Access to SEVERAL files via Standard Handles
Posted: 27 Mar 2012 04:51
The present topic is based on this one; you should read that topic first.
SETFILEPOINTER.COM program allows to process the lines of a redirected input file in any order, allowing to create a rudimentary Relational Data Base. However, a Batch file is limited to manage just two files: STDIN for input (SET /P) operations, and STDOUT for output (ECHO, etc.) operations. We could made good use of SETFILEPOINTER program in a better way if we could access more than one input and output files in a Batch file. How to do that? In a relatively easy way: just connect the additional files to unused handles (3-9) and use the appropiate handle in the input (SET /P <&#) or output (ECHO >&#) commands.
The Batch file below merge the lines of 3 input files into one output file with larger lines:The same method may be used to generate several output files.
NOTE: For some reason SETFILEPOINTER.COM program can NOT move the file pointer of handles 3-9. This means that, although handles 3-9 may be used to sequentially access several input/output files, only handles 0, 1 and 2 can be used for random access. If a program requires more than these 3 random access files, the workaround is simple although cumbersome: each I/O operation in a file with random access must be enclosed in this block: redirect the file to a standard handle: 0 for input, 1 for output; move its file pointer; read/write the desired record. This way, an unlimited number of random access files may be managed in a Batch file.
Below there is a complete example based on (a few) NBA players: the Data Base is comprised of a base data file (NBA-Players) and 2 related data files: Team and College (the Team file have also the Conference field), and several index files: byNumber, byName and byTeam. NBA-Players.txt file contains in each line (record) a NBA player Number, Name and Position fields, and the starting position of the lines where Team and College fields are stored in its corresponding files, separated by arrobas:The following Batch file (report.bat) display a report of the NBA-Players.txt file in the order given by the first parameter index file. In this case, the relation of the base file and all its related files is hard-coded in the program, but a general DataBase.bat program may be written with the aid of a scheme auxiliary file that describe these relations.This way, you may execute this command:... with these results:or this command:... with these results:
Antonio
SETFILEPOINTER.COM program allows to process the lines of a redirected input file in any order, allowing to create a rudimentary Relational Data Base. However, a Batch file is limited to manage just two files: STDIN for input (SET /P) operations, and STDOUT for output (ECHO, etc.) operations. We could made good use of SETFILEPOINTER program in a better way if we could access more than one input and output files in a Batch file. How to do that? In a relatively easy way: just connect the additional files to unused handles (3-9) and use the appropiate handle in the input (SET /P <&#) or output (ECHO >&#) commands.
The Batch file below merge the lines of 3 input files into one output file with larger lines:
Code: Select all
@echo off
setlocal EnableDelayedExpansion
3<input2.txt 4<input3.txt (
for /F "delims=" %%a in (input1.txt) do (
set line=
rem Read from input2.txt (and write line from input1 to output.txt):
set /P line=%%a <&3
rem Read from input3.txt (and write line from input2 to output.txt):
set /P line=!line! <&4
rem Write line from input3 to output.txt:
echo(!line!
)
) >output.txt
NOTE: For some reason SETFILEPOINTER.COM program can NOT move the file pointer of handles 3-9. This means that, although handles 3-9 may be used to sequentially access several input/output files, only handles 0, 1 and 2 can be used for random access. If a program requires more than these 3 random access files, the workaround is simple although cumbersome: each I/O operation in a file with random access must be enclosed in this block: redirect the file to a standard handle: 0 for input, 1 for output; move its file pointer; read/write the desired record. This way, an unlimited number of random access files may be managed in a Batch file.
Below there is a complete example based on (a few) NBA players: the Data Base is comprised of a base data file (NBA-Players) and 2 related data files: Team and College (the Team file have also the Conference field), and several index files: byNumber, byName and byTeam. NBA-Players.txt file contains in each line (record) a NBA player Number, Name and Position fields, and the starting position of the lines where Team and College fields are stored in its corresponding files, separated by arrobas:
NBA-Players.txt wrote: 20@Ray Allen @Guard @0 @0
30@Reggie Evans @Forward@30@14
9@Andre Iguodala@Forward@60@28
7@Lamar Odom @Forward@90@42
19@Beno Udrih @Guard @120@56
Team.txt wrote: Boston Celtics @Eastern
Los Angeles Clippers@Western
Philadelphia 76ers @Eastern
Dallas Mavericks @Western
Milwaukee Bucks @Eastern
The index files: byNumber.dex, byName.dex and byTeam.dex, just contain the appropiate order of NBA-Players.txt records:College.txt wrote: Connecticut
Iowa
Arizona
Rhode Island
Sempeter
Code: Select all
byNumber.ndx: byName.ndx: byTeam.ndx:
98 0 0
65 32 98
131 65 32
0 98 131
32 131 65
Code: Select all
@echo off
setlocal EnableDelayedExpansion
cls
echo Report of NBA Players %1
echo/
echo NUM. NAME POSITION TEAM CONFEREN. COLLEGE
echo/
for /F %%m in (%1.ndx) do (
<NBA-Players.txt (
SetFilePointer 0 %%m
set /P mainRecord=
)
for /F "tokens=1-5 delims=@" %%a in ("!mainRecord!") do (
<Team.txt (
SetFilePointer 0 %%d
set /P "team=%%a %%b %%c "
)
for /F "tokens=1,2 delims=@" %%x in ("!team!") do (
set team=%%x
set conference=%%y
)
<College.txt (
SetFilePointer 0 %%e
set /P "college=!team! !conference! "
)
echo !college!
)
)
echo/
Code: Select all
report byNameCode: Select all
Report of NBA Players byName
NUM. NAME POSITION TEAM CONFEREN. COLLEGE
20 Ray Allen Guard Boston Celtics Eastern Connecticut
30 Reggie Evans Forward Los Angeles Clippers Western Iowa
9 Andre Iguodala Forward Philadelphia 76ers Eastern Arizona
7 Lamar Odom Forward Dallas Mavericks Western Rhode Island
19 Beno Udrih Guard Milwaukee Bucks Eastern SempeterCode: Select all
report byTeamCode: Select all
Report of NBA Players byTeam
NUM. NAME POSITION TEAM CONFEREN. COLLEGE
20 Ray Allen Guard Boston Celtics Eastern Connecticut
7 Lamar Odom Forward Dallas Mavericks Western Rhode Island
30 Reggie Evans Forward Los Angeles Clippers Western Iowa
19 Beno Udrih Guard Milwaukee Bucks Eastern Sempeter
9 Andre Iguodala Forward Philadelphia 76ers Eastern Arizona
