Why can't a bind linux service to the loop-back only?

I am writing a server application that will provide a service on an ephemeral port that I only want accessible on the loopback interface. In order to do this, I am writing code like the following:

struct sockaddr_in bind_addr;

memset(&bind_addr,0,si开发者_运维问答zeof(bind_addr));
bind_addr.sin_family = AF_INET;
bind_addr.sin_port = 0;
bind_addr.sin_addr.s_addr = htonl(inet_addr("127.0.0.1"));
rcd = ::bind(
   socket_handle,
   reinterpret_cast<struct sockaddr *>(&bind_addr),
   sizeof(bind_addr));

The return value for this call to bind() is -1 and the value of errno is 99 (Cannot assign requested address). Is this failing because inet_addr() already returns its result in network order or is there some other reason?

inet_addr should be avoided, for there is a much saner method of constructing struct sockaddrs (which means it also obsoletes gethostby*):

#include <netdb.h>

/* Error checking omitted for brevity */
struct addrinfo hints = {.ai_flags = AI_PASSIVE};
struct addrinfo *res;
getaddrinfo("::1", NULL, &hints, &res); /* or 127.0.0.1 if you are 60+ */
bind(fd, res->ai_addr, res->ai_addrlen);
freeaddrinfo(res);

Is this failing because inet_addr() already returns its result in network order

Yes.

So remove the htonl call.