dbfopen.c

Source code, and some other odds and ends can be downloaded from http://shapelib.maptools.org/dl.

	if( fseek( psDBF->fp, nRecordOffset, 0 ) != 0 )
        {
            fprintf( stderr, "fseek(%d) failed on DBF file.\n",
                     nRecordOffset );
            return NULL;
        }

	if( fread( psDBF->pszCurrentRecord, psDBF->nRecordLength, 
                   1, psDBF->fp ) != 1 )
        {
            fprintf( stderr, "fread(%d) failed on DBF file.\n",
                     psDBF->nRecordLength );
            return NULL;
        }

	psDBF->nCurrentRecord = hEntity;
    }

    pabyRec = (unsigned char *) psDBF->pszCurrentRecord;

/* -------------------------------------------------------------------- */
/*	Ensure our field buffer is large enough to hold this buffer.	*/
/* -------------------------------------------------------------------- */
    if( psDBF->panFieldSize[iField]+1 > nStringFieldLen )
    {
	nStringFieldLen = psDBF->panFieldSize[iField]*2 + 10;
	pszStringField = (char *) SfRealloc(pszStringField,nStringFieldLen);
    }

/* -------------------------------------------------------------------- */
/*	Extract the requested field.					*/
/* -------------------------------------------------------------------- */
    strncpy( pszStringField, 
	     ((const char *) pabyRec) + psDBF->panFieldOffset[iField],
	     psDBF->panFieldSize[iField] );
    pszStringField[psDBF->panFieldSize[iField]] = '\0';

    pReturnField = pszStringField;

/* -------------------------------------------------------------------- */
/*      Decode the field.                                               */
/* -------------------------------------------------------------------- */
    if( chReqType == 'N' )
    {
        dDoubleField = atof(pszStringField);

	pReturnField = &dDoubleField;
    }

/* -------------------------------------------------------------------- */
/*      Should we trim white space off the string attribute value?      */
/* -------------------------------------------------------------------- */
#ifdef TRIM_DBF_WHITESPACE
    else
    {
        char	*pchSrc, *pchDst;

        pchDst = pchSrc = pszStringField;
        while( *pchSrc == ' ' )
            pchSrc++;

        while( *pchSrc != '\0' )
            *(pchDst++) = *(pchSrc++);
        *pchDst = '\0';

        while( pchDst != pszStringField && *(--pchDst) == ' ' )
            *pchDst = '\0';
    }
#endif
    
    return( pReturnField );
}

/************************************************************************/
/*                        DBFReadIntAttribute()                         */
/*                                                                      */
/*      Read an integer attribute.                                      */
/************************************************************************/

int SHPAPI_CALL
DBFReadIntegerAttribute( DBFHandle psDBF, int iRecord, int iField )

{
    double	*pdValue;

    pdValue = (double *) DBFReadAttribute( psDBF, iRecord, iField, 'N' );

    if( pdValue == NULL )
        return 0;
    else
        return( (int) *pdValue );
}

/************************************************************************/
/*                        DBFReadDoubleAttribute()                      */
/*                                                                      */
/*      Read a double attribute.                                        */
/************************************************************************/

double SHPAPI_CALL
DBFReadDoubleAttribute( DBFHandle psDBF, int iRecord, int iField )

{
    double	*pdValue;

    pdValue = (double *) DBFReadAttribute( psDBF, iRecord, iField, 'N' );

    if( pdValue == NULL )
        return 0.0;
    else
        return( *pdValue );
}

/************************************************************************/
/*                        DBFReadStringAttribute()                      */
/*                                                                      */
/*      Read a string attribute.                                        */
/************************************************************************/

const char SHPAPI_CALL1(*)
DBFReadStringAttribute( DBFHandle psDBF, int iRecord, int iField )

{
    return( (const char *) DBFReadAttribute( psDBF, iRecord, iField, 'C' ) );
}

/************************************************************************/
/*                         DBFIsAttributeNULL()                         */
/*                                                                      */
/*      Return TRUE if value for field is NULL.                         */
/*                                                                      */
/*      Contributed by Jim Matthews.                                    */
/************************************************************************/

int SHPAPI_CALL
DBFIsAttributeNULL( DBFHandle psDBF, int iRecord, int iField )

{
    const char	*pszValue;

    pszValue = DBFReadStringAttribute( psDBF, iRecord, iField );

    switch(psDBF->pachFieldType[iField])
    {
      case 'N':
      case 'F':
        /* NULL numeric fields have value "****************" */
        return pszValue[0] == '*';

      case 'D':
        /* NULL date fields have value "00000000" */
        return strncmp(pszValue,"00000000",8) == 0;

      case 'L':
        /* NULL boolean fields have value "?" */ 
        return pszValue[0] == '?';

      default:
        /* empty string fields are considered NULL */
        return strlen(pszValue) == 0;
    }
    return FALSE;
}

/************************************************************************/
/*                          DBFGetFieldCount()                          */
/*                                                                      */
/*      Return the number of fields in this table.                      */
/************************************************************************/

int SHPAPI_CALL
DBFGetFieldCount( DBFHandle psDBF )

{
    return( psDBF->nFields );
}

/************************************************************************/
/*                         DBFGetRecordCount()                          */
/*                                                                      */
/*      Return the number of records in this table.                     */
/************************************************************************/

int SHPAPI_CALL
DBFGetRecordCount( DBFHandle psDBF )

{
    return( psDBF->nRecords );
}

/************************************************************************/
/*                          DBFGetFieldInfo()                           */
/*                                                                      */
/*      Return any requested information about the field.               */
/************************************************************************/

DBFFieldType SHPAPI_CALL
DBFGetFieldInfo( DBFHandle psDBF, int iField, char * pszFieldName,
                 int * pnWidth, int * pnDecimals )

{
    if( iField < 0 || iField >= psDBF->nFields )
        return( FTInvalid );

    if( pnWidth != NULL )
        *pnWidth = psDBF->panFieldSize[iField];

    if( pnDecimals != NULL )
        *pnDecimals = psDBF->panFieldDecimals[iField];

    if( pszFieldName != NULL )
    {
	int	i;

	strncpy( pszFieldName, (char *) psDBF->pszHeader+iField*32, 11 );
	pszFieldName[11] = '\0';
	for( i = 10; i > 0 && pszFieldName[i] == ' '; i-- )
	    pszFieldName[i] = '\0';
    }

    if( psDBF->pachFieldType[iField] == 'N' 
        || psDBF->pachFieldType[iField] == 'F'
        || psDBF->pachFieldType[iField] == 'D' )
    {
	if( psDBF->panFieldDecimals[iField] > 0 )
	    return( FTDouble );
	else
	    return( FTInteger );
    }
    else
    {
	return( FTString );
    }
}

/************************************************************************/
/*                         DBFWriteAttribute()                          */
/*									*/
/*	Write an attribute record to the file.				*/
/************************************************************************/

static int DBFWriteAttribute(DBFHandle psDBF, int hEntity, int iField,
			     void * pValue )

{
    int	       	nRecordOffset, i, j;
    unsigned char	*pabyRec;
    char	szSField[400], szFormat[20];

/* -------------------------------------------------------------------- */
/*	Is this a valid record?						*/
/* -------------------------------------------------------------------- */
    if( hEntity < 0 || hEntity > psDBF->nRecords )
        return( FALSE );

    if( psDBF->bNoHeader )
        DBFWriteHeader(psDBF);

/* -------------------------------------------------------------------- */
/*      Is this a brand new record?                                     */
/* -------------------------------------------------------------------- */
    if( hEntity == psDBF->nRecords )
    {
	DBFFlushRecord( psDBF );

	psDBF->nRecords++;
	for( i = 0; i < psDBF->nRecordLength; i++ )
	    psDBF->pszCurrentRecord[i] = ' ';

	psDBF->nCurrentRecord = hEntity;
    }

/* -------------------------------------------------------------------- */
/*      Is this an existing record, but different than the last one     */
/*      we accessed?                                                    */
/* -------------------------------------------------------------------- */
    if( psDBF->nCurrentRecord != hEntity )
    {
	DBFFlushRecord( psDBF );

	nRecordOffset = psDBF->nRecordLength * hEntity + psDBF->nHeaderLength;

	fseek( psDBF->fp, nRecordOffset, 0 );
	fread( psDBF->pszCurrentRecord, psDBF->nRecordLength, 1, psDBF->fp );

	psDBF->nCurrentRecord = hEntity;
    }

    pabyRec = (unsigned char *) psDBF->pszCurrentRecord;

    psDBF->bCurrentRecordModified = TRUE;
    psDBF->bUpdated = TRUE;

/* -------------------------------------------------------------------- */
/*      Translate NULL value to valid DBF file representation.          */
/*                                                                      */
/*      Contributed by Jim Matthews.                                    */
/* -------------------------------------------------------------------- */
    if( pValue == NULL )
    {
        switch(psDBF->pachFieldType[iField])
        {
          case 'N':
          case 'F':
	    /* NULL numeric fields have value "****************" */
            memset( (char *) (pabyRec+psDBF->panFieldOffset[iField]), '*', 
                    psDBF->panFieldSize[iField] );
            break;

          case 'D':
	    /* NULL date fields have value "00000000" */
            memset( (char *) (pabyRec+psDBF->panFieldOffset[iField]), '0', 
                    psDBF->panFieldSize[iField] );
            break;

          case 'L':
	    /* NULL boolean fields have value "?" */ 
            memset( (char *) (pabyRec+psDBF->panFieldOffset[iField]), '?', 
                    psDBF->panFieldSize[iField] );
            break;

          default:
            /* empty string fields are considered NULL */
            memset( (char *) (pabyRec+psDBF->panFieldOffset[iField]), '\0', 
                    psDBF->panFieldSize[iField] );
            break;
        }
        return TRUE;
    }