How do I use setsockopt(SO_REUSEADDR)?

by

Set the option after the socket has been successfully initialized. So, after:

sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) 
    error("ERROR opening socket");

You can add (with standard C99 compound literal support):

if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
    error("setsockopt(SO_REUSEADDR) failed");

Or:

const int enable = 1;
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int)) < 0)
    error("setsockopt(SO_REUSEADDR) failed");

Note than in addition to SO_REUSEADDR, you might need to set SO_REUSEPORT to get the desired behavior. This is done exactly the same way for both options.

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