Windows中的GetTickCount非常好用，到了Linux下，我一开始还真没找到替代函数（有点菜），当时恰好项目中的一个模块要用到这个功能，我只好用了gettimeofday来间接满足了要求，但这并不是真正的系统启动后运行的时间。
前几天Review代码，觉得有必要再去研究一下，嘿嘿，还真发现了。
SYSINFO(2) Linux Programmer’s Manual SYSINFO(2)
NAME
sysinfo - returns information on overall system statistics
SYNOPSIS
#include <sys/sysinfo.h>
int sysinfo(struct sysinfo *info);
DESCRIPTION
Until Linux 2.3.16, sysinfo() used to return information in
the following structure:
struct sysinfo {
long uptime; /* Seconds since boot */
unsigned long loads[3]; /* 1, 5, and 15 minute load averages */
unsigned long totalram; /* Total usable main memory size */
unsigned long freeram; /* Available memory size */
unsigned long sharedram; /* Amount of shared memory */
unsigned long bufferram; /* Memory used by buffers */
unsigned long totalswap; /* Total swap space size */
unsigned long freeswap; /* swap space still available */
unsigned short procs; /* Number of current processes */
char _f[22]; /* Pads structure to 64 bytes */
};
and the sizes were given in bytes.
Since Linux 2.3.23 (i386), 2.3.48 (all architectures) the
structure is:
struct sysinfo {
long uptime; /* Seconds since boot */
unsigned long loads[3]; /* 1, 5, and 15 minute load averages */
unsigned long totalram; /* Total usable main memory size */
unsigned long freeram; /* Available memory size */
unsigned long sharedram; /* Amount of shared memory */
unsigned long bufferram; /* Memory used by buffers */
unsigned long totalswap; /* Total swap space size */
unsigned long freeswap; /* swap space still available */
unsigned short procs; /* Number of current processes */
unsigned long totalhigh; /* Total high memory size */
unsigned long freehigh; /* Available high memory size */
unsigned int mem_unit; /* Memory unit size in bytes */
char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding for libc5 */
};
and the sizes are given as multiples of mem_unit bytes.
sysinfo() provides a simple way of getting overall system
statistics. This is more portable than reading /dev/kmem.
For an example of its use, see intro(2).
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno is set appropriately.
ERRORS
EFAULT pointer to struct sysinfo is invalid
CONFORMING TO
This function is Linux specific, and should not be used in
programs intended to be portable.
The Linux kernel has a sysinfo() system call since 0.98.pl6.
Linux libc contains a sysinfo() routine since 5.3.5, and glibc
has one since 1.90.
SEE ALSO
proc(5)
Linux 1997-08-25 SYSINFO(2)