#include <pwd.h> struct passwd *getpwnam(const char *name); int getpwnam_r(const char *name, struct passwd *pwd, char *buffer, size_t bufsize, struct passwd **result);
The getpwnam() function need not be thread-safe.
Applications wishing to check for error situations should set errno to 0 before calling getpwnam(). If getpwnam() returns a null pointer and errno is non-zero, an error occurred.
The getpwnam_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 name. 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.
The getpwnam_r() function shall return zero on success or if the requested entry was not found and no error has occurred. If an error has occurred, an error number shall be returned to indicate the error.
The getpwnam_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 = getpwnam_r("someuser", &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 uses the getlogin() function to return the name of the user who logged in; this information is passed to the getpwnam() function to get the user database entry for that user.
#include <sys/types.h> #include <pwd.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> ... char *lgn; struct passwd *pw; ... if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) { fprintf(stderr, "Get of user information failed.\n"); exit(1); } ...
The getpwnam_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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