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| Pro*C/C++ Precompiler Programmer's Guide Release 8.0 A58233-01 |
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An application program must anticipate runtime errors and attempt to recover from them. This chapter provides an in-depth discussion of error reporting and recovery. You learn how to handle errors and status changes using the SQLSTATE status variable, as well as the SQL Communications Area (SQLCA) and the WHENEVER statement. You also learn how to diagnose problems using the Oracle Communications Area (ORACA). The following topics are discussed:
A significant part of every application program must be devoted to error handling. The main reason for error handling is that it allows your program to continue operating in the presence of errors. Errors arise from design faults, coding mistakes, hardware failures, invalid user input, and many other sources.
You cannot anticipate all possible errors, but you can plan to handle certain kinds of errors meaningful to your program. For the Pro*C/C++ Precompiler, error handling means detecting and recovering from SQL statement execution errors.
You can also prepare to handle warnings such as "value truncated" and status changes such as "end of data."
It is especially important to check for error and warning conditions after every SQL data manipulation statement, because an INSERT, UPDATE, or DELETE statement might fail before processing all eligible rows in a table.
There are several alternatives that you can use to detect errors and status changes in the application. This chapter describes these alternatives, however, no specific recommendations are made about what method you should use. The method is, after all, dictated by the design of the application program or tool that you are building.
You can declare a separate status variable, SQLSTATE or SQLCODE, examine its value after each executable SQL statement, and take appropriate action. The action might be calling an error-reporting function, then exiting the program if the error is unrecoverable. Or, you might be able to adjust data, or control variables, and retry the action. See the sections "The SQLSTATE Status Variable" on page 11-3 and the "Declaring SQLCODE" on page 11-14 in this chapter for complete information about these status variables.
Another alternative that you can use is to include the SQL Communications Area structure (sqlca) in your program. This structure contains components that are filled in at runtime after the SQL statement is processed by Oracle.
Note: In this guide, the sqlca structure is commonly referred to using the acronym for SQL Communications Area (SQLCA). When this guide refers to a specific component in the C struct, the structure name (sqlca) is used.
The SQLCA is defined in the header file sqlca.h, which you include in your program using either of the following statements:
Oracle updates the SQLCA after every executable SQL statement. (SQLCA values are unchanged after a declarative statement.) By checking Oracle return codes stored in the SQLCA, your program can determine the outcome of a SQL statement. This can be done in the following two ways:
You can use WHENEVER statements, code explicit checks on SQLCA components, or do both.
The most frequently-used components in the SQLCA are the status variable (sqlca.sqlcode), and the text associated with the error code (sqlca.sqlerrm.sqlerrmc). Other components contain warning flags and miscellaneous information about the processing of the SQL statement. For complete information about the SQLCA structure, see the "Using the SQL Communications Area (SQLCA)" on page 11-16.
Note: SQLCODE (upper case) always refers to a separate status variable, not a component of the SQLCA. SQLCODE is declared as a long integer. When referring to the component of the SQLCA named sqlcode, the fully-qualified name sqlca.sqlcode is always used.
When more information is needed about runtime errors than the SQLCA provides, you can use the ORACA. The ORACA is a C struct that handles Oracle communication. It contains cursor statistics, information about the current SQL statement, option settings, and system statistics. See the "Using the Oracle Communications Area (ORACA)" on page 11-34 for complete information about the ORACA.
The precompiler command line option MODE governs ANSI/ISO compliance. When MODE=ANSI, declaring the SQLCA data structure is optional. However, you must declare a separate status variable named SQLCODE. SQL92 specifies a similar status variable named SQLSTATE, which you can use with or without SQLCODE.
After executing a SQL statement, the Oracle Server returns a status code to the SQLSTATE variable currently in scope. The status code indicates whether the SQL statement executed successfully or raised an exception (error or warning condition). To promote interoperability (the ability of systems to exchange information easily), SQL92 predefines all the common SQL exceptions.
Unlike SQLCODE, which stores only error codes, SQLSTATE stores error and warning codes. Furthermore, the SQLSTATE reporting mechanism uses a standardized coding scheme. Thus, SQLSTATE is the preferred status variable. Under SQL92, SQLCODE is a "deprecated feature" retained only for compatibility with SQL89 and likely to be removed from future versions of the standard.
When MODE=ANSI, you must declare SQLSTATE or SQLCODE. Declaring the SQLCA is optional. When MODE=ORACLE, if you declare SQLSTATE, it is not used.
Unlike SQLCODE, which stores signed integers and can be declared outside the Declare Section, SQLSTATE stores 5-character null-terminated strings and must be declared inside the Declare Section. You declare SQLSTATE as
char SQLSTATE[6]; /* Upper case is required. */Note: SQLSTATE must be declared with a dimension of exactly 6 characters.
SQLSTATE status codes consist of a 2-character class code followed by a 3-character subclass code. Aside from class code 00 ("successful completion"), the class code denotes a category of exceptions. And, aside from subclass code 000 ("not applicable"), the subclass code denotes a specific exception within that category. For example, the SQLSTATE value `22012' consists of class code 22 ("data exception") and subclass code 012 ("division by zero").
Each of the five characters in a SQLSTATE value is a digit (0..9) or an uppercase Latin letter (A..Z). Class codes that begin with a digit in the range 0..4 or a letter in the range A..H are reserved for predefined conditions (those defined in SQL92). All other class codes are reserved for implementation-defined conditions. Within predefined classes, subclass codes that begin with a digit in the range 0..4 or a letter in the range A..H are reserved for predefined subconditions. All other subclass codes are reserved for implementation-defined subconditions. Figure 11-1 shows the coding scheme.
Table 11-1 shows the classes predefined by SQL92.
Note: The class code HZ is reserved for conditions defined in International Standard ISO/IEC DIS 9579-2, Remote Database Access.
Table 11-2 shows how SQLSTATE status codes and conditions are mapped to Oracle errors. Status codes in the range 60000 . 99999 are implementation-defined.
The following rules apply to using SQLSTATE with SQLCODE or the SQLCA when you precompile with the option setting MODE=ANSI. SQLSTATE must be declared inside a Declare Section; otherwise, it is ignored.
You can learn the outcome of the most recent executable SQL statement by checking SQLSTATE explicitly with your own code or implicitly with the WHENEVER SQLERROR statement. Check SQLSTATE only after executable SQL statements and PL/SQL statements.
When MODE=ANSI, and you have not declared a SQLSTATE status variable, you must declare a long integer variable named SQLCODE inside or outside the Declare Section. An example follows:
/* declare host variables */ EXEC SQL BEGIN DECLARE SECTION; int emp_number, dept_number; char emp_name[20]; EXEC SQL END DECLARE SECTION; /* declare status variable--must be upper case */ long SQLCODE;
When MODE=ORACLE, if you declare SQLCODE, it is not used.
You can declare more than one SQLCODE. Access to a local SQLCODE is limited by its scope within your program.
After every SQL operation, Oracle returns a status code to the SQLCODE currently in scope. So, your program can learn the outcome of the most recent SQL operation by checking SQLCODE explicitly, or implicitly with the WHENEVER statement.
When you declare SQLCODE instead of the SQLCA in a particular compilation unit, the precompiler allocates an internal SQLCA for that unit. Your host program cannot access the internal SQLCA. If you declare the SQLCA and SQLCODE, Oracle returns the same status code to both after every SQL operation.
Error reporting depends on variables in the SQLCA. This section highlights the key components of error reporting. The next section takes a close look at the SQLCA.
Every executable SQL statement returns a status code to the SQLCA variable sqlcode, which you can check implicitly with the WHENEVER statement or explicitly with your own code.
A zero status code means that Oracle executed the statement without detecting an error or exception. A positive status code means that Oracle executed the statement but detected an exception. A negative status code means that Oracle did not execute the SQL statement because of an error.
Warning flags are returned in the SQLCA variables sqlwarn[0] through sqlwarn[7], which you can check implicitly or explicitly. These warning flags are useful for runtime conditions not considered errors by Oracle. If no indicator variable is available, Oracle issues an error message.
The number of rows processed by the most recently executed SQL statement is returned in the SQLCA variable sqlca.sqlerrd[2], which you can check explicitly.
Strictly speaking, this variable is not for error reporting, but it can help you avoid mistakes. For example, suppose you expect to delete about ten rows from a table. After the deletion, you check sqlca.sqlerrd[2] and find that 75 rows were processed. To be safe, you might want to roll back the deletion and examine your WHERE-clause search condition.
Before executing a SQL statement, Oracle must parse it, that is, examine it to make sure it follows syntax rules and refers to valid database objects. If Oracle finds an error, an offset is stored in the SQLCA variable sqlca.sqlerrd[4], which you can check explicitly. The offset specifies the character position in the SQL statement at which the parse error begins. As in a normal C string, the first character occupies position zero. For example, if the offset is 9, the parse error begins at the 10th character.
By default, static SQL statements are checked for syntactic errors at precompile time. So, sqlca.sqlerrd[4] is most useful for debugging dynamic SQL statements, which your program accepts or builds at run time.
Parse errors arise from missing, misplaced, or misspelled keywords, invalid options, nonexistent tables, and the like. For example, the dynamic SQL statement
"UPDATE emp SET jib = :job_title WHERE empno = :emp_number"
causes the parse error
ORA-00904: invalid column name
because the column name JOB is misspelled. The value of sqlca.sqlerrd[4] is 15 because the erroneous column name JIB begins at the 16th character.
If your SQL statement does not cause a parse error, Oracle sets sqlca.sqlerrd[4] to zero. Oracle also sets sqlca.sqlerrd[4] to zero if a parse error begins at the first character (which occupies position zero). So, check sqlca.sqlerrd[4] only if sqlca.sqlcode is negative, which means that an error has occurred.
The error code and message for Oracle errors are available in the SQLCA variable SQLERRMC. At most, the first 70 characters of text are stored. To get the full text of messages longer than 70 characters, you use the sqlglm() function. See the section "Getting the Full Text of Error Messages" on page 11-23.
The SQLCA is a data structure. Its components contain error, warning, and status information updated by Oracle whenever a SQL statement is executed. Thus, the SQLCA always reflects the outcome of the most recent SQL operation. To determine the outcome, you can check variables in the SQLCA.
Your program can have more than one SQLCA. For example, it might have one global SQLCA and several local ones. Access to a local SQLCA is limited by its scope within the program. Oracle returns information only to the SQLCA that is in scope.
Note: When your application uses SQL*Net to access a combination of local and remote databases concurrently, all the databases write to one SQLCA. There is not a different SQLCA for each database. For more information, see the section "Concurrent Connections" on page 4-23.
When MODE=ORACLE, declaring the SQLCA is required. To declare the SQLCA, you should copy it into your program with the INCLUDE or #include statement, as follows:
EXEC SQL INCLUDE SQLCA;
or
#include <sqlca.h>
If you use a Declare Section, the SQLCA must be declared outside the Declare Section. Not declaring the SQLCA results in compile-time errors.
When you precompile your program, the INCLUDE SQLCA statement is replaced by several variable declarations that allow Oracle to communicate with the program.
When MODE=ANSI, declaring the SQLCA is optional. But in this case you must declare a SQLCODE or SQLSTATE status variable. The type of SQLCODE (upper case is required) is long. If you declare SQLCODE or SQLSTATE instead of the SQLCA in a particular compilation unit, the precompiler allocates an internal SQLCA for that unit. Your Pro*C/C++ program cannot access the internal SQLCA. If you declare the SQLCA and SQLCODE, Oracle returns the same status code to both after every SQL operation.
Note: Declaring the SQLCA is optional when MODE=ANSI, but you cannot use the WHENEVER SQLWARNING statement without the SQLCA. So, if you want to use the WHENEVER SQLWARNING statement, you must declare the SQLCA.
Note: This Guide uses SQLCODE when referring to the SQLCODE status variable, and sqlca.sqlcode when explicitly referring to the component of the SQLCA structure.
The SQLCA contains the following runtime information about the outcome of SQL statements:
The sqlca.h header file is:
/* NAME SQLCA : SQL Communications Area. FUNCTION Contains no code. Oracle fills in the SQLCA with status info during the execution of a SQL stmt. NOTES ************************************************************** *** *** *** This file is SOSD. Porters must change the data types *** *** appropriately on their platform. See notes/pcport.doc *** *** for more information. *** *** *** ************************************************************** If the symbol SQLCA_STORAGE_CLASS is defined, then the SQLCA will be defined to have this storage class. For example: #define SQLCA_STORAGE_CLASS extern will define the SQLCA as an extern. If the symbol SQLCA_INIT is defined, then the SQLCA will be statically initialized. Although this is not necessary in order to use the SQLCA, it is a good programing practice not to have unitialized variables. However, some C compilers/OS's don't allow automatic variables to be initialized in this manner. Therefore, if you are INCLUDE'ing the SQLCA in a place where it would be an automatic AND your C compiler/OS doesn't allow this style of initialization, then SQLCA_INIT should be left undefined -- all others can define SQLCA_INIT if they wish. If the symbol SQLCA_NONE is defined, then the SQLCA variable will not be defined at all. The symbol SQLCA_NONE should not be defined in source modules that have embedded SQL. However, source modules that have no embedded SQL, but need to manipulate a sqlca struct passed in as a parameter, can set the SQLCA_NONE symbol to avoid creation of an extraneous sqlca variable. */ #ifndef SQLCA #define SQLCA 1 struct sqlca { /* ub1 */ char sqlcaid[8]; /* b4 */ long sqlabc; /* b4 */ long sqlcode; struct { /* ub2 */ unsigned short sqlerrml; /* ub1 */ char sqlerrmc[70]; } sqlerrm; /* ub1 */ char sqlerrp[8]; /* b4 */ long sqlerrd[6]; /* ub1 */ char sqlwarn[8]; /* ub1 */ char sqlext[8]; }; #ifndef SQLCA_NONE #ifdef SQLCA_STORAGE_CLASS SQLCA_STORAGE_CLASS struct sqlca sqlca #else struct sqlca sqlca #endif #ifdef SQLCA_INIT = { {'S', 'Q', 'L', 'C', 'A', ' ', ' ', ' '}, sizeof(struct sqlca), 0, { 0, {0}}, {'N', 'O', 'T', ' ', 'S', 'E', 'T', ' '}, {0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0} } #endif ; #endif #endif
This section describes the structure of the SQLCA, its components, and the values they can store.
This string component is initialized to "SQLCA" to identify the SQL Communications Area.
This integer component holds the length, in bytes, of the SQLCA structure.
This integer component holds the status code of the most recently executed SQL statement. The status code, which indicates the outcome of the SQL operation, can be any of the following numbers
:
When MODE=ANSI, +100 is returned to sqlcode after an INSERT of no rows. This can happen when a subquery returns no rows to process.
Negative return codes correspond to error codes listed in Oracle8 Error Messages.
This embedded struct contains the following two components:
This component can store up to 70 characters. To get the full text of messages longer than 70 characters, you must use the sqlglm function (discussed later).
Make sure sqlcode is negative before you reference sqlerrmc. If you reference sqlerrmc when sqlcode is zero, you get the message text associated with a prior SQL statement.
This string component is reserved for future use.
This array of binary integers has six elements. Descriptions of the components in sqlerrd follow:
The rows-processed count is zeroed after an OPEN statement and incremented after a FETCH statement. For the EXECUTE, INSERT, UPDATE, DELETE, and SELECT INTO statements, the count reflects the number of rows processed successfully. The count does not include rows processed by an UPDATE or DELETE CASCADE. For example, if 20 rows are deleted because they meet WHERE-clause criteria, and 5 more rows are deleted because they now (after the primary delete) violate column constraints, the count is 20 not 25.
This array of single characters has eight elements. They are used as warning flags. Oracle sets a flag by assigning it a "W" (for warning) character value.
The flags warn of exceptional conditions. For example, a warning flag is set when Oracle assigns a truncated column value to an output host variable.
Descriptions of the components in sqlwarn follow:
To find out if a column value was truncated and by how much, check the indicator variable associated with the output host variable. The (positive) integer returned by an indicator variable is the original length of the column value. You can increase the length of the host variable accordingly.
This string component is reserved for future use.
When the precompiler application executes an embedded PL/SQL block, not all components of the SQLCA are set. For example, if the block fetches several rows, the rows-processed count (sqlerrd[2]) is set to only 1. You should depend only on the sqlcode and sqlerrm components of the SQLCA after execution of a PL/SQL block.
The SQLCA can accommodate error messages up to 70 characters long. To get the full text of longer (or nested) error messages, you need the sqlglm function. The syntax of the sqlglm() is
void sqlglm(char *message_buffer, size_t *buffer_size, size_t *message_length);
where:
Note: The types of the last two arguments for the sqlglm() function are shown here generically as size_t pointers. However on your platform they might have a different type. For example, on many UNIX workstation ports, they are unsigned int *.
You should check the file sqlcpr.h, which is in the standard include directory on your system, to determine the datatype of these parameters.
The maximum length of an Oracle error message is 512 characters including the error code, nested messages, and message inserts such as table and column names. The maximum length of an error message returned by sqlglm depends on the value you specify for buffer_size.
The following example calls sqlglm to get an error message of up to 200 characters in length:
EXEC SQL WHENEVER SQLERROR DO sql_error(); ... /* other statements */ ... sql_error() { char msg[200]; size_t buf_len, msg_len; buf_len = sizeof (msg); sqlglm(msg, &buf_len, &msg_len); /* note use of pointers */ printf("%.*s\n\n", msg_len, msg); exit(1); }
Notice that sqlglm is called only when a SQL error has occurred. Always make sure SQLCODE (or sqlca.sqlcode) is non-zero before calling sqlglm. If you call sqlglm when SQLCODE is zero, you get the message text associated with a prior SQL statement.
By default, precompiled programs ignore Oracle error and warning conditions and continue processing if possible. To do automatic condition checking and error handling, you need the WHENEVER statement.
With the WHENEVER statement you can specify actions to be taken when Oracle detects an error, warning condition, or "not found" condition. These actions include continuing with the next statement, calling a routine, branching to a labeled statement, or stopping.
You code the WHENEVER statement using the following syntax:
EXEC SQL WHENEVER <condition> <action>;
You can have Oracle automatically check the SQLCA for any of the following conditions.
sqlwarn[0] is set because Oracle returned a warning (one of the warning flags, sqlwarn[1] through sqlwarn[7], is also set) or SQLCODE has a positive value other than +1403. For example, sqlwarn[0] is set when Oracle assigns a truncated column value to an output host variable.
Declaring the SQLCA is optional when MODE=ANSI. To use WHENEVER SQLWARNING, however, you must declare the SQLCA.
SQLCODE has a negative value because Oracle returned an error.
SQLCODE has a value of +1403 (+100 when MODE=ANSI) because Oracle could not find a row that meets your WHERE-clause search condition, or a SELECT INTO or FETCH returned no rows.
When MODE=ANSI, +100 is returned to SQLCODE after an INSERT of no rows.
When Oracle detects one of the preceding conditions, you can have your program take any of the following actions.
Your program continues to run with the next statement if possible. This is the default action, equivalent to not using the WHENEVER statement. You can use it to turn off condition checking.
Your program transfers control to an error handling function in the program. When the end of the routine is reached, control transfers to the statement that follows the failed SQL statement.
The usual rules for entering and exiting a function apply. You can pass parameters to the error handler invoked by an EXEC SQL WHENEVER ... DO ... statement, and the function can return a value.
An actual "break" statement is placed in your program. Use this action in loops.When the WHENEVER condition is met, your program exits the loop it is inside.
An actual "continue" statement is placed in your program. Use this action in loops. When the WHENEVER condition is met, your program continues with the next iteration of the loop it is inside.
Your program branches to a labeled statement.
Your program stops running and uncommitted work is rolled back.
STOP in effect just generates an exit() call whenever the condition occurs. Be careful. The STOP action displays no messages before disconnecting from Oracle.
If you want your program to
simply code the following WHENEVER statements before the first executable SQL statement:
EXEC SQL WHENEVER NOT FOUND GOTO close_cursor; EXEC SQL WHENEVER SQLWARNING CONTINUE; EXEC SQL WHENEVER SQLERROR GOTO error_handler;
In the following example, you use WHENEVER...DO statements to handle specific errors:
... EXEC SQL WHENEVER SQLERROR DO handle_insert_error("INSERT error"); EXEC SQL INSERT INTO emp (empno, ename, deptno) VALUES (:emp_number, :emp_name, :dept_number); EXEC SQL WHENEVER SQLERROR DO handle_delete_error("DELETE error"); EXEC SQL DELETE FROM dept WHERE deptno = :dept_number; ... handle_insert_error(char *stmt) { switch(sqlca.sqlcode) { case -1: /* duplicate key value */ ... break; case -1401: /* value too large */ ... break; default: /* do something here too */ ... break; } } handle_delete_error(char *stmt) { printf("%s\n\n", stmt); if (sqlca.sqlerrd[2] == 0) { /* no rows deleted */ ... } else { ... } ... }
Notice how the procedures check variables in the SQLCA to determine a course of action.
This example illustrates how to display employee name, salary, and commission for only those employees who receive commissions:
#include <sqlca.h>#include <stdio.h>main(){ char *uid = "scott/tiger"; struct { char ename[12]; float sal; float comm; } emp; /* Trap any connection error that might occur. */ EXEC SQL WHENEVER SQLERROR GOTO whoops; EXEC SQL CONNECT :uid; EXEC SQL DECLARE c CURSOR FOR SELECT ename, sal, comm FROM EMP ORDER BY ENAME ASC; EXEC SQL OPEN c; /* Set up `BREAK' condition to exit the loop. */ EXEC SQL WHENEVER NOT FOUND DO BREAK; /* The DO CONTINUE makes the loop start at the next iteration when an error occurs.*/ EXEC SQL WHENEVER SQLERRORDO CONTINUE; while (1) { EXEC SQL FETCH c INTO :emp; /* An ORA-1405 would cause the `continue' to occur. So only employees with */ /* non-NULL commissions will be displayed. */ printf("%s %7.2f %9.2f\n", emp.ename, emp.sal, emp.comm); }/* This `CONTINUE' shuts off the `DO CONTINUE' allowing the program to proceed if any further errors do occur, specifically, with the CLOSE */ EXEC SQL WHENEVER SQLERROR CONTINUE; EXEC SQL CLOSE c; exit(EXIT_SUCCESS);whoops: printf("%.*s\n", sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc); exit(EXIT_FAILURE);}
Because WHENEVER is a declarative statement, its scope is positional, not logical. That is, it tests all executable SQL statements that physically follow it in the source file, not in the flow of program logic. So, code the WHENEVER statement before the first executable SQL statement you want to test.
A WHENEVER statement stays in effect until superseded by another WHENEVER statement checking for the same condition.
In the example below, the first WHENEVER SQLERROR statement is superseded by a second, and so applies only to the CONNECT statement. The second WHENEVER SQLERROR statement applies to both the UPDATE and DROP statements, despite the flow of control from step1 to step3.
step1: EXEC SQL WHENEVER SQLERROR STOP; EXEC SQL CONNECT :username IDENTIFIED BY :password; ... goto step3; step2: EXEC SQL WHENEVER SQLERROR CONTINUE; EXEC SQL UPDATE emp SET sal = sal * 1.10; ... step3: EXEC SQL DROP INDEX emp_index; ...
The following guidelines will help you avoid some common pitfalls.
In general, code a WHENEVER statement before the first executable SQL statement in your program. This ensures that all ensuing errors are trapped because WHENEVER statements stay in effect to the end of a file.
Your program should be prepared to handle an end-of-data condition when using a cursor to fetch rows. If a FETCH returns no data, the program should exit the fetch loop, as follows:
EXEC SQL WHENEVER NOT FOUND DO break; for (;;) { EXEC SQL FETCH... } EXEC SQL CLOSE my_cursor; ...
If a WHENEVER SQLERROR GOTO statement branches to an error handling routine that includes an executable SQL statement, your program might enter an infinite loop if the SQL statement fails with an error. You can avoid this by coding WHENEVER SQLERROR CONTINUE before the SQL statement, as shown in the following example:
EXEC SQL WHENEVER SQLERROR GOTO sql_error; ... sql_error: EXEC SQL WHENEVER SQLERROR CONTINUE; EXEC SQL ROLLBACK WORK RELEASE; ...
Without the WHENEVER SQLERROR CONTINUE statement, a ROLLBACK error would invoke the routine again, starting an infinite loop.
Careless use of WHENEVER can cause problems. For example, the following code enters an infinite loop if the DELETE statement sets NOT FOUND because no rows meet the search condition:
/* improper use of WHENEVER */ ... EXEC SQL WHENEVER NOT FOUND GOTO no_more; for (;;) { EXEC SQL FETCH emp_cursor INTO :emp_name, :salary; ... } no_more: EXEC SQL DELETE FROM emp WHERE empno = :emp_number; ...
The next example handles the NOT FOUND condition properly by resetting the GOTO target:
/* proper use of WHENEVER */ ... EXEC SQL WHENEVER NOT FOUND GOTO no_more; for (;;) { EXEC SQL FETCH emp_cursor INTO :emp_name, :salary; ... } no_more: EXEC SQL WHENEVER NOT FOUND GOTO no_match; EXEC SQL DELETE FROM emp WHERE empno = :emp_number; ... no_match: ...
Make sure all SQL statements governed by a WHENEVER GOTO statement can branch to the GOTO label. The following code results in a compile-time error because labelA in func1 is not within the scope of the INSERT statement in func2:
func1() { EXEC SQL WHENEVER SQLERROR GOTO labelA; EXEC SQL DELETE FROM emp WHERE deptno = :dept_number; ... labelA: ... } func2() { EXEC SQL INSERT INTO emp (job) VALUES (:job_title); ... }
The label to which a WHENEVER GOTO statement branches must be in the same precompilation file as the statement.
If your program must return after handling an error, use the DO routine_call action. Alternatively, you can test the value of sqlcode, as shown in the following example:
... EXEC SQL UPDATE emp SET sal = sal * 1.10; if (sqlca.sqlcode < 0) { /* handle error */ EXEC SQL DROP INDEX emp_index;
Just make sure no WHENEVER GOTO or WHENEVER STOP statement is active.
In many precompiler applications it is convenient to know the text of the statement being processed, its length, and the SQL command (such as INSERT or SELECT) that it contains. This is especially true for applications that use dynamic SQL.
The sqlgls() function-part of the SQLLIB runtime library-returns the following information:
You can call sqlgls() after issuing a static SQL statement. For dynamic SQL Method 1, call sqlgls() after the SQL statement is executed. For dynamic SQL Methods 2, 3, and 4, you can call sqlgls() as soon as the statement has been PREPAREd.
The prototype for sqlgls() is
int sqlgls(char *sqlstm, size_t *stmlen, size_t *sqlfc);
The sqlstm parameter is a character buffer that holds the returned text of the SQL statement. Your program must statically declare the buffer or dynamically allocate memory for the buffer.
The stmlen parameter is a long integer. Before calling sqlgls(), set this parameter to the actual size, in bytes, of the sqlstm buffer. When sqlgls() returns, the sqlstm buffer contains the SQL statement text, blank padded to the length of the buffer. The stmlen parameter returns the actual number of bytes in the returned statement text, not counting blank padding.
The sqlfc parameter is a long integer that returns the SQL function code for the SQL command in the statement. Table 11-3 shows the SQL function codes for the commands.
The sqlgls() function returns an int. The return value is zero (FALSE) if an error occurred, or is one (TRUE) if there was no error. The length parameter (stmlen) returns a zero if an error occurred. Possible error conditions are:
sqlgls() does not return the text for statements that contain the following commands:
There are no SQL function codes for these commands.
The sample program sqlvcp.pc, which is listed in Chapter 3, "Developing a Pro*C/C++ Application", demonstrates how you can use the sqlgls() function. This program is also available on-line, in your demo directory.
The SQLCA handles standard SQL communications; the ORACA handles Oracle communications. When you need more information about runtime errors and status changes than the SQLCA provides, use the ORACA. It contains an extended set of diagnostic tools. However, use of the ORACA is optional because it adds to runtime overhead.
Besides helping you to diagnose problems, the ORACA lets you monitor your program's use of Oracle resources such as the SQL Statement Executor and the cursor cache.
Your program can have more than one ORACA. For example, it might have one global ORACA and several local ones. Access to a local ORACA is limited by its scope within the program. Oracle returns information only to the ORACA that is in scope.
To declare the ORACA, copy it into your program with the INCLUDE statement or the #include preprocessor directive, as follows:
EXEC SQL INCLUDE ORACA;
or
#include <oraca.h>
If your ORACA must be of the extern storage class, define ORACA_STORAGE_CLASS in your program as follows:
#define ORACA_STORAGE_CLASS extern
If the program uses a Declare Section, the ORACA must be defined outside it.
To enable the ORACA, you must specify the ORACA option, either on the command line with
ORACA=YES
or inline with
EXEC ORACLE OPTION (ORACA=YES);
Then, you must choose appropriate runtime options by setting flags in the ORACA.
The ORACA contains option settings, system statistics, and extended diagnostics such as
A partial listing of oraca.h is
/* NAME ORACA : Oracle Communications Area. If the symbol ORACA_NONE is defined, then there will be no ORACA *variable*, although there will still be a struct defined. This macro should not normally be defined in application code. If the symbol ORACA_INIT is defined, then the ORACA will be statically initialized. Although this is not necessary in order to use the ORACA, it is a good pgming practice not to have unitialized variables. However, some C compilers/OS's don't allow automatic variables to be init'd in this manner. Therefore, if you are INCLUDE'ing the ORACA in a place where it would be an automatic AND your C compiler/OS doesn't allow this style of initialization, then ORACA_INIT should be left undefined -- all others can define ORACA_INIT if they wish. */ #ifndef ORACA #define ORACA 1 struct oraca { char oracaid[8]; /* Reserved */ long oracabc; /* Reserved */ /* Flags which are setable by User. */ long oracchf; /* <> 0 if "check cur cache consistncy"*/ long oradbgf; /* <> 0 if "do DEBUG mode checking" */ long orahchf; /* <> 0 if "do Heap consistency check" */ long orastxtf; /* SQL stmt text flag */ #define ORASTFNON 0 /* = don't save text of SQL stmt */ #define ORASTFERR 1 /* = only save on SQLERROR */ #define ORASTFWRN 2 /* = only save on SQLWARNING/SQLERROR */ #define ORASTFANY 3 /* = always save */ struct { unsigned short orastxtl; char orastxtc[70]; } orastxt; /* text of last SQL stmt */ struct { unsigned short orasfnml; char orasfnmc[70]; } orasfnm; /* name of file containing SQL stmt */ long oraslnr; /* line nr-within-file of SQL stmt */ long orahoc; /* highest max open OraCurs requested */ long oramoc; /* max open OraCursors required */ long oracoc; /* current OraCursors open */ long oranor; /* nr of OraCursor re-assignments */ long oranpr; /* nr of parses */ long oranex; /* nr of executes */ }; #ifndef ORACA_NONE #ifdef ORACA_STORAGE_CLASS ORACA_STORAGE_CLASS struct oraca oraca #else struct oraca oraca #endif #ifdef ORACA_INIT = { {'O','R','A','C','A',' ',' ',' '}, sizeof(struct oraca), 0,0,0,0, {0,{0}}, {0,{0}}, 0, 0,0,0,0,0,0 } #endif ; #endif #endif /* end oraca.h */
The ORACA includes several option flags. Setting these flags by assigning them non-zero values allows you to
The descriptions below will help you choose the options you need.
This section describes the structure of the ORACA, its components, and the values they can store.
This string component is initialized to "ORACA" to identify the Oracle Communications Area.
This integer component holds the length, in bytes, of the ORACA data structure.
If the master DEBUG flag (oradbgf) is set, this flag enables the gathering of cursor cache statistics and lets you check the cursor cache for consistency before every cursor operation.
The Oracle runtime library does the consistency checking and might issue error messages, which are listed in the manual Oracle8 Error Messages. They are returned to the SQLCA just like Oracle error messages.
This flag has the following settings:
This master flag lets you choose all the DEBUG options. It has the following settings:
Disable all DEBUG operations (the default).
Enable all DEBUG operations.
If the master DEBUG flag (oradbgf) is set, this flag tells the Oracle runtime library to check the heap for consistency every time the precompiler dynamically allocates or frees memory. This is useful for detecting program bugs that upset memory.
This flag must be set before the CONNECT command is issued and, once set, cannot be cleared; subsequent change requests are ignored. It has the following settings:
This flag lets you specify when the text of the current SQL statement is saved. It has the following settings:
The SQL statement text is saved in the ORACA embedded struct named orastxt.
The ORACA provides an enhanced set of diagnostics; the following variables help you to locate errors quickly.
This embedded struct helps you find faulty SQL statements. It lets you save the text of the last SQL statement parsed by Oracle. It contains the following two components:
Statements parsed by the precompiler, such as CONNECT, FETCH, and COMMIT, are not saved in the ORACA.
This embedded struct identifies the file containing the current SQL statement and so helps you find errors when multiple files are precompiled for one application. It contains the following two components:
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orasfnml |
This integer component holds the length of the filename stored in orasfnmc. |
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orasfnmc |
This string component holds the filename. At most, the first 70 characters are stored. |
This integer component identifies the line at (or near) which the current SQL statement can be found.
If the master DEBUG flag (oradbgf) and the cursor cache flag (oracchf) are set, the variables below let you gather cursor cache statistics. They are automatically set by every COMMIT or ROLLBACK command your program issues.
Internally, there is a set of these variables for each CONNECTed database. The current values in the ORACA pertain to the database against which the last COMMIT or ROLLBACK was executed.
This integer component records the highest value to which MAXOPENCURSORS was set during program execution.
This integer component records the maximum number of open Oracle cursors required by your program. This number can be higher than orahoc if MAXOPENCURSORS was set too low, which forced the precompiler to extend the cursor cache.
This integer component records the current number of open Oracle cursors required by your program.
This integer component records the number of cursor cache reassignments required by your program. This number shows the degree of "thrashing" in the cursor cache and should be kept as low as possible.
This integer component records the number of SQL statement parses required by your program.
This integer component records the number of SQL statement executions required by your program. The ratio of this number to the oranpr number should be kept as high as possible. In other words, avoid unnecessary reparsing. For help, see Appendix C.
The following program prompts for a department number, inserts the name and salary of each employee in that department into one of two tables, then displays diagnostic information from the ORACA. This program is available online in the demo directory, as oraca.pc.
/* oraca.pc * This sample program demonstrates how to * use the ORACA to determine various performance * parameters at runtime. */ #include <stdio.h> #include <string.h> #include <sqlca.h> #include <oraca.h> EXEC SQL BEGIN DECLARE SECTION; char *userid = "SCOTT/TIGER"; char emp_name[21]; int dept_number; float salary; char SQLSTATE[6]; EXEC SQL END DECLARE SECTION; void sql_error(); main() { char temp_buf[32]; EXEC SQL WHENEVER SQLERROR DO sql_error("Oracle error"); EXEC SQL CONNECT :userid; EXEC ORACLE OPTION (ORACA=YES); oraca.oradbgf = 1; /* enable debug operations */ oraca.oracchf = 1; /* gather cursor cache statistics */ oraca.orastxtf = 3; /* always save the SQL statement */ printf("Enter department number: "); gets(temp_buf); dept_number = atoi(temp_buf); EXEC SQL DECLARE emp_cursor CURSOR FOR SELECT ename, sal + NVL(comm,0) AS sal_comm FROM emp WHERE deptno = :dept_number ORDER BY sal_comm DESC; EXEC SQL OPEN emp_cursor; EXEC SQL WHENEVER NOT FOUND DO sql_error("End of data"); for (;;) { EXEC SQL FETCH emp_cursor INTO :emp_name, :salary; printf("%.10s\n", emp_name); if (salary < 2500) EXEC SQL INSERT INTO pay1 VALUES (:emp_name, :salary); else EXEC SQL INSERT INTO pay2 VALUES (:emp_name, :salary); } } void sql_error(errmsg) char *errmsg; { char buf[6]; strcpy(buf, SQLSTATE); EXEC SQL WHENEVER SQLERROR CONTINUE; EXEC SQL COMMIT WORK RELEASE; if (strncmp(errmsg, "Oracle error", 12) == 0) printf("\n%s, sqlstate is %s\n\n", errmsg, buf); else printf("\n%s\n\n", errmsg); printf("Last SQL statement: %.*s\n", oraca.orastxt.orastxtl, oraca.orastxt.orastxtc); printf("\nAt or near line number %d\n", oraca.oraslnr); printf ("\nCursor Cache Statistics\n------------------------\n"); printf ("Maximum value of MAXOPENCURSORS: %d\n", oraca.orahoc); printf ("Maximum open cursors required: %d\n", oraca.oramoc); printf ("Current number of open cursors: %d\n", oraca.oracoc); printf ("Number of cache reassignments: %d\n", oraca.oranor); printf ("Number of SQL statement parses: %d\n", oraca.oranpr); printf ("Number of SQL statement executions: %d\n", oraca.oranex); exit(1); }
