#include <sys/sysinfo.h>
#include <unistd.h>
#include <string.h>

void show(struct sysinfo *_sys)
{
printf("Total usable main memory size %d\nAvailable memory size %d\n",_sys->totalram, _sys->freeram);
printf("Amount of shared memory %d\nMemory used by buffers %d\n",_sys->sharedram,_sys->bufferram);
printf("Total swap space size %d\nswap space still available %d\n", _sys->totalswap, _sys->freeswap);
printf("Number of current processes %d\n", _sys->procs);
printf("Memory unit size in bytes %ld\n",  _sys->mem_unit);
}

main()
{
static char suc[]="------------- alloc successful ! --------------",
    fai[]="--------------- Fail to alloc ! ----------------";
struct sysinfo _sys;
char *pt;
sysinfo(&_sys);
show(&_sys);
pt=(char *)malloc(80000000); /* 此值可以增大，以强化测试效果 */
if(pt){ strcpy(pt, suc);  puts(pt); }
else puts(fai);
sysinfo(&_sys);
show(&_sys);
}

------解决方案--------------------
Total usable main memory size 2117382144
Available memory size 90734592
Amount of shared memory 0
Memory used by buffers 95215616
Total swap space size 0
swap space still available 0
Number of current processes 86
Memory unit size in bytes 1
------------- alloc successful ! --------------
Total usable main memory size 2117382144
Available memory size 90734592
Amount of shared memory 0
Memory used by buffers 95215616
Total swap space size 0
swap space still available 0
Number of current processes 86
Memory unit size in bytes 1

//释放了~