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#include <netdb.h> int setnetgrent(const char *netgroup); void endnetgrent(void); int getnetgrent(char **host, char **user, char **domain); int getnetgrent_r(char **host, char **user, char **domain, char *buf, int buflen); int innetgr(const char *netgroup, const char *host, const char *user, const char *domain);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setnetgrent(), endnetgrent(), getnetgrent(), getnetgrent_r(), innetgr(): _BSD_SOURCE || _SVID_SOURCE
The setnetgrent() call defines the netgroup that will be searched by subsequent getnetgrent() calls. The getnetgrent() function retrieves the next netgroup entry, and returns pointers in host, user, domain. A NULL pointer means that the corresponding entry matches any string. The pointers are valid only as long as there is no call to other netgroup-related functions. To avoid this problem you can use the GNU function getnetgrent_r() that stores the strings in the supplied buffer. To free all allocated buffers use endnetgrent().
In most cases you only want to check if the triplet (hostname,username,domainname) is a member of a netgroup. The function innetgr() can be used for this without calling the above three functions. Again, a NULL pointer is a wildcard and matches any string. The function is thread-safe.