> So if the question is why do you need to include ftruncate() in the code,
> take a look here:
No, that was not the question. W/o ftruncate(), _referencing_ the memory
becomes a problem (and the original code did not do that, but simply mmap'ed
two files).
> > Adding the <unistd.h> fixes the problem in all its iterations
OP privately wrote:
> The problem is also fixed by correct type-casting in the calls to mmap() ...
>
> mmap1 = mmap(NULL, (size_t) 524304, PROT_WRITE | PROT_READ, MAP_SHARED,
> shm_fd1, 0);
>
> The address returned from the call to mmap() -- with or without the
> ftruncate() -- was bad without the (size_t) specification.
(note "with or without ftruncate()")
And I ask again (last time, I promise), how on Earth adding <unistd.h> to
the code below would make the code suddenly working? (Like I said before,
that code worked for me, with -Wall showing nothing, from the very beginning.)
Anton Lavrentiev
Contractor NIH/NLM/NCBI
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/errno.h>
#include <fcntl.h>
#include <sys/mman.h>
int main()
{
int shm_fd1, shm_fd2;
char *mmap1, *mmap2;
/* get fd for each block of memory */
shm_fd1 = shm_open("/block1", O_CREAT | O_RDWR, 0666);
if (shm_fd1 == -1) {
fprintf(stderr, "Couldn't get fd for block1 (%s)\n",
strerror(errno));
exit(1);
}
shm_fd2 = shm_open("/block2", O_CREAT | O_RDWR, 0666);
if (shm_fd2 == -1) {
fprintf(stderr, "Couldn't get fd for /UNI_queue (%s)\n",
strerror(errno));
exit(1);
}
/* map each block */
mmap1 = mmap(NULL, 524304, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd1,
0);
if (mmap1 == (char *)-1) {
fprintf(stderr, "Couldn't map memory for /block1 (%s)\n",
strerror(errno));
exit(1);
}
mmap2 = mmap(NULL, 524304, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd2,
0);
if (mmap2 == (char *)-1) {
fprintf(stderr, "Couldn't map memory for /block2 (%s)\n",
strerror(errno));
exit(1);
}
fprintf(stdout, "Shared memory initialized\n");
exit(0);
}
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