获取系统cpu使用率（linux C）

typedef struct cpu_occupy_          //定义一个cpu occupy的结构体
{
    char name[20];                  //定义一个char类型的数组名name有20个元素
    unsigned int user;              //定义一个无符号的int类型的user
    unsigned int nice;              //定义一个无符号的int类型的nice
    unsigned int system;            //定义一个无符号的int类型的system
    unsigned int idle;              //定义一个无符号的int类型的idle
    unsigned int iowait;
    unsigned int irq;
    unsigned int softirq;
}cpu_occupy_t;

double cal_cpuoccupy (cpu_occupy_t *o, cpu_occupy_t *n)
{
    double od, nd;
    double id, sd;
    double cpu_use ;

    od = (double) (o->user + o->nice + o->system +o->idle+o->softirq+o->iowait+o->irq);//第一次(用户+优先级+系统+空闲)的时间再赋给od
    nd = (double) (n->user + n->nice + n->system +n->idle+n->softirq+n->iowait+n->irq);//第二次(用户+优先级+系统+空闲)的时间再赋给od

    id = (double) (n->idle);    //用户第一次和第二次的时间之差再赋给id
    sd = (double) (o->idle) ;    //系统第一次和第二次的时间之差再赋给sd
    if((nd-od) != 0)
        cpu_use =100.0 - ((id-sd))/(nd-od)*100.00; //((用户+系统)乖100)除(第一次和第二次的时间差)再赋给g_cpu_used
    else 
        cpu_use = 0;
    return cpu_use;
}

void get_cpuoccupy (cpu_occupy_t *cpust)
{
    FILE *fd;
    int n;
    char buff[256];
    cpu_occupy_t *cpu_occupy;
    cpu_occupy=cpust;

    fd = fopen ("/proc/stat", "r");
    if(fd == NULL)
    {
            perror("fopen:");
            exit (0);
    }
    fgets (buff, sizeof(buff), fd);

    sscanf (buff, "%s %u %u %u %u %u %u %u", cpu_occupy->name, &cpu_occupy->user, &cpu_occupy->nice,&cpu_occupy->system, &cpu_occupy->idle ,&cpu_occupy->iowait,&cpu_occupy->irq,&cpu_occupy->softirq);

    fclose(fd);
}

double get_sysCpuUsage()
{
    cpu_occupy_t cpu_stat1;
    cpu_occupy_t cpu_stat2;
    double cpu;
    get_cpuoccupy((cpu_occupy_t *)&cpu_stat1);
    sleep(1);

    //第二次获取cpu使用情况
    get_cpuoccupy((cpu_occupy_t *)&cpu_stat2);

    //计算cpu使用率
    cpu = cal_cpuoccupy ((cpu_occupy_t *)&cpu_stat1, (cpu_occupy_t *)&cpu_stat2);

    return cpu;
}