Re: [Mingw-w64-public] Short read mystery
On 10/16/13, Edscott Wilson edscott.wilson.gar...@gmail.com wrote:
I've been banging my head against the monitor for the past nine hours and
narrowed a problem down to the following.
I've found that for certain data, the read() function will return a short
byte count.
Take the following test file: http://xffm.org/test.dbh and compile and
execute the following program:
#include stdio.h
#include stdlib.h
#include sys/types.h
#include sys/stat.h
#include fcntl.h
#include errno.h
int main(int argc, char **argv){
int fd = open(test.dbh,O_RDWR);
Try adding O_BINARY to the open() flags here.
void *data = malloc(256);
size_t bytes = read(fd, data, 256);
printf(bytes read=%ld\n, (long)bytes);
printf(errno=%s\n, strerror(errno));
close(fd);
FILE *f = fopen(test.dbh, r);
bytes = fread(data, 1, 256, f);
printf(bytes fread=%ld\n, (long)bytes);
return 1;
}
This is the output of the above program compiled with mingw gcc:
bytes read=255
errno=No error
bytes fread=256
Which is wrong. I get the same broken result with both:
gcc.exe (rev5, Built by MinGW-W64 project) 4.8.1
and
gcc.exe (GCC) 4.6.2 (from mingw-32)
Linux, of course, reads the 256 bytes correctly.
So there is something in the file which breaks the read on Windows.
What could possibly be wrong?
Is there some Windows trick you need apply to make read() work as it is
intended?
Or would it be a bug of the mingw gcc port?
Any help is appreciated.
--
O.S.
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Re: [Mingw-w64-public] Short read mystery
Edscott Wilson писал 2013-10-16 03:07:
I've been banging my head against the monitor for the past nine hours and
narrowed a problem down to the following.
I've found that for certain data, the read() function will return a short
byte count.
Take the following test file: http://xffm.org/test.dbh [1] and compile and
execute the following program:
#include stdio.h
#include stdlib.h
#include sys/types.h
#include sys/stat.h
#include fcntl.h
#include errno.h
int main(int argc, char **argv){
int fd = open(test.dbh,O_RDWR);
void *data = malloc(256);
size_t bytes = read(fd, data, 256);
printf(bytes read=%ldn, (long)bytes);
printf(errno=%sn, strerror(errno));
close(fd);
FILE *f = fopen(test.dbh, r);
Maybe:
FILE *f = fopen(test.dbh, rb);
?
--
Regards, niXman
___
Dual-target(32 64-bit) MinGW compilers for 32 and 64-bit Windows:
http://sourceforge.net/projects/mingw-w64/
___
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Links:
--
[1] http://xffm.org/test.dbh
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Re: [Mingw-w64-public] Short read mystery
Greetings Edscott Wilson,
In Unix, \r\n for a newline, versus '\n' in Windows?
Maybe a unix2dos the file would put everything in
perspective?
Edscott Wilson wrote:
I've been banging my head against the monitor for the past
nine hours and
narrowed a problem down to the following.
I've found that for certain data, the read() function will
return a short
byte count.
Take the following test file: http://xffm.org/test.dbh and
compile and
execute the following program:
#include stdio.h
#include stdlib.h
#include sys/types.h
#include sys/stat.h
#include fcntl.h
#include errno.h
int main(int argc, char **argv){
int fd = open(test.dbh,O_RDWR);
void *data = malloc(256);
size_t bytes = read(fd, data, 256);
printf(bytes read=%ld\n, (long)bytes);
printf(errno=%s\n, strerror(errno));
close(fd);
FILE *f = fopen(test.dbh, r);
bytes = fread(data, 1, 256, f);
printf(bytes fread=%ld\n, (long)bytes);
return 1;
}
This is the output of the above program compiled with mingw
gcc:
bytes read=255
errno=No error
bytes fread=256
Which is wrong. I get the same broken result with both:
gcc.exe (rev5, Built by MinGW-W64 project) 4.8.1
and
gcc.exe (GCC) 4.6.2 (from mingw-32)
Linux, of course, reads the 256 bytes correctly.
So there is something in the file which breaks the read on
Windows.
What could possibly be wrong?
Is there some Windows trick you need apply to make read()
work as it is
intended?
Or would it be a bug of the mingw gcc port?
Any help is appreciated.
--
October Webinars: Code for Performance
Free Intel webinars can help you accelerate application performance.
Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from
the latest Intel processors and coprocessors. See abstracts and register
http://pubads.g.doubleclick.net/gampad/clk?id=60135031iu=/4140/ostg.clktrk
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