Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations strongm on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!
Memo File
- Thread starter Atlas
- Start date
darrellblackhawk
Programmer
To all: Sorry in advance for the long post.
To Atlas:
Fortunately, you get the chance to write some bullet-proof code.
Seriously explore the data table/memo structures and build your own correction program. (see below)
I use a posting engine in the background to protect against memo corruption and I've even included it into my project manager to catche file corruption on the fly.
Although I have to admit I still get bit every now and again. :-0
I've included the table struct from MSDN
Good luck!
Table File Structure (.dbc, .dbf, .frx, .lbx, .mnx, .pjx, .scx, .vcx)
See Also
Visual FoxPro uses tables to store data that defines different file types. The file types that are saved as table files are:
Table (.dbf)
Database (.dbc)
Form (.scx)
Label (.lbx)
Menu (.mnx)
Project (.pjx)
Report (.frx)
Visual Class Library (.vcx)
Because these files are actually tables, you can use and browse them in the same way that you browse any .dbf file.
A table file is made up of a header record and data records. The header record defines the structure of the table and contains any other information related to the table. It starts at file position zero. The data records1 follow the header (in consecutive bytes) and contain the actual text of the fields.
For information about the table structures of the different file types, see Table Structures of Table Files.
The length of a record (in bytes) is determined by summing the defined lengths of all fields. Integers in table files are stored with the least significant byte first.
Table Header Record Structure
Byte offset Description
0 Type of file
0x02FoxBASE
0x03FoxBASE+/dBASE III PLUS, no memo
0x30Visual FoxPro
0x43dBASE IV SQL table files, no memo
0x63dBASE IV SQL system files, no memo
0x83FoxBASE+/dBASE III PLUS, with memo
0x8BdBASE IV with memo
0xCBdBASE IV SQL table files, with memo
0xF5FoxPro 2.x (or earlier) with memo
0xFBFoxBASE
1 – 3 Last update (YYMMDD)
4 – 7 Number of records in file
8 – 9 Position of first data record
10 – 11 Length of one data record (including delete
flag)
12 – 27 Reserved
28 Table Flags
0x01file has a structural .cdx
0x02file has a Memo field
0x04file is a database (.dbc)
Note that this byte can contain the sum of
any of the above values. For example, 0x03
indicates the table has a structural .cdx
and a Memo field.
29 Code page mark
30 – 31 Reserved, contains 0x00
32 – n Field subrecords
The number of fields determines the number of
field subrecords. There is one field subrecord
for each field in the table.
n+1 Header record terminator (0x0D)
n+2 to n+264 A 263-byte range that contains the backlink
information (the relative path of an associated
database (.dbc)). If the first byte is 0x00
then the file is not associated with a
database. Hence, database files themselves
always contain 0x00.
1 The data in the data file starts at the position indicated in bytes 8 to 9 of the header record. Data records begin with a delete flag byte. If this byte is an ASCII space (0x20) the record is not deleted; if the first byte is an asterisk (0x2A) the record is deleted. The data from the fields named in the field subrecords follows the delete flag.
Field Subrecords Structure
Byte offset Description
0 – 10 Field name (maximum of 10 characters; if less than
10, it is padded with null character (0x00))
11 Field Type:
C–Character
Y–Currency
N–Numeric
F–Float
D–Date
T–DateTime
B–Double
I–Integer
L–Logical
M–Memo
G–General
C–Character (binary)
M–Memo (binary)
P–Picture
12 – 15 Displacement of field in record
16 Length of field (in bytes)
17 Number of decimal places
18 Field Flags
0x01 System Column (not visible to user)
0x02Column can store null values
0x04Binary column (for CHAR and MEMO only)
19 – 32 Reserved
For information about limitations on characters per record, maximum fields, and so on, see Visual FoxPro System Capacities.
Remarks
Visual FoxPro does not modify the header of a file that has been saved to a FoxPro 2.x file format unless one of the following features has been added to the file:
Null value support
DateTime, Currency, and Double data types
CHAR or MEMO field is marked as Binary
A table is added to a database (.dbc) file
Tip You can use the following formula to return the number of fields in a table file: (x – 296/32). In the formula, x is the position of the first record (bytes 8 to 9 in the table header record), 296 is 263 (backlink info) + 1 (header record terminator) + 32 (first field subrecord), and 32 is the length of a field subrecord.
To Atlas:
Fortunately, you get the chance to write some bullet-proof code.
Seriously explore the data table/memo structures and build your own correction program. (see below)
I use a posting engine in the background to protect against memo corruption and I've even included it into my project manager to catche file corruption on the fly.
Although I have to admit I still get bit every now and again. :-0
I've included the table struct from MSDN
Good luck!
Table File Structure (.dbc, .dbf, .frx, .lbx, .mnx, .pjx, .scx, .vcx)
See Also
Visual FoxPro uses tables to store data that defines different file types. The file types that are saved as table files are:
Table (.dbf)
Database (.dbc)
Form (.scx)
Label (.lbx)
Menu (.mnx)
Project (.pjx)
Report (.frx)
Visual Class Library (.vcx)
Because these files are actually tables, you can use and browse them in the same way that you browse any .dbf file.
A table file is made up of a header record and data records. The header record defines the structure of the table and contains any other information related to the table. It starts at file position zero. The data records1 follow the header (in consecutive bytes) and contain the actual text of the fields.
For information about the table structures of the different file types, see Table Structures of Table Files.
The length of a record (in bytes) is determined by summing the defined lengths of all fields. Integers in table files are stored with the least significant byte first.
Table Header Record Structure
Byte offset Description
0 Type of file
0x02FoxBASE
0x03FoxBASE+/dBASE III PLUS, no memo
0x30Visual FoxPro
0x43dBASE IV SQL table files, no memo
0x63dBASE IV SQL system files, no memo
0x83FoxBASE+/dBASE III PLUS, with memo
0x8BdBASE IV with memo
0xCBdBASE IV SQL table files, with memo
0xF5FoxPro 2.x (or earlier) with memo
0xFBFoxBASE
1 – 3 Last update (YYMMDD)
4 – 7 Number of records in file
8 – 9 Position of first data record
10 – 11 Length of one data record (including delete
flag)
12 – 27 Reserved
28 Table Flags
0x01file has a structural .cdx
0x02file has a Memo field
0x04file is a database (.dbc)
Note that this byte can contain the sum of
any of the above values. For example, 0x03
indicates the table has a structural .cdx
and a Memo field.
29 Code page mark
30 – 31 Reserved, contains 0x00
32 – n Field subrecords
The number of fields determines the number of
field subrecords. There is one field subrecord
for each field in the table.
n+1 Header record terminator (0x0D)
n+2 to n+264 A 263-byte range that contains the backlink
information (the relative path of an associated
database (.dbc)). If the first byte is 0x00
then the file is not associated with a
database. Hence, database files themselves
always contain 0x00.
1 The data in the data file starts at the position indicated in bytes 8 to 9 of the header record. Data records begin with a delete flag byte. If this byte is an ASCII space (0x20) the record is not deleted; if the first byte is an asterisk (0x2A) the record is deleted. The data from the fields named in the field subrecords follows the delete flag.
Field Subrecords Structure
Byte offset Description
0 – 10 Field name (maximum of 10 characters; if less than
10, it is padded with null character (0x00))
11 Field Type:
C–Character
Y–Currency
N–Numeric
F–Float
D–Date
T–DateTime
B–Double
I–Integer
L–Logical
M–Memo
G–General
C–Character (binary)
M–Memo (binary)
P–Picture
12 – 15 Displacement of field in record
16 Length of field (in bytes)
17 Number of decimal places
18 Field Flags
0x01 System Column (not visible to user)
0x02Column can store null values
0x04Binary column (for CHAR and MEMO only)
19 – 32 Reserved
For information about limitations on characters per record, maximum fields, and so on, see Visual FoxPro System Capacities.
Remarks
Visual FoxPro does not modify the header of a file that has been saved to a FoxPro 2.x file format unless one of the following features has been added to the file:
Null value support
DateTime, Currency, and Double data types
CHAR or MEMO field is marked as Binary
A table is added to a database (.dbc) file
Tip You can use the following formula to return the number of fields in a table file: (x – 296/32). In the formula, x is the position of the first record (bytes 8 to 9 in the table header record), 296 is 263 (backlink info) + 1 (header record terminator) + 32 (first field subrecord), and 32 is the length of a field subrecord.
- Status
Similar threads
- Locked
- Question
