|Syntax||error = READ_HEADER(#channel, buffer)|
The file that is opened on the given channel has its header data read into memory starting at the given address (buffer). The buffer address must have been reserved using RESERVE_HEAP, or some similar command.
The buffer must be at least 64 bytes long or unpredictable results will occur. The function will read the header but any memory beyond the end of the buffer will be overwritten if the buffer is too short. After a successful call to this function, the contents of the buffer will be as follows :
|Buffer + 0||File length||4 bytes long (see FILE_LENGTH)|
|Buffer + 4||File access||1 byte long - currently zero|
|Buffer + 5||File type||1 byte long (see FILE_TYPE)|
|Buffer + 6||File dataspace||4 bytes long (see FILE_DATASPACE)|
|Buffer + 10||Unused||4 bytes long|
|Buffer + 14||Name length||2 bytes long, size of filename|
|Buffer + 16||Filename||36 bytes long|
Directory devices also have the following additional data :
|Buffer + 52||Update date||4 bytes long (see FILE_UPDATE)|
|Buffer + 56||Reference date||4 bytes long - see below|
|Buffer + 60||Backup date||4 bytes long (see FILE_BACKUP)|
Miracle Systems hard disc’s users and level 2 users will find the files version number stored as the the 2 bytes starting at buffer + 56, the remaining 2 bytes of the reference date seem to be hex 094A or decimal 2378 which has no apparent meaning, this of course may change at some point!
This function returns an error code if something went wrong while attempting to read the file header or zero if everything went ok. It can be used as a more efficient method of finding out the details for a particular file rather than calling all the various FILE_XXX functions. Each of these functions internally call the READ_HEADER routine.
The filename can be extracted from the buffer by something like:
f$ = PEEK_STRING(buffer + 16, PEEK_W(buffer + 14)).
EXAMPLE The following example allows you to change the current dataspace requirements for an EXECutable file:
6445 DEFine PROCedure ALTER_DATASPACE 6450 LOCal base, loop, f$, ft, nv 6455 base = RESERVE_HEAP (64) 6460 IF base < 0 THEN 6465 PRINT "ERROR: " & base & ", reserving heap space." 6470 RETurn 6475 END IF 6480 REPeat loop 6485 INPUT'Enter filename:';f$ 6490 IF f$ = '' THEN EXIT loop 6495 ft = FILE_TYPE(f$) 6500 IF ft < 0 THEN 6465 PRINT "ERROR: " & ft & ", reading file type for " & f$ & "." 6510 END IF 6515 IF ft <> 1 THEN 6520 PRINT f$ & 'is not an executable file!' 6525 NEXT loop 6530 END IF 6535 PRINT 'Current dataspace is:'; FILE_DATASPACE(f$) 6540 INPUT 'Enter new value:'; nv 6545 OPEN #3,f$ : fer = READ_HEADER (#3,base) 6550 IF fer < 0 : CLOSE #3 : PRINT "READ_HEADER error: " & fer : NEXT loop 6555 POKE_L base + 6,nv 6560 fer = SET_HEADER(#3,base) 6565 IF fer < 0 : PRINT "SET_HEADER error: " & fer 6570 CLOSE #3 6575 END REPeat loop 6580 RELEASE_HEAP base 6585 END DEFine ALTER_DATASPACE