so-ecs@stekt1.oulu.fi (Juha Ruotsalainen ti) (04/23/91)
How can my program read a file bigger than 64k into memory. At the moment I try to read 64k`s at a time and the rest of it (less than 64k) afterwards. But after I`ve read 0xffff bytes, the next DosRead reads only 1 byte. Is there a problem with DosAllocHuge, I mean, shouldn`t it allocate a memory block larger than 64k. I have traced the DosRead call with CodeView, and was surprised to see that when the program tried to point past 64k area (jimi[0x10000]) there was an I/O error. I hope you understand my I`m trying to say here. Please help... -ECS
ballard@cheddar.ucs.ubc.ca (Alan Ballard) (04/24/91)
In article <SO-ECS.91Apr23115117@stekt1.oulu.fi> so-ecs@stekt1.oulu.fi (Juha Ruotsalainen ti) writes: >How can my program read a file bigger than 64k into memory. > ... >Is there a problem with DosAllocHuge.... DosAllocHuge allocates a set of consecutive segment descriptors. With appropriate pointer operations, it is possible to treat the result as one big array. But underneath, it really is a set of separate 64K segments. DosRead etc. will never go beyond the end of the segment you pass in as a parameter... they have no way of knowing it is OK to go on and use the next segment descriptor. I don't think there is any way to make DosRead read a full 64K in one operation, so I guess it will take two reads for each segment. e.g., read 0xffff to the base of one segment, 1 byte to the end of the segment, then 0xffff to the base of the next. Probably an easier way would be to just read in a series of 32K chunks and bump the segment pointer every second time. Alan Ballard | Internet: ballard@ucs.ubc.ca University Computing Services | Bitnet: USERAB1@UBCMTSG University of British Columbia | Phone: 604-822-3074 Vancouver B.C. Canada V6R 1Z2 | Fax: 604-822-5116
gah@nntp-server.caltech.edu (Geln A. Herrmannsfeldt) (04/26/91)
I thought I saw that putting 0 in for the length gives 65536 bytes, but I can't right now find it in the book. The length parameter is short, so a number greater than 65536 could not be specified.
larrys@watson.ibm.com (Larry Salomon, Jr.) (04/30/91)
In <1991Apr26.092056.8951@nntp-server.caltech.edu>, gah@nntp-server.caltech.edu (Geln A. Herrmannsfeldt) writes: > >I thought I saw that putting 0 in for the length gives 65536 bytes, >but I can't right now find it in the book. That is for DosAllocSeg. DosRead does not support 65536 byte reads (it's in the docs). >The length parameter is short, so a number greater than 65536 could >not be specified. Cheers, Larry Salomon, Jr. (aka 'Q') LARRYS@YKTVMV.BITNET OS/2 Applications and Tools larrys@ibmman.watson.ibm.com IBM T.J. Watson Research Center larrys@eng.clemson.edu Yorktown Heights, NY Disclaimer: The statements and/or opinions stated above are strictly my own and do not reflect the views of my employer. Additionally, I have a reputation for being obnoxious, so don't take any personal attacks too seriously.
cadsi@ccad.uiowa.edu (CADSI) (05/01/91)
From article <SO-ECS.91Apr23115117@stekt1.oulu.fi>, by so-ecs@stekt1.oulu.fi (Juha Ruotsalainen ti): > How can my program read a file bigger than 64k into memory. At the > moment I try to read 64k`s at a time and the rest of it (less than > 64k) afterwards. But after I`ve read 0xffff bytes, the next DosRead > reads only 1 byte. Is there a problem with DosAllocHuge, I mean, > shouldn`t it allocate a memory block larger than 64k. I have traced > the DosRead call with CodeView, and was surprised to see that when the > program tried to point past 64k area (jimi[0x10000]) there was an I/O > error. I hope you understand my I`m trying to say here. Please help... > -ECS Is this a problem with the fact that read and write can only r/w 64K - 1 bytes at a time, noting the fact that the error status return (-1) from read and write represents 64K exactly??? |----------------------------------------------------------------------------| |Tom Hite | The views expressed by me | |Manager, Product development | are mine, not necessarily | |CADSI (Computer Aided Design Software Inc. | the views of CADSI. | |----------------------------------------------------------------------------|
ejp@bohra.cpg.oz.au (Esmond Pitt) (05/01/91)
In article <1991Apr30.200832.9352@ccad.uiowa.edu> cadsi@ccad.uiowa.edu (CADSI) writes: > From article <SO-ECS.91Apr23115117@stekt1.oulu.fi>, by so-ecs@stekt1.oulu.fi (Juha Ruotsalainen ti): >> How can my program read a file bigger than 64k into memory. At the >> moment I try to read 64k`s at a time and the rest of it (less than >> 64k) afterwards. But after I`ve read 0xffff bytes, the next DosRead >> reads only 1 byte. > > Is this a problem with the fact that read and write can only r/w > 64K - 1 bytes at a time, noting the fact that the error status > return (-1) from read and write represents 64K exactly??? You're talking about read(). Juha asked about DosRead(). Let's talk about DosRead(). It doesn't return -1 on error at all, and even if it did, -1 does not represent '64k exactly'. 64k is (65536 == 0x10000), not (65535 == 0xffff == 64k - 1). The answer to Juha's question is that DosRead() can only read 0xffff bytes at a time. This is 1 short of 64k. After the DosRead() of 0xffff, the 64k segment then has 1 byte left in it. The second DosRead() therefore reads 1 byte into it. DosRead() won't cross segment boundaries. Juha then has to increment the selector returned by his DosAllocHuge() to form an address for the beginning of the linearly next segment, into which he should do more DosRead() calls, and so on. How are you, Juha? -- Esmond Pitt, Computer Power Group ejp@bohra.cpg.oz
cadsi@ccad.uiowa.edu (CADSI) (05/02/91)
From article <1991May1.043104.29860@bohra.cpg.oz.au>, by ejp@bohra.cpg.oz.au (Esmond Pitt): > In article <1991Apr30.200832.9352@ccad.uiowa.edu> cadsi@ccad.uiowa.edu (CADSI) writes: >> From article <SO-ECS.91Apr23115117@stekt1.oulu.fi>, by so-ecs@stekt1.oulu.fi (Juha Ruotsalainen ti): >>> How can my program read a file bigger than 64k into memory. At the >>> moment I try to read 64k`s at a time and the rest of it (less than >>> 64k) afterwards. But after I`ve read 0xffff bytes, the next DosRead >>> reads only 1 byte. >> >> Is this a problem with the fact that read and write can only r/w >> 64K - 1 bytes at a time, noting the fact that the error status >> return (-1) from read and write represents 64K exactly??? > > You're talking about read(). Juha asked about DosRead(). Let's talk > about DosRead(). It doesn't return -1 on error at all, and even if it > did, -1 does not represent '64k exactly'. OOOOOOpps, quite right, I meant 64K-1, I typed things wrong here, don't read what I typed, read what I meant! > 64k is (65536 == 0x10000), not (65535 == 0xffff == 64k - 1). |----------------------------------------------------------------------------| |Tom Hite | The views expressed by me | |Manager, Product development | are mine, not necessarily | |CADSI (Computer Aided Design Software Inc. | the views of CADSI. | |----------------------------------------------------------------------------|