How To Use ecpg

PostgreSQL 7.2 Documentation
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# 6.3. How To Use ecpg

This section describes how to use ecpg.

## 6.3.1. Preprocessor

The preprocessor is called ecpg. After installation it resides in the PostgreSQL `bin/` directory.

## 6.3.2. Library

The ecpg library is called `libecpg.a` or `libecpg.so`. Additionally, the library uses the `libpq` library for communication to the PostgreSQL server. You will have to link your program using `-lecpg -lpq`.

The library has some methods that are "hidden" but may prove useful.

- `ECPGdebug(int `on`, FILE *`stream`)` turns on debug logging if called with the first argument non-zero. Debug logging is done on `stream`. Most SQL statement log their arguments and results.

  The most important function , `ECPGdo`, logs all SQL statements with both the expanded string, i.e. the string with all the input variables inserted, and the result from the PostgreSQL server. This can be very useful when searching for errors in your SQL statements.

- `ECPGstatus()` This method returns TRUE if we are connected to a database and FALSE if not.

## 6.3.3. Error handling

To detect errors from the PostgreSQL server, include a line like:

    exec sql include sqlca;

in the include section of your file. This will define 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;

If an 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 PostgreSQL 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 PostgreSQL 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.`

  PostgreSQL returned `PGRES_EMPTY_QUERY`, probably because the query indeed was empty.

`-209 (ECPG_MISSING_INDICATOR): NULL value without indicator in line %d.`

  PostgreSQL returned `ECPG_MISSING_INDICATOR` because a NULL was returned and no NULL indicator variable was supplied.

`-210 (ECPG_NO_ARRAY): Variable is not an array in line %d.`

  PostgreSQL returned `ECPG_NO_ARRAY` because 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.`

  PostgreSQL returned `ECPG_DATA_NOT_ARRAY` because 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.

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