This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
#include <netdb.h> void endnetent(void); struct netent *getnetbyaddr(uint32_t net, int type); struct netent *getnetbyname(const char *name); struct netent *getnetent(void); void setnetent(int stayopen);
These functions shall retrieve information about networks. This information is considered to be stored in a database that can be accessed sequentially or randomly. The implementation of this database is unspecified.
The setnetent() function shall open and rewind the database. If the stayopen argument is non-zero, the connection to the net database shall not be closed after each call to getnetent() (either directly, or indirectly through one of the other getnet*() functions), and the implementation may maintain an open file descriptor to the database.
The getnetent() function shall read the next entry of the database, opening and closing a connection to the database as necessary.
The getnetbyaddr() function shall search the database from the beginning, and find the first entry for which the address family specified by type matches the n_addrtype member and the network number net matches the n_net member, opening and closing a connection to the database as necessary. The net argument shall be the network number in host byte order.
The getnetbyname() function shall search the database from the beginning and find the first entry for which the network name specified by name matches the n_name member, opening and closing a connection to the database as necessary.
The getnetbyaddr(), getnetbyname(), and getnetent() functions shall each return a pointer to a netent structure, the members of which shall contain the fields of an entry in the network database.
The endnetent() function shall close the database, releasing any open file descriptor.
These functions need not be thread-safe.
Upon successful completion, getnetbyaddr(), getnetbyname(), and getnetent() shall return a pointer to a netent structure if the requested entry was found, and a null pointer if the end of the database was reached or the requested entry was not found. Otherwise, a null pointer shall be returned.
The application shall not modify the structure to which the return value points, nor any storage areas pointed to by pointers within the structure. The returned pointer, and pointers within the structure, might be invalidated or the structure or the storage areas might be overwritten by a subsequent call to getnetbyaddr(), getnetbyname(), or getnetent(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated.
No errors are defined.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017, <netdb.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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