4.6. Error Handling

The embedded SQL interface provides a simplistic and a complex way to handle exceptional conditions in a program. The first method causes a message to printed automatically when a certain condition occurs. For example:

EXEC SQL WHENEVER sqlerror sqlprint;

EXEC SQL WHENEVER not found sqlprint;

This error handling remains enabled throughout the entire program.

Note: This is not an exhaustive example of usage for the EXEC SQL WHENEVER statement. Further examples of usage may be found in SQL manuals (e.g., The LAN TIMES Guide to SQL by Groff and Weinberg).

For a more powerful error handling, the embedded SQL interface provides a struct and a variable with the name sqlca as follows:

struct sqlca
{
    char sqlcaid[8];
    long sqlabc;
    long sqlcode;
    struct
    {
        int sqlerrml;
        char sqlerrmc[70];
    } sqlerrm;
    char sqlerrp[8];

    long sqlerrd[6];
    /* 0: empty                                         */
    /* 1: OID of processed tuple if applicable          */
    /* 2: number of rows processed in an INSERT, UPDATE */
    /*    or DELETE statement                           */
    /* 3: empty                                         */
    /* 4: empty                                         */
    /* 5: empty                                         */

    char sqlwarn[8];
    /* 0: set to 'W' if at least one other is 'W'       */
    /* 1: if 'W' at least one character string          */
    /*    value was truncated when it was               */
    /*    stored into a host variable.                  */
    /* 2: empty                                         */
    /* 3: empty                                         */
    /* 4: empty                                         */
    /* 5: empty                                         */
    /* 6: empty                                         */
    /* 7: empty                                         */

    char sqlext[8];
} sqlca;

(Many of the empty fields may be used in a future release.)

If no error occurred in the last SQL statement, sqlca.sqlcode will be 0 (ECPG_NO_ERROR). If sqlca.sqlcode is less that zero, this is a serious error, like the database definition does not match the query. If it is greater than zero, it is a normal error like the table did not contain the requested row.

sqlca.sqlerrm.sqlerrmc will contain a string that describes the error. The string ends with the line number in the source file.

These are the errors that can occur:

-12, Out of memory in line %d.: Should not normally occur. This indicates your virtual memory is exhausted.
-200 (ECPG_UNSUPPORTED): Unsupported type %s on line %d.: Should not normally occur. This indicates the preprocessor has generated something that the library does not know about. Perhaps you are running incompatible versions of the preprocessor and the library.
-201 (ECPG_TOO_MANY_ARGUMENTS): Too many arguments line %d.: This means that the server has returned more arguments than we have matching variables. Perhaps you have forgotten a couple of the host variables in the INTO :var1,:var2 list.
-202 (ECPG_TOO_FEW_ARGUMENTS): Too few arguments line %d.: This means that the server has returned fewer arguments than we have host variables. Perhaps you have too many host variables in the INTO :var1,:var2 list.
-203 (ECPG_TOO_MANY_MATCHES): Too many matches line %d.: This means the query has returned several rows but the variables specified are not arrays. The SELECT command was not unique.
-204 (ECPG_INT_FORMAT): Not correctly formatted int type: %s line %d.: This means the host variable is of type int and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as an int. The library uses strtol() for this conversion.
-205 (ECPG_UINT_FORMAT): Not correctly formatted unsigned type: %s line %d.: This means the host variable is of type unsigned int and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as an unsigned int. The library uses strtoul() for this conversion.
-206 (ECPG_FLOAT_FORMAT): Not correctly formatted floating-point type: %s line %d.: This means the host variable is of type float and the field in the PostgreSQL database is of another type and contains a value that cannot be interpreted as a float. The library uses strtod() for this conversion.
-207 (ECPG_CONVERT_BOOL): Unable to convert %s to bool on line %d.: This means the host variable is of type bool and the field in the PostgreSQL database is neither 't' nor 'f'.
-208 (ECPG_EMPTY): Empty query line %d.: The query was empty. (This cannot normally happen in an embedded SQL program, so it may point to an internal error.)
-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.: A null value was returned and no null indicator variable was supplied.
-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.: An ordinary variable was used in a place that requires an array.
-211 (ECPG_DATA_NOT_ARRAY): Data read from backend is not an array in line %d.: The database returned an ordinary variable in a place that requires array value.
-220 (ECPG_NO_CONN): No such connection %s in line %d.: The program tried to access a connection that does not exist.
-221 (ECPG_NOT_CONN): Not connected in line %d.: The program tried to access a connection that does exist but is not open.
-230 (ECPG_INVALID_STMT): Invalid statement name %s in line %d.: The statement you are trying to use has not been prepared.
-240 (ECPG_UNKNOWN_DESCRIPTOR): Descriptor %s not found in line %d.: The descriptor specified was not found. The statement you are trying to use has not been prepared.
-241 (ECPG_INVALID_DESCRIPTOR_INDEX): Descriptor index out of range in line %d.: The descriptor index specified was out of range.
-242 (ECPG_UNKNOWN_DESCRIPTOR_ITEM): Descriptor %s not found in line %d.: The descriptor specified was not found. The statement you are trying to use has not been prepared.
-243 (ECPG_VAR_NOT_NUMERIC): Variable is not a numeric type in line %d.: The database returned a numeric value and the variable was not numeric.
-244 (ECPG_VAR_NOT_CHAR): Variable is not a character type in line %d.: The database returned a non-numeric value and the variable was numeric.
-400 (ECPG_PGSQL): Postgres error: %s line %d.: Some PostgreSQL error. The message contains the error message from the PostgreSQL backend.
-401 (ECPG_TRANS): Error in transaction processing line %d.: PostgreSQL signaled that we cannot start, commit, or rollback the transaction.
-402 (ECPG_CONNECT): Could not connect to database %s in line %d.: The connect to the database did not work.
100 (ECPG_NOT_FOUND): Data not found line %d.: This is a "normal" error that tells you that what you are querying cannot be found or you are at the end of the cursor.