qr barcode generator vb.net Declaring Host Variables in Software

Generating QR Code ISO/IEC18004 in Software Declaring Host Variables

Declaring Host Variables
QR-Code Reader In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Drawing QR Code In None
Using Barcode encoder for Software Control to generate, create Quick Response Code image in Software applications.
When you use a host variable in an embedded SQL statement, you must declare the variable using the normal method for declaring variables in the host programming language. For example, in Figure 17-17, the host variable amount is declared using the normal C language syntax (float amount;). When the precompiler processes the source code for the program, it notes the name of each variable it encounters, along with its data type and size. The precompiler uses this information to generate correct code later when it encounters a use of the variable as a host variable in a SQL statement. The two embedded SQL statements BEGIN DECLARE SECTION and END DECLARE SECTION bracket the host variable declarations, as shown in Figure 17-17. These two statements are unique to embedded SQL, and they are not executable. They are directives to the precompiler, telling it when it must pay attention to variable declarations and when it can ignore them.
Recognizing QR Code In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
QR Code ISO/IEC18004 Drawer In C#
Using Barcode drawer for .NET framework Control to generate, create QR-Code image in VS .NET applications.
17:
Draw QR Code ISO/IEC18004 In .NET
Using Barcode encoder for ASP.NET Control to generate, create QR Code JIS X 0510 image in ASP.NET applications.
Draw QR Code JIS X 0510 In VS .NET
Using Barcode encoder for .NET Control to generate, create QR Code image in VS .NET applications.
Embedded SQL
QR Code ISO/IEC18004 Maker In VB.NET
Using Barcode creation for .NET Control to generate, create Denso QR Bar Code image in .NET applications.
Generate Code 128 Code Set A In None
Using Barcode encoder for Software Control to generate, create Code 128 image in Software applications.
In a simple embedded SQL program, it may be possible to gather together all of the host variable declarations into one declare section. Usually, however, the host variables must be declared at various points within the program, especially in block-structured languages such as C, Pascal, and PL/I. In this case, each declaration of host variables must be bracketed with a BEGIN DECLARE SECTION/END DECLARE SECTION statement pair. The BEGIN DECLARE SECTION and END DECLARE SECTION statements are relatively new to the embedded SQL. They are specified in the ANSI/ISO SQL standard, and DB2 requires them in its newer embedded SQL implementations. However, DB2 and many other DBMS brands did not historically require declare sections, and some SQL precompilers do not yet support the BEGIN DECLARE SECTION and END DECLARE SECTION statements. In this case, the precompiler scans and processes all variable declarations in the host program. When you use a host variable, the precompiler may limit your flexibility in declaring the variable in the host programming language. For example, consider the following C language source code:
Create UPC - 13 In None
Using Barcode encoder for Software Control to generate, create EAN / UCC - 13 image in Software applications.
Barcode Generator In None
Using Barcode generation for Software Control to generate, create bar code image in Software applications.
#define BIGBUFSIZE 256 . . . exec sql begin declare section; char bigbuffer[BIGBUFSIZE+1]; exec sql end declare section;
Draw UCC-128 In None
Using Barcode printer for Software Control to generate, create UCC-128 image in Software applications.
UPCA Generator In None
Using Barcode encoder for Software Control to generate, create GS1 - 12 image in Software applications.
This is a valid C declaration of the variable bigbuffer. However, if you try to use bigbuffer as a host variable in an embedded SQL statement like this:
Encode Identcode In None
Using Barcode generator for Software Control to generate, create Identcode image in Software applications.
Encode Barcode In VS .NET
Using Barcode maker for .NET framework Control to generate, create bar code image in VS .NET applications.
exec sql update salesreps set quota = 300000 where name = :bigbuffer;
Barcode Encoder In None
Using Barcode printer for Font Control to generate, create barcode image in Font applications.
Printing Code 128 Code Set C In None
Using Barcode maker for Office Excel Control to generate, create Code 128 Code Set A image in Office Excel applications.
many precompilers will generate an error message, complaining about an illegal declaration of bigbuffer. The problem is that some precompilers don t recognize symbolic constants like BIGBUFSIZE. This is just one example of the special considerations that apply when using embedded SQL and a precompiler. Fortunately, the precompilers offered by the major DBMS vendors are highly developed, and special-case problems are few.
EAN-13 Creator In None
Using Barcode encoder for Font Control to generate, create EAN 13 image in Font applications.
Decoding EAN / UCC - 13 In .NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in .NET framework applications.
Host Variables and Data Types
Creating UCC - 12 In Java
Using Barcode creation for Java Control to generate, create UCC.EAN - 128 image in Java applications.
Draw UPC A In None
Using Barcode drawer for Font Control to generate, create UPC-A image in Font applications.
PART V
The data types supported by a SQL-based DBMS and the data types supported by a programming language such as C or FORTRAN are often quite different. These differences impact host variables because they play a dual role. On the one hand, a host variable is a program variable, declared using the data types of the programming language and manipulated by programming language statements. On the other hand, a host variable is used in embedded SQL statements to contain database data. Consider the four embedded UPDATE statements in Figure 17-18. In the first UPDATE statement, the MANAGER column has an INTEGER data type, so hostvar1 should be declared as a C integer variable. In the second statement, the NAME column has a VARCHAR data type, so hostvar2 should contain string data. The program should declare hostvar2 as an array of C character data, and most DBMS products will expect the data in the array to
Part V:
Copyright © OnBarcode.com . All rights reserved.