Get CPU usage by precentage

sys_usage.c

/*
 * =====================================================================================
 *
 *       Filename:  sys_usage.c
 *
 *    Description:  get usage of CPU and I/O
 *
 *        Version:  1.0
 *        Created:  04/09/2012 02:23:08 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  YOUR NAME (), 
 *   Organization:  
 *
 * =====================================================================================
 */
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

struct cpu_stat{
		unsigned long user;
		unsigned long nice;
		unsigned long sys;
		unsigned long idle;
		unsigned long iowait;
		unsigned long irq;
		unsigned long softirq;
};

struct cpu_stat get_cpu_stat()
{
		FILE *file;
		char cpu[4];
		struct cpu_stat stat;
		file = fopen("/proc/stat", "r");
		
		fscanf(file, "%4s %ld %ld %ld %ld %ld %ld %ld", cpu,
						&stat.user, &stat.nice, &stat.sys, &stat.idle,
						&stat.iowait, &stat.irq, &stat.softirq);
		fclose(file);
		return stat;
}

void print_cpu_stat(struct cpu_stat stat)
{
		printf("user:%ld nice:%ld sys:%ld idle:%ld iowait:%ld irq:%ld softirq:%ld\n", stat.user, stat.nice, stat.sys, stat.idle, stat.iowait, stat.irq, stat.softirq);
}

void print_cpu_usage(struct cpu_stat pre, struct cpu_stat after)
{
		float total;
		float idle;
		total = after.user+after.nice+after.sys+after.idle+after.iowait+after.irq+after.softirq - 
				(pre.user + pre.nice + pre.sys + pre.idle + pre.iowait + pre.irq + pre.softirq);
		idle = after.idle - pre.idle;
		printf("CPU usage is %.2f\n", (total-idle) / total * 100);
}

int main(int argc, char ** argv)
{
		struct cpu_stat pre, after;

		pre = get_cpu_stat();

		while(1){
				sleep(1);
				after = get_cpu_stat();
				print_cpu_usage(pre, after);
				pre = after;
		}

		return 0;

}