поиск в базе данных группы по имени (search group database for a name)
Пролог (Prolog)
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.
Имя (Name)
getgrnam, getgrnam_r — search group database for a name
Синопсис (Synopsis)
#include <grp.h>
struct group *getgrnam(const char *name);
int getgrnam_r(const char *name, struct group *grp, char *buffer,
size_t bufsize, struct group **result);
Описание (Description)
The getgrnam() function shall search the group database for an
entry with a matching name.
The getgrnam() function need not be thread-safe.
Applications wishing to check for error situations should set
errno to 0 before calling getgrnam(). If getgrnam() returns a
null pointer and errno is set to non-zero, an error occurred.
The getgrnam_r() function shall update the group structure
pointed to by grp and store a pointer to that structure at the
location pointed to by result. The structure shall contain an
entry from the group database with a matching name. Storage
referenced by the group structure is allocated from the memory
provided with the buffer parameter, which is bufsize bytes in
size. A call to sysconf(_SC_GETGR_R_SIZE_MAX) returns either -1
without changing errno or an initial value suggested for the size
of this buffer. A null pointer is returned at the location
pointed to by result on error or if the requested entry is not
found.
Возвращаемое значение (Return value)
The getgrnam() function shall return a pointer to a struct group
with the structure defined in <grp.h> with a matching entry if
one is found. The getgrnam() function shall return a null pointer
if either the requested entry was not found, or an error
occurred. If the requested entry was not found, errno shall not
be changed. On error, errno shall be set to indicate the error.
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
getgrent(), getgrgid(), or getgrnam(). The returned pointer, and
pointers within the structure, might also be invalidated if the
calling thread is terminated.
The getgrnam_r() function shall return zero on success or if the
requested entry was not found and no error has occurred. If any
error has occurred, an error number shall be returned to indicate
the error.
Ошибки (Error)
The getgrnam() and getgrnam_r() functions may fail if:
EIO An I/O error has occurred.
EINTR A signal was caught during getgrnam().
EMFILE All file descriptors available to the process are
currently open.
ENFILE The maximum allowable number of files is currently open in
the system.
The getgrnam_r() function may fail if:
ERANGE Insufficient storage was supplied via buffer and bufsize
to contain the data to be referenced by the resulting
group structure.
The following sections are informative.
Примеры (Examples)
Note that sysconf(_SC_GETGR_R_SIZE_MAX) may return -1 if there is
no hard limit on the size of the buffer needed to store all the
groups returned. This example shows how an application can
allocate a buffer of sufficient size to work with getgrnam_r().
long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
size_t len;
if (initlen == -1)
/* Default initial length. */
len = 1024;
else
len = (size_t) initlen;
struct group result;
struct group *resultp;
char *buffer = malloc(len);
if (buffer == NULL)
...handle error...
int e;
while ((e = getgrnam_r("somegroup", &result, buffer, len, &resultp))
== ERANGE)
{
size_t newlen = 2 * len;
if (newlen < len)
...handle error...
len = newlen;
char *newbuffer = realloc(buffer, len);
if (newbuffer == NULL)
...handle error...
buffer = newbuffer;
}
if (e != 0)
...handle error...
free (buffer);
Использование в приложениях (Application usage)
The getgrnam_r() function is thread-safe and shall return values
in a user-supplied buffer instead of possibly using a static data
area that may be overwritten by each call.
Portable applications should take into account that it is usual
for an implementation to return -1 from sysconf() indicating that
there is no maximum for _SC_GETGR_R_SIZE_MAX.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
endgrent(3p), getgrgid(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2017, grp.h(0p),
sys_types.h(0p)
