写一段在Linux下使用C语言计算CPU使用率的代码

当然，我很乐意帮你回答这个问题。以下是在Linux下使用C语言计算CPU使用率的代码：

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

int main() {
    long double total_jiffies_start, work_jiffies_start, total_jiffies_end, work_jiffies_end;
    char stat[1024];

    FILE* fp = NULL;
    if ((fp = fopen("/proc/stat", "r")) == NULL) {
        fprintf(stderr, "Error: failed to open /proc/stat\n");
        exit(EXIT_FAILURE);
    }

    fgets(stat, 1024, fp);
    sscanf(stat, "cpu %Lf %Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf", &total_jiffies_start, &work_jiffies_start);

    fclose(fp);

    sleep(1);

    if ((fp = fopen("/proc/stat", "r")) == NULL) {
        fprintf(stderr, "Error: failed to open /proc/stat\n");
        exit(EXIT_FAILURE);
    }

    fgets(stat, 1024, fp);
    sscanf(stat, "cpu %Lf %Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf %*Lf", &total_jiffies_end, &work_jiffies_end);

    fclose(fp);

    long double total_jiffies = total_jiffies_end - total_jiffies_start;
    long double work_jiffies = work_jiffies_end - work_jiffies_start;

    double cpu_usage = work_jiffies / total_jiffies * 100;

    printf("CPU Usage: %.2f%%\n", cpu_usage);

    return 0;
}

这段代码会读取 `/proc/stat` 文件来获取 CPU 执行周期（jiffies）的信息，然后通过睡眠 1 秒来计算出 CPU 使用率，并输出到标准输出中。