C and C++ applications that issue SQL statements

Each SQL statement in a C or C++ program must begin with EXEC SQL and end with a semicolon (;). The EXEC and SQL keywords must appear on one line, but the remainder of the statement can appear on subsequent lines.

In general, because C is case sensitive, use uppercase letters to enter all SQL keywords. However, if you use the FOLD precompiler suboption, Db2 folds lowercase letters in SBCS SQL ordinary identifiers to uppercase. For information about host language precompiler options, see Table 1.

You must keep the case of host variable names consistent throughout the program. For example, if a host variable name is lowercase in its declaration, it must be lowercase in all SQL statements. You might code an UPDATE statement in a C program as follows:

EXEC SQL
   UPDATE DSN8C10.DEPT
   SET MGRNO = :mgr_num
   WHERE DEPTNO = :int_dept;

Comments

You can include C comments (/* ... */) within SQL statements wherever you can use a blank, except between the keywords EXEC and SQL. You can use single-line comments (starting with //) in C language statements, but not in embedded SQL. You can use SQL comments within embedded SQL statements. For more information, see SQL comments.

You can nest comments.

To include EBCDIC DBCS characters in comments, you must delimit the characters by a shift-out and shift-in control character; the first shift-in character in the DBCS string signals the end of the DBCS string.

Continuation for SQL statements

You can use a backslash to continue a character-string constant or delimited identifier on the following line. However, EBCDIC DBCS string constants cannot be continued on a second line.

Delimiters

Delimit an SQL statement in your C program with the beginning keyword EXEC SQL and a Semicolon (;).

Declaring tables and views

Your C program should use the DECLARE TABLE statement to describe each table and view the program accesses. You can use the Db2 declarations generator (DCLGEN) to generate the DECLARE TABLE statements. For more information, see DCLGEN (declarations generator).

Including SQL statements and variable declarations in source code that is to be processed by the Db2 precompiler

To include SQL statements or C host variable declarations from a member of a partitioned data set, add the following SQL statement to the source code where you want to include the statements:

EXEC SQL INCLUDE member-name;

You cannot nest SQL INCLUDE statements. Do not use C #include statements to include SQL statements or C host variable declarations.

Margins

Code SQL statements in columns 1 through 72, unless you specify other margins to the Db2 precompiler. If EXEC SQL is not within the specified margins, the Db2 precompiler does not recognize the SQL statement. The margin rules do not apply to the Db2 coprocessor. The Db2 coprocessor allows variable length source input.

Names

You can use any valid C name for a host variable, subject to the following restrictions:

• Do not use DBCS characters.
• Do not use external entry names or access plan names that begin with 'DSN', and do not use host variable names or macro names that begin with 'SQL' (in any combination of uppercase or lowercase letters). These names are reserved for Db2.

An SQL identifier that starts with the pound character ('#') can be interpreted as a C macro statement.

Nulls and NULs

C and SQL differ in the way they use the word null. The C language has a null character (NUL), a null pointer (NULL), and a null statement (just a semicolon). The C NUL is a single character that compares equal to 0. The C NULL is a special reserved pointer value that does not point to any valid data object. The SQL null value is a special value that is distinct from all non-null values and denotes the absence of a (nonnull) value. NUL (or NUL-terminator) is the null character in C and C++, and NULL is the SQL null value.

Sequence numbers

The Db2 precompiler generates statements without sequence numbers. (The Db2 coprocessor does not perform this action, because the source is read and modified by the compiler. )

Statement labels

You can precede SQL statements with a label.

Trigraph characters

Some characters from the C character set are not available on all keyboards. You can enter these characters into a C source program using a sequence of three characters called a trigraph. The trigraph characters that Db2 supports are the same as those that the C compiler supports.

WHENEVER statement

The target for the GOTO clause in an SQL WHENEVER statement must be within the scope of any SQL statements that the statement WHENEVER affects.

Special C/C++ considerations

• Using the C/370 multi-tasking facility, in which multiple tasks execute SQL statements, causes unpredictable results.
• Except for the Db2 coprocessor, you must run the Db2 precompiler before running the C preprocessor.
• Except for the Db2 coprocessor, Db2 precompiler does not support C preprocessor directives.
• If you use conditional compiler directives that contain C code, either place them after the first C token in your application program, or include them in the C program using the #include preprocessor directive.

Refer to the appropriate C documentation for more information about C preprocessor directives.

To use the decimal floating-point host data type, you must do the following:

• Use z/OS® 1.10 or above (z/OS V1R10 XL C/C++ ).
• Compile with the C/C++ compiler option, DFP.
• Specify the SQL compiler option to enable the Db2 coprocessor.
• Specify C/C++ compiler option, ARCH(7). It is required by the DFP compiler option if the DFP type is used in the source.
• Specify 'DEFINE(__STDC_WANT_DEC_FP__)' compiler option.

Handling SQL error codes

C and C++ applications can request more information about SQL errors from Db2. For more information, see Handling SQL error codes in C and C++ applications.