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Home > Archive > Unix Programming > October 2005 > FILE* and fd
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| vineeth 2005-10-24, 3:48 pm |
| hi all,
Is there any advantage in using FILE* related api calls instead of
using the file descriptor and related calls like read()?
pls share your ideas.
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| Gordon Burditt 2005-10-24, 3:48 pm |
| >Is there any advantage in using FILE* related api calls instead of
>using the file descriptor and related calls like read()?
>pls share your ideas.
The use of, say, getc() and putc() calls or other
single-character-at-a-time I/O operations using stdio can be
significantly faster than single-character read() or write() calls.
If you're doing I/O in large blocks anyway, reading and writing in
64k read() or write() calls might be faster than stdio calls (which
might use a buffer like 512 bytes or 4k or 16k).
This can interact with the sector interleave of floppies and hard
disks to the point that writing a whole floppy as a buffered device
can take 1 minute with stdio and over an hour with
single-character-at-a-time write() calls.
Gordon L. Burditt
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| Keith Thompson 2005-10-24, 3:48 pm |
| "vineeth" <nvineeth@gmail.com> writes:
> Is there any advantage in using FILE* related api calls instead of
> using the file descriptor and related calls like read()?
> pls share your ideas.
The FILE* calls are defined by the C language standard. The calls
using file descriptors are not; they're defined by the POSIX standard.
Code using Unix-style file descriptors is less portable than code that
uses only the standard FILE* interface.
(This may not be relevant if you don't care about portability to
non-Unix system.)
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
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| 50295@web.de 2005-10-28, 4:53 pm |
|
Keith Thompson wrote:
> "vineeth" <nvineeth@gmail.com> writes:
>
> The FILE* calls are defined by the C language standard. The calls
> using file descriptors are not; they're defined by the POSIX standard.
> Code using Unix-style file descriptors is less portable than code that
> uses only the standard FILE* interface.
>
> (This may not be relevant if you don't care about portability to
> non-Unix system.)
Just a note, the file decriptor is a member of the FILE structure. i.e:
typedef struct {
unsigned char *curp; /* Current active pointer (mandatory) */
unsigned char *buffer; /* Data transfer buffer (mandatory) */
int level; /* fill/empty level of buffer */
int bsize; /* Buffer size (mandatory) */
unsigned short istemp; /* Temporary file indicator */
unsigned short flags; /* File status flags (mandatory) */
wchar_t hold; /* ungetc char if no buffer exists */
char fd; /* FILE DESCRIPTOR (mandatory) */
unsigned char token; /* Used for validity checking */
} FILE; /* This is the FILE type
Even the MSDN has its versions of read(2) and write(2) -- using file
descriptors. See:
_write() : http://tinyurl.com/ddon8
_read() : http://tinyurl.com/9ju9e
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| Lew Pitcher 2005-10-28, 4:53 pm |
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50295@web.de wrote:
> Keith Thompson wrote:
>
>
>
> Just a note, the file decriptor is a member of the FILE structure. i.e:
on the platform you got that from.
I can promise you that the FILE structure is not the same on all platforms
> Even the MSDN has its versions of read(2) and write(2) -- using file
> descriptors.
/But/, systems like Z/OS (OS/390, MVS, etc.) /do not/ have file descriptors.
- --
Lew Pitcher
IT Specialist, Enterprise Data Systems,
Enterprise Technology Solutions, TD Bank Financial Group
(Opinions expressed are my own, not my employers')
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