функции базы данных пользователей (user database functions)
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)
endpwent, getpwent, setpwent — user database functions
Синопсис (Synopsis)
#include <pwd.h>
void endpwent(void);
struct passwd *getpwent(void);
void setpwent(void);
Описание (Description)
These functions shall retrieve information about users.
The getpwent() function shall return a pointer to a structure
containing the broken-out fields of an entry in the user
database. Each entry in the user database contains a passwd
structure. If the user database is not already open, getpwent()
shall open it and return a pointer to a passwd structure
containing the first entry in the database. Thereafter, it shall
return a pointer to a passwd structure containing the next entry
in the user database. Successive calls can be used to search the
entire user database.
If an end-of-file or an error is encountered on reading,
getpwent() shall return a null pointer.
An implementation that provides extended security controls may
impose further implementation-defined restrictions on accessing
the user database. In particular, the system may deny the
existence of some or all of the user database entries associated
with users other than the caller.
The setpwent() function shall rewind the user database so that
the next getpwent() call returns the first entry, allowing
repeated searches.
The endpwent() function shall close the user database.
The setpwent() and endpwent() functions shall not change the
setting of errno if successful.
On error, the setpwent() and endpwent() functions shall set errno
to indicate the error.
Since no value is returned by the setpwent() and endpwent()
functions, an application wishing to check for error situations
should set errno to 0, then call the function, then check errno.
These functions need not be thread-safe.
Возвращаемое значение (Return value)
On successful completion, getpwent() shall return a pointer to a
passwd structure. On end-of-file, getpwent() shall return a null
pointer and shall not change the setting of errno. On error,
getpwent() shall return a null pointer and 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
getpwuid(), getpwnam(), or getpwent(). The returned pointer, and
pointers within the structure, might also be invalidated if the
calling thread is terminated.
Ошибки (Error)
These functions may fail if:
EINTR A signal was caught during the operation.
EIO An I/O error has occurred.
In addition, getpwent() and setpwent() may fail if:
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 following sections are informative.
Примеры (Examples)
Searching the User Database
The following example uses the getpwent() function to get
successive entries in the user database, returning a pointer to a
passwd structure that contains information about each user. The
call to endpwent() closes the user database and cleans up.
#include <pwd.h>
#include <stdio.h>
void printname(uid_t uid)
{
struct passwd *pwd;
setpwent();
while((pwd = getpwent()) != NULL) {
if (pwd->pw_uid == uid) {
printf("name=%s\n",pwd->pw_name);
break;
}
}
endpwent();
}
Использование в приложениях (Application usage)
These functions are provided due to their historical usage.
Applications should avoid dependencies on fields in the password
database, whether the database is a single file, or where in the
file system name space the database resides. Applications should
use getpwuid() whenever possible because it avoids these
dependencies.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
endgrent(3p), getlogin(3p), getpwnam(3p), getpwuid(3p)
The Base Definitions volume of POSIX.1‐2017, pwd.h(0p)
