Question
Size of pid_t, uid_t, gid_t on Linux
On Linux systems (either 32- or 64-bit), what is the size of pid_t
, uid_t
, and gid_t
?
Question
On Linux systems (either 32- or 64-bit), what is the size of pid_t
, uid_t
, and gid_t
?
Solution
#include <stdio.h>
#include <sys/types.h>
int main()
{
printf("pid_t: %zu\n", sizeof(pid_t));
printf("uid_t: %zu\n", sizeof(uid_t));
printf("gid_t: %zu\n", sizeof(gid_t));
}
EDIT: Per popular request (and because, realistically, 99% of the people coming to this question are going to be running x86 or x86_64)...
On an i686 and x86_64 (so, 32-bit and 64-bit) processor running Linux >= 3.0.0, the answer is:
pid_t: 4
uid_t: 4
gid_t: 4
Solution
On intel architectures, sizes are defined in /usr/include/bits/typesizes.h
:
#define __UID_T_TYPE __U32_TYPE
#define __GID_T_TYPE __U32_TYPE
#define __PID_T_TYPE __S32_TYPE
In other words, uid_t
and gid_t
are unsigned 32-bit integers and pid_t
is a signed 32-bit integer. This applies for both 32- and 64-bits.
I am not sure what they are on other architectures offhand as I don't have any available at the moment, but the definitive way is to compile a program which prints the output of sizeof(uid_t)
, etc.