Re: How to lseek the larger file > 2GB under linux

[Michal Nazarewicz <mina86@tlen.pl>]

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Nicle <ynicle@gmail.com> writes:
> I have a file > 2GB, and my job is seeking the file to pos: 2.1G.
> But, it seems that the lseek64 doesn't work.

> #define _LARGEFILE64_SOURCE
> #include ...
>
> int main() {
>  int fd = -1;
>  long long pos = (long long) 2*1024*1024*1024 + 10; // over 2G

A long shot, but try (2LL << 30) (the "LL" is important).  I don't
expect that will make it work but if you're out of ideas... ;)

>  fd = open(FILENAME, O_WRONLY|O_LARGEFILE);
>  if (fd < 0) { /* ... */ }
>
>  if (lseek64(fd, pos, SEEK_SET) < 0)
>      fprintf(stderr, "Failed seeking to %lld, %s\n", pos, strerror(errno));
>
>  return 0;
> }

>  Then the building cmd:   gcc -o test test.c -D_FILE_OFFSET_BITS=64
>  Output:            >     Failed seeking to 2147483658, Success.
>
> The return val of lseek64  was "<0", but the strerror told me "Success".

BTW. The following works fine for me:

#v+
#define _LARGEFILE64_SOURCE

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#define RUN(expr) if ((expr) < 0) { perror(#expr); return 1; } else (void)0

int main(void) {
	const long long pos = (2LL << 30) + 10;
	int fd;

	RUN(fd = open("deleteme", O_WRONLY | O_LARGEFILE | O_CREAT, 0600));
	RUN(lseek64(fd, pos, SEEK_SET));
	RUN(write(fd, "a", 1));
	return 0;
}
#v-

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 .o. | Liege of Serenly Enlightened Majesty of      o' \,=./ `o
 ..o | Computer Science,  Michal "mina86" Nazarewicz   (o o)
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