Error Handling v11

ECPGPlus provides two methods to detect and handle errors in embedded SQL code:

• A client application can examine the sqlca data structure for error messages, and supply customized error handling for your client application.
• A client application can include EXEC SQL WHENEVER directives to instruct the ECPGPlus compiler to add error-handling code.

Error Handling with sqlca

sqlca (SQL communications area) is a global variable used by ecpglib to communicate information from the server to the client application. After executing a SQL statement (for example, an INSERT or SELECT statement) you can inspect the contents of sqlca to determine if the statement has completed successfully or if the statement has failed.

sqlca has the following structure:

struct
{
    char sqlcaid[8];
    long sqlabc;
    long sqlcode;
    struct
    {
        int sqlerrml;
        char sqlerrmc[SQLERRMC_LEN];
    } sqlerrm;
    char sqlerrp[8];
    long sqlerrd[6];
    char sqlwarn[8];
    char sqlstate[5];

} sqlca;

Use the following directive to implement sqlca functionality:

EXEC SQL INCLUDE sqlca;

If you include the ecpg directive, you do not need to #include the sqlca.h file in the client application's header declaration.

The Advanced Server sqlca structure contains the following members:

sqlcaid

sqlcaid contains the string: "SQLCA".

sqlabc

sqlabc contains the size of the sqlca structure.

sqlcode

The sqlcode member has been deprecated with SQL 92; Advanced Server supports sqlcode for backward compatibility, but you should use the sqlstate member when writing new code.

sqlcode is an integer value; a positive sqlcode value indicates that the client application has encountered a harmless processing condition, while a negative value indicates a warning or error.

If a statement processes without error, sqlcode will contain a value of 0. If the client application encounters an error (or warning) during a statement's execution, sqlcode will contain the last code returned.

The SQL standard defines only a positive value of 100, which indicates that he most recent SQL statement processed returned/affected no rows. Since the SQL standard does not define other sqlcode values, please be aware that the values assigned to each condition may vary from database to database.

sqlerrm is a structure embedded within sqlca, composed of two members:

sqlerrml

sqlerrml contains the length of the error message currently stored in sqlerrmc.

sqlerrmc

sqlerrmc contains the null-terminated message text associated with the code stored in sqlstate. If a message exceeds 149 characters in length, ecpglib will truncate the error message.

sqlerrp

sqlerrp contains the string "NOT SET".

sqlerrd is an array that contains six elements:

• sqlerrd[1] contains the OID of the processed row (if applicable).

• sqlerrd[2] contains the number of processed or returned rows.

• sqlerrd[0], sqlerrd[3], sqlerrd[4] and sqlerrd[5] are unused.

sqlwarn is an array that contains 8 characters:

• sqlwarn[0] contains a value of 'W' if any other element within sqlwarn is set to 'W'.

• sqlwarn[1] contains a value of 'W' if a data value was truncated when it was stored in a host variable.

• sqlwarn[2] contains a value of 'W' if the client application encounters a non-fatal warning.

• sqlwarn[3], sqlwarn[4], sqlwarn[5], sqlwarn[6], and sqlwarn[7] are unused.

sqlstate

sqlstate is a 5 character array that contains a SQL-compliant status code after the execution of a statement from the client application. If a statement processes without error, sqlstate will contain a value of 00000. Please note that sqlstate is not a null-terminated string.

sqlstate codes are assigned in a hierarchical scheme:

• The first two characters of sqlstate indicate the general class of the condition.
• The last three characters of sqlstate indicate a specific status within the class.

If the client application encounters multiple errors (or warnings) during an SQL statement's execution sqlstate will contain the last code returned.

The following table lists the sqlstate and sqlcode values, as well as the symbolic name and error description for the related condition:

EXEC SQL WHENEVER

Use the EXEC SQL WHENEVER directive to implement simple error handling for client applications compiled with ECPGPlus. The syntax of the directive is:

EXEC SQL WHENEVER <condition> <action>;

This directive instructs the ECPG compiler to insert error-handling code into your program.

The code instructs the client application that it should perform a specified action if the client application detects a given condition. The condition may be one of the following:

SQLERROR

A SQLERROR condition exists when sqlca.sqlcode is less than zero.

SQLWARNING

A SQLWARNING condition exists when sqlca.sqlwarn[0] contains a 'W'.

NOT FOUND

A NOT FOUND condition exists when sqlca.sqlcode is ECPG_NOT_FOUND (when a query returns no data).

You can specify that the client application perform one of the following actions if it encounters one of the previous conditions:

CONTINUE

Specify CONTINUE to instruct the client application to continue processing, ignoring the current condition. CONTINUE is the default action.

DO CONTINUE

An action of DO CONTINUE will generate a CONTINUE statement in the emitted C code that if it encounters the condition, skips the rest of the code in the loop and continues with the next iteration. You can only use it within a loop.

GOTO label

or

GO TO label

Use a C goto statement to jump to the specified label.

SQLPRINT

Print an error message to stderr (standard error), using the sqlprint() function. The sqlprint() function prints sql error, followed by the contents of sqlca.sqlerrm.sqlerrmc.

STOP

Call exit(1) to signal an error, and terminate the program.

DO BREAK

Execute the C break statement. Use this action in loops, or switch statements.

CALL name(args)

or

DO name(args)

Invoke the C function specified by the name parameter, using the parameters specified in the args parameter.

Example:

The following code fragment prints a message if the client application encounters a warning, and aborts the application if it encounters an error:

EXEC SQL WHENEVER SQLWARNING SQLPRINT;
EXEC SQL WHENEVER SQLERROR STOP;

• On this page
• Error Handling with sqlca
• EXEC SQL WHENEVER