<tt>char sun_path[]</tt> Socket pathname.

<tt>char sun_path[size]</tt> Socket pathname storage.

The sun_path member shall be the last member of the sockaddr_un structure, where size shall be an implementation-provided constant size of at least 92 bytes. This size value need not be accessible as a constant available for use in the application namespace.

The size of sun_path has intentionally been left undefined. This is because different implementations use different sizes. For example, 4.3 BSD uses a size of 108, and 4.4 BSD uses a size of 104. Since most implementations originate from BSD versions, the size is typically in the range 92 to 108.

The size of sun_path is required to be constant, but intentionally does not have a specified name for that constant. Historically, different implementations used different sizes. For example, 4.3 BSD used a size of 108, and 4.4 BSD used a size of 104. Since most implementations originate from BSD versions, the size is typically in the range 92 to 108. An application can deduce the size by using <tt>sizeof(((struct sockaddr_un *)0)->sun_path)</tt>.

Some implementations expose a macro <tt>SUN_LEN</tt> for the size of a pathname stored in <tt>sun_path</tt>. However, this was not widely adopted, and differences on how a terminating NUL byte is interpreted between implementations did not make it worth standardizing.

For AF_UNIX sockets, it is recommended that address points to a buffer of length greater than <tt>sizeof(struct sockaddr_un)</tt> which has been initialized with null bytes. That way, even if the implementation supports the use of all bytes of sun_path without a terminating null byte, the larger buffer guarantees that the sun_path member can then be passed to other interfaces that expect a null-terminated string. If no truncation occurred based on the input value of address_len, It is unspecified whether the returned address_len will be <tt>sizeof(struct sockaddr_un)</tt>, or merely a value at least as large as <tt>offsetof(struct sockaddr_un, sun_path)</tt> plus the number of non-null bytes stored in sun_path.

If the address family of the socket is AF_UNIX and the pathname in address names an existing file, including a symbolic link, bind() shall treat the address as already in use; see ERRORS below.

If the address family of the socket is AF_UNIX, the application shall ensure that a null terminator after the pathname is included in the sun_path member of address as a sockaddr_un structure, and that address_len is at least <tt>offsetof(struct sockaddr_un, sun_path) + 1</tt> plus the length of the pathname. If the pathname in the sun_path member of address names an existing file, including a symbolic link, bind( ) shall treat the address as already in use; see ERRORS below.

For AF_UNIX sockets, some implementations support an extension where address_len does not have to include a null terminator for the pathname stored in sun_path, which in turn allows a pathname to be one byte longer. However, such usage is not portable, and carries a risk of accessing beyond the intended bounds of the pathname length.

If the address family of the socket is AF_UNIX, the application shall ensure that a null terminator after the pathname is included in the sun_path member of address as a sockaddr_un structure, and that address_len is at least <tt>offsetof(struct sockaddr_un, sun_path) + 1</tt> plus the length of the pathname.

If the address family of the socket is AF_UNIX, the application shall ensure that a null terminator after the pathname is included in the sun_path member of dest_addr as a sockaddr_un structure, and that dest_len is at least <tt>offsetof(struct sockaddr_un, sun_path) + 1</tt> plus the length of the pathname.

For AF_UNIX sockets, some implementations support an extension where dest_len does not have to include a null terminator for the pathname stored in sun_path, which in turn allows a pathname to be one byte longer. However, such usage is not portable, and carries a risk of accessing beyond the intended bounds of the pathname length.