socketgetservbyname

The socketgetservbyname function is a standard library routine found in many operating systems' networking APIs, particularly POSIX-compliant systems. Its primary purpose is to translate a service name, such as "http" or "ftp," into a port number. This is a crucial step in establishing network connections.

When a program wants to connect to a specific service on a remote host, it typically needs to know the port number associated with that service. Instead of hardcoding these numbers, which can be prone to errors and difficult to manage, applications use socketgetservbyname. The function queries the system's service database, often stored in files like /etc/services on Unix-like systems. This database maps well-known service names to their default port numbers and the transport protocol (TCP or UDP) they use.

The function typically takes two arguments: the service name as a string and optionally the protocol name (e.g., "tcp" or "udp"). It returns a pointer to a structure that contains the port number, protocol name, and aliases for the service. If the service name is not found in the database or an error occurs, the function returns NULL. This abstraction allows developers to write more portable and maintainable network code, as they don't need to worry about the specific port assignments for different services or operating systems.