#include <grp.h>
struct group *getgrgid(gid_t gid);
int getgrgid_r(gid_t gid, struct group *grp,
char
*buffer,
size_t bufsize, struct group **result);
The getgrgid() function shall search the group database for an entry with a matching gid.
The getgrgid() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.
The getgrgid_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 gid. Storage referenced by the group structure is allocated from the memory provided with the buffer parameter, which is bufsize bytes in size. The maximum size needed for this buffer can be determined with the {_SC_GETGR_R_SIZE_MAX} sysconf() parameter. A NULL pointer shall be returned at the location pointed to by result on error or if the requested entry is not found.
Upon successful completion, getgrgid() shall return a pointer to a struct group with the structure defined in <grp.h> with a matching entry if one is found. The getgrgid() function shall return a null pointer if either the requested entry was not found, or an error occurred. On error, errno shall be set to indicate the error.
The return value may point to a static area which is overwritten by a subsequent call to getgrent(), getgrgid(), or getgrnam().
If successful, the getgrgid_r() function shall return zero; otherwise, an error number shall be returned to indicate the error.
The getgrgid() and getgrgid_r() functions may fail if:
The getgrgid_r() function may fail if:
The following sections are informative.
The following example uses getgrgid() to search the group database for a group ID that was previously stored in a stat structure, then prints out the group name if it is found. If the group is not found, the program prints the numeric value of the group for the entry.
#include <sys/types.h>
#include <grp.h>
#include <stdio.h>
...
struct stat statbuf;
struct group *grp;
...
if ((grp = getgrgid(statbuf.st_gid)) != NULL)
printf(" %-8.8s", grp->gr_name);
else
printf(" %-8d", statbuf.st_gid);
...
Applications wishing to check for error situations should set errno to 0 before calling getgrgid(). If errno is set on return, an error occurred.
The getgrgid_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.
endgrent(), getgrnam(), the Base Definitions volume of IEEE Std 1003.1-2001, <grp.h>, <limits.h>, <sys/types.h>