shm_open

shm_open() creates or opens a POSIX shared memory object.

Prototype

#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>

int shm_open(const char *name, int oflag, mode_t mode);

Typical Usage

int fd = shm_open("/demo_shm", O_CREAT | O_RDWR, 0600);
if (fd < 0) {
    perror("shm_open");
    return -1;
}

Important Rules

• The name should start with /.
• Use ftruncate() to set the object size before mmap().
• Use shm_unlink() to remove the name when cleanup is required.

Return Value

• file descriptor on success
• -1 on error, with errno set

Common Pitfalls

Warning

shm_open() creates a memory object, but it does not map it. Use mmap() after setting the size.

Related Topics

• POSIX Shared Memory
• mmap