#include <pwd.h> struct passwd *getpwuid(uid_t uid); int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result);
The getpwuid() function need not be thread-safe.
Applications wishing to check for error situations should set errno to 0 before calling getpwuid(). If getpwuid() returns a null pointer and errno is set to non-zero, an error occurred.
The getpwuid_r() function shall update the passwd structure pointed to by pwd and store a pointer to that structure at the location pointed to by result. The structure shall contain an entry from the user database with a matching uid. Storage referenced by the structure is allocated from the memory provided with the buffer parameter, which is bufsize bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX) returns either -1 without changing errno or an initial value suggested for the size of this buffer. A null pointer shall be returned at the location pointed to by result on error or if the requested entry is not found.
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 getpwent(), getpwnam(), or getpwuid(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated.
If successful, the getpwuid_r() function shall return zero; otherwise, an error number shall be returned to indicate the error.
The getpwuid_r() function may fail if:
The following sections are informative.
long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
size_t len;
if (initlen == -1)
/* Default initial length. */
len = 1024;
else
len = (size_t) initlen;
struct passwd result;
struct passwd *resultp;
char *buffer = malloc(len);
if (buffer == NULL)
...handle error...
int e;
while ((e = getpwuid_r(42, &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);
The following example gets the user database entry for the user with user ID 0 (root).
#include <sys/types.h> #include <pwd.h> ... uid_t id = 0; struct passwd *pwd; pwd = getpwuid(id);
The following example defines pws as a pointer to a structure of type passwd, which is used to store the structure pointer returned by the call to the getpwuid() function. The geteuid() function shall return the effective user ID of the calling process; this is used as the search criteria for the getpwuid() function. The call to getpwuid() shall return a pointer to the structure containing that user ID value.
#include <unistd.h> #include <sys/types.h> #include <pwd.h> ... struct passwd *pws; pws = getpwuid(geteuid());
The following example uses getpwuid() to search the user database for a user ID that was previously stored in a stat structure, then prints out the user name if it is found. If the user is not found, the program prints the numeric value of the user ID for the entry.
#include <sys/types.h> #include <pwd.h> #include <stdio.h> ... struct stat statbuf; struct passwd *pwd; ... if ((pwd = getpwuid(statbuf.st_uid)) != NULL) printf(" %-8.8s", pwd->pw_name); else printf(" %-8d", statbuf.st_uid);
The getpwuid_r() function is thread-safe and returns 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_GETPW_R_SIZE_MAX.
The Base Definitions volume of POSIX.1-2017, <pwd.h>, <sys_types.h>
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