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#include <grp.h>
struct group *getgrnam(const char *name);
struct group *getgrnam_r(const char *name, struct group *grp, char *buffer, int buflen);
struct group *getgrent(void);
struct group *getgrent_r(struct group *grp, char *buffer, int buflen);
struct group *getgrgid(gid_t gid);
struct group *getgrgid_r(gid_t gid, struct group *grp, char *buffer, int buflen);
void setgrent(void);
void endgrent(void);
struct group *fgetgrent(FILE *f);
struct group *fgetgrent_r(FILE *f, struct group *grp, char *buffer, int buflen);
cc [ flag... ] file ... -D_POSIX_PTHREAD_SEMANTICS [ library... ]
int getgrnam_r(const char *name, struct group *grp, char *buffer, size_t bufsize, struct group **result);
int getgrgid_r(gid_t gid, struct group *grp, char *buffer, size_t bufsize, struct group **result);
See the subsection ‘‘Reentrant Interfaces’’ in the DESCRIPTION section of this page.
These functions are used to obtain entries describing user groups. Entries can come from any of the sources for group specified in the /etc/nsswitch.conf file (see nsswitch.conf(4) ).
getgrnam() searches for an entry with the group name specified by the character string parameter name.
getgrgid() searches for an entry with the (numeric) group id specified by gid.
The functions setgrent(), getgrent(), and endgrent() are used to enumerate group entries from the database. setgrent() sets (or resets) the enumeration to the beginning of the set of group entries. This function should be called before the first call to getgrent(). Calls to getgrnam() and getgrgid() leave the enumeration position in an indeterminate state. Successive calls to getgrent() return either successive entries or NULL, indicating the end of the enumeration.
endgrent() may be called to indicate that the caller expects to do no further group entry retrieval operations; the system may then close the group file, deallocate resources it was using, and so forth. It is still allowed, but possibly less efficient, for the process to call more group functions after calling endgrent().
fgetgrent(), unlike the other functions above, does not use nsswitch.conf; it reads and parses the next line from the stream f, which is assumed to have the format of the group file (see group(4) ).
The functions getgrnam(), getgrgid(), getgrent(), and fgetgrent() use static storage that is re-used in each call, making them unsafe for multithreaded applications.
The parallel functions getgrnam_r(), getgrgid_r(), getgrent_r(), and fgetgrent_r() provide reentrant interfaces for these operations.
Each reentrant interface performs the same operation as its non-reentrant counterpart, named by removing the ‘‘_r’’ suffix. The reentrant interfaces, however, use buffers supplied by the caller to store returned results, and are safe for use in both single-threaded and multithreaded applications.
Each reentrant interface takes the same parameters as its non-reentrant counterpart, as well as the following additional parameters. The parameter grp must be a pointer to a struct group structure allocated by the caller. On successful completion, the function returns the group entry in this structure. The parameter buffer is a pointer to a buffer supplied by the caller, used as storage space for the group data. All of the pointers within the returned struct group grp point to data stored within this buffer; see RETURN VALUES. The buffer must be large enough to hold all the data associated with the group entry. The parameter buflen (or bufsize for the POSIX versions) should give the size in bytes of buffer. The POSIX versions place a pointer to the modified grp structure in the result parameter, instead of returning a pointer to this structure.
For enumeration in multithreaded applications, the position within the enumeration is a process-wide property shared by all threads. setgrent() may be used in a multithreaded application but resets the enumeration position for all threads. If multiple threads interleave calls to getgrent_r(), the threads will enumerate disjoint subsets of the group database. Like their non-reentrant counterparts, getgrnam_r() and getgrgid_r() leave the enumeration position in an indeterminate state.
Group entries are represented by the struct group structure defined in <grp.h>:
struct group {};
char *gr_name; /* the name of the group */ char *gr_passwd; /* the encrypted group password */ gid_t gr_gid; /* the numerical group ID */ char **gr_mem; /* vector of pointers to member names */
The functions getgrnam(), getgrnam_r(), getgrgid(), and getgrgid_r() each return a pointer to a struct group if they successfully locate the requested entry; otherwise they return NULL . The POSIX functions getgrnam_r() and getgrgid_r() return zero upon success, or the error number in case of failure.
The functions getgrent(), getgrent_r(), fgetgrent(), and fgetgrent_r() each return a pointer to a struct group if they successfully enumerate an entry; otherwise they return NULL , indicating the end of the enumeration.
The functions getgrnam(), getgrgid(), getgrent(), and fgetgrent() use static storage, so returned data must be copied before a subsequent call to any of these functions if the data is to be saved.
When the pointer returned by the reentrant functions getgrnam_r(), getgrgid_r(), getgrent_r(), and fgetgrent_r() is non-NULL , it is always equal to the grp pointer that was supplied by the caller.
Programs that use the interfaces described in this manual page cannot be linked statically since the implementations of these functions employ dynamic loading and linking of shared objects at run time.
Use of the enumeration interfaces getgrent() and getgrent_r() is discouraged; enumeration is supported for the group file, NIS, and NIS +, but in general is not efficient and may not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4) .
Previous releases allowed the use of ‘‘+’’ and ‘‘-’’ entries in /etc/group to selectively include and exclude entries from NIS. The primary usage of these entries is superseded by the name service switch, so the ‘‘+/-’’ form may not be supported in future releases.
If required, the ‘‘+/-’’ functionality can still be obtained for NIS by specifying compat as the source for group.
If the ‘‘+/-’’ functionality is required in conjunction with NIS +, specify both compat as the source for group and nisplus as the source for the pseudo-database group_compat. See group(4) , and nsswitch.conf(4) for details.
Solaris 2.4 and earlier releases provided definitions of the getgrnam_r() and getgrgid_r() functions as specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface for these functions. Support for the Draft 6 interface is provided for compatibility only and may not be supported in future releases. New applications and libraries should use the POSIX standard interface.
For POSIX.1c complaint applications, the _POSIX_PTHREAD_SEMANTICS and _REENTRANT flags are automatically turned on by defining the _POSIX_C_SOURCE flag with a value >= 199506L.