linux - [Solved-5 Solutions] What is ultimately a time_t typedef to ? - ubuntu - red hat - debian - linux server - linux pc
Linux - Problem :
What is ultimately a time_t typedef to ?
Linux - Solution 1:
- The time_t datatype is a data type in the ISO C library defined for storing system time values.
- Such values are returned from the standard time() library function.
- This type is a typedef defined in the standard header. ISO C defines time_t as an arithmetic type, but does not specify any particular type, range, resolution, or encoding for it.
- Also unspecified are the meanings of arithmetic operations applied to time values.
- Unix and POSIX-compliant systems implement the time_t type as a signed integer which represents the number of seconds since the start of the Unix epoch
Linux - Solution 2:
[root]# cat time.cclick below button to copy the code. By - Linux tutorial - team
#include <time.h>
int main(int argc, char** argv)
{
time_t test;
return 0;
}click below button to copy the code. By - Linux tutorial - team
[root]# gcc -E time.c | grep __time_tclick below button to copy the code. By - Linux tutorial - team
typedef long int __time_t;click below button to copy the code. By - Linux tutorial - team
It's defined in $INCDIR/bits/types.h
# 131 "/usr/include/bits/types.h" 3 4
# 1 "/usr/include/bits/typesizes.h" 1 3 4
# 132 "/usr/include/bits/types.h" 2 3 4click below button to copy the code. By - Linux tutorial - team
Linux - Solution 3:
- Typically you will find these underlying implementation-specific typedefs for gcc in the bits or asm header directory.
- For Example: /usr/include/x86_64-linux-gnu/bits/types.h
Linux - Solution 4:
Under Visual Studio 2008, it defaults to an __int64 unless you define _USE_32BIT_TIME_T.
Linux - Solution 5:
time_t is of type long int on 64 bit machines, else it is long long int.
You could verify this in these header files:
time.h: /usr/include
types.h and typesizes.h: /usr/include/x86_64-linux-gnu/bitclick below button to copy the code. By - Linux tutorial - team
1)In time.h
typedef __time_t time_t;click below button to copy the code. By - Linux tutorial - team
2)In types.h
# define __STD_TYPE typedef
__STD_TYPE __TIME_T_TYPE __time_t; click below button to copy the code. By - Linux tutorial - team
3)In typesizes.h
#define __TIME_T_TYPE __SYSCALL_SLONG_TYPE
#if defined __x86_64__ && defined __ILP32__
# define __SYSCALL_SLONG_TYPE __SQUAD_TYPE
#else
# define __SYSCALL_SLONG_TYPE __SLONGWORD_TYPE
#endif click below button to copy the code. By - Linux tutorial - team
4) Again in types.h
#define __SLONGWORD_TYPE long int
#if __WORDSIZE == 32
# define __SQUAD_TYPE __quad_t
#elif __WORDSIZE == 64
# define __SQUAD_TYPE long int
#if __WORDSIZE == 64
typedef long int __quad_t;
#else
__extension__ typedef long long int __quad_t;