說明：在linux環境下實現2秒一次的監控cpu使用率。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// cpu info
struct occupy {
 char name[20];
 unsigned int user;
 unsigned int nice;
 unsigned int system;
 unsigned int idle;
};

float g_cpu_used;
int cpu_num;

// read cpu info from /proc/stat這裡讀取檔案得到一些數值，這些數值可用來計算cpu使用率
void get_occupy(struct occupy *p)
{
 FILE *fp;
 int i;
 char buff[1024];
 
 if ((fp = fopen("/proc/stat", "r")) == NULL) {
  fprintf(stderr, "cant open /proc/stat\n");
  fclose(fp);
 }
 fgets(buff, sizeof(buff), fp);
 for (i=0; i<cpu_num; i++) {
  fgets(buff, sizeof(buff), fp);
  sscanf(buff, "%s%u%u%u%u", p[i].name, &(p[i].user), &(p[i].nice), &(p[i].system), &(p[i].idle));
 }
 fclose(fp);
}

// calculate cpu occupation計算cpu使用率
void cal_occupy(struct occupy *p1, struct occupy *p2)
{
 double od, nd;
 od = (double)(p1->user + p1->nice + p1->system + p1->idle);
 nd = (double)(p2->user + p2->nice + p2->system + p2->idle);
 g_cpu_used = ((p2->user + p2->system + p2->nice) - (p1->user + p1->system + p1->nice)) / (nd - od) * 100;
}

int main(int argc, char **argv)
{
 struct occupy ocpu[10];
 struct occupy ncpu[10];
 int i;
 
 pid_t pid = fork();
 if (pid == 0)
  execvp(argv[1], &argv[1]); //start another process to observe cpu
 else {
  cpu_num = sysconf(_SC_NPROCESSORS_ONLN);//得到CPU個數
  while (1) {
   get_occupy(ocpu);
   sleep(1);
   get_occupy(ncpu);
   system("clear");
   for (i=0; i<cpu_num; i++) {
    cal_occupy(&ocpu[i], &ncpu[i]);
    printf("%s %.4f%% \n",ocpu[i].name, g_cpu_used);
   }
   sleep(1);
  }
 }
 
 return 0;
}

Linux+shell如下，可得到top命令的任何資料，包括cpu、記憶體、負載等。

#include<sys/types.h>

#include<unistd.h>

#include<stdlib.h>

#include<stdio.h>

#include<string.h>

intmain()

{

FILE *stream;

char buf[1024];

if( (stream =popen("top","r")) == NULL )

{

printf("error");

exit(0);

}

while(fgets(buf,sizeof(buf),stream))

{

printf("%s",buf);

memset(buf,'/0',sizeof(buf));

}

pclose(stream);

}