Visual C++与数据库的连接经典实例

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<LI>Novell's IPX ODI protocol is also supported. This protocol lets a Windows 95 user access Novell networks using two protocols&#151;Novell's IPX ODI or Microsoft's IPX/SPX protocol.

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<LI>SunSoft's SunSelect PC-NFS protocol is also supported, allowing you to connect to SunSoft servers. Currently, the SunSelect network isn't commonly used.

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<P>Although Windows NT Server supports the TCP/IP protocol that is used primarily by UNIX applications, there is no provision in Windows NT Server for connecting to Network File System (NFS) servers that let UNIX and DOS/Windows applications share a common set of files. NFS was developed by Sun Microsystems, Inc., in 1983 for use with Sun UNIX workstations. Sun offers PC-NFS, an add-in application for Windows 3.1 and WfWg clients that provides NFS connectivity in Ethernet environments.

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<FONT SIZE=4 COLOR="#FF0000"><B>TCP/IP in Windows NT Server 3.51 and Windows NT Workstation 3.51</B></FONT></CENTER></H5>

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<P>TCP/IP is rapidly attaining the status of a <I>de facto</I> protocol standard for wide-area communication between local-area networks. Most firms that have heterogeneous LANs (LANs that support a variety of workstation types or transport protocols) also use TCP/IP as their primary LAN transport protocol. Virtually all mainframes, minicomputers, RISC workstations, and PC operating systems support TCP/IP, at least over Ethernet cabling. Thus, if you're developing Visual C++ database applications for large organizations, it's likely that you'll need to deal with TCP/IP.

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<NOTE><B>NOTE</B>

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<BR>Included with Windows NT Server is the Microsoft Windows NT Server TCP/IP manual. This document describes Windows NT's implementation of TCP/IP.</NOTE>

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<P>TCP/IP is a connection-oriented protocol that is made up of two protocols&#151;TCP and IP. The IP protocol establishes a connection between two devices on a network, based on 4-byte (32-bit) addresses; inclusion of the IP address makes TCP/IP a routable protocol. The IP address is represented by the decimal values of each of the four bytes of the address, separated by periods, as in 115.27.88.33, which corresponds to 0x731B5821 in Visual C++ hexadecimal notation. The IP address consists of the following two components:

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<LI>A system network ID that identifies groups of devices (hosts) that are located on the same network

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<LI>A system host ID that identifies a particular device on the network, such as a workstation or a server, with the specified network ID

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<P>A second 4-byte value, called the <I>subnet mask,</I> specifies which bytes of the IP address are to be interpreted as the network ID and which are host ID values. You create a subnet mask by creating a 32-bit binary value that has bits that are set to 1 in positions corresponding to the network ID byte(s) and to 0 in positions representing the host ID byte(s). Thus, a subnet mask with a value of 255.255.0.0 (0xFFFF0000) applied to the IP address used in the preceding example specifies that the network ID is 115.27 and the host ID is 88.33.

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<NOTE><B>NOTE</B>

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<BR>An address with a 2-byte network ID and a 2-byte host ID is called a class B network address. A 1-byte network ID and 3-byte host ID is a class A address. A 3-byte network ID and 1-byte host ID is a class C address. Using different address classes lets you determine how many individual networks can be addressed. As you assign more bytes to network addresses, the number of devices allowed on each network decreases. All computers connected on a single network must use the same network ID and subnet mask.</NOTE>

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<P>After the connection is created between the two network devices specified by the IP address and subnet mask, TCP creates individual IP packets from the data to be transmitted. Each packet has a header that includes the following information:

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<LI>A port ID that identifies the application running on the transmitting device.

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<LI>A checksum that is used to verify that the packet was transmitted without error. If an error occurs, the packet is retransmitted.

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<LI>A sequence number that lets the receiving device reassemble the packets into a stream of received data that is identical to the original transmitted data.

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<LI>Other control information related to the type of data and the transmitting application.

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<P>Windows NT Server provides the following 17 basic utility services that are associated with the TCP/IP network protocol.

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<NOTE><B>NOTE</B>

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<BR>To obtain help on one of the TCP/IP utilities, enter the command with the help option (-?). For example, arp -? gives you help information about the options for the arp utility.</NOTE>

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<P><B>WARNING</B>

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<BR>Utilities such as ftp, ftpsvc, rexec, and telnet require the use of passwords. The password is sent to the host system in an unencrypted (plain-text) form. I strongly recommend that you make sure these passwords are unique and different from the passwords used on the local Windows NT network for users, domains, and workgroups.

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<LI>The arp utility is used to display and modify the IP-to-Ethernet of token-ring physical address translation tables that are used by the Address Resolution Protocol (ARP). You can choose to display the current entries (all entries or those based on a specific interface), delete an entry, or add an entry.

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<LI>The finger utility is a connectivity command that is used to display information about a user who is on a specific system that is running the finger service. The output of the finger utility varies depending on the remote systems responses.

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<LI>The ftp utility uses the file transfer protocols to let you send and receive files over TCP/IP networks with File Transfer Protocol (FTP) and Trivial File Transfer Protocol (TFTP). Both of these protocols use the Windows NT command line. The ftp utility can take its input either directly from the command line or from an ASCII text file. Anonymous FTP, one mode of which lets you use Anonymous as the user name and usually your e-mail address as the password, is the most common method of transferring text and binary files over the Internet.

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<LI>The hostname command is used to display the name of the current TCP/IP host. This command has no options.

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<LI>The ipconfig utility is used for diagnostics. It displays information about the configuration of the current machine. This utility is most useful on systems that are running Dynamic Host Configuration Protocol (DHCP) servers.

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<LI>The lpq utility is used to obtain the status of a specific printer queue on a specific server. An option lets you obtain detailed status information.

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<LI>The lpr utility lets you print a file to a host system that is running as an LPD server.

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<LI>The nbtstat command is used to display statistics about the protocol and the current TCP/IP connection. You use this command when you're using NetBIOS over TCP/IP.

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<LI>The ping utility can be used to verify the connections to one or more remote hosts. The connection is verified by having the host send one or more ECHO packets to the client. The ping utility returns information that can be used to estimate the performance of the connection to the host.

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<LI>The rcp command can be used to copy files between the Windows NT system and a remote system running rshd (remote shell server). You can also copy files between two other systems running rshd when you issue the rcp command from the Windows NT system.

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<LI>The rexec command lets a user run a command on a remote host that is running the rexecd service. This command will authenticate the user's name on the remote system (by using a password) before executing the command.

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<LI>The route utility is used to manage and modify the network routing tables. With the route utility you can print, add, delete, or change routing.

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<LI>The rsh command is used to run commands on hosts that are running the RSH (Remote Process Execution) service. This command is similar to the rexec command.

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<LI>The snmp (Simple Network Management Protocol) utility reports the current status of a server or workstation on a network. Using snmp, you can specify the communities and host(s) from which the server or workstation will accept requests for network status information and send an authentication trap (request for identification) when an unspecified