apue编程之参考df代码写的一个简单的df命令的源代码

#include <stdio.h>
#include <mntent.h>
#include <string.h>
#include <sys/vfs.h>
static const unsigned long long G = 1024*1024*1024ull;
static const unsigned long long M = 1024*1024;
static const unsigned long long K = 1024;
static char str[20];
char* kscale(unsigned long b, unsigned long bs)
{
    unsigned long long size = b * (unsigned long long)bs;
    if (size > G)
    {
        sprintf(str, "%0.2f GB", size/(G*1.0));
        return str;
    }
    else if (size > M)
    {
        sprintf(str, "%0.2f MB", size/(1.0*M));
        return str;
    }
    else if (size > K)
    {
        sprintf(str, "%0.2f K", size/(1.0*K));
        return str;
    }
    else
    {
        sprintf(str, "%0.2f B", size*1.0);
        return str;
    }
}
int main(int argc, char *argv[])
{
    FILE* mount_table;
    struct mntent *mount_entry;
    struct statfs s;
    unsigned long blocks_used;
    unsigned blocks_percent_used;
    const char *disp_units_hdr = NULL;
    mount_table = NULL;
    mount_table = setmntent("/etc/mtab", "r");
    if (!mount_table)
    {
        fprintf(stderr, "set mount entry error\n");
        return -1;
    }
    disp_units_hdr = "     Size";
    printf("Filesystem           %-15sUsed Available %s Mounted on\n",
            disp_units_hdr, "Use%");
    while (1) {
        const char *device;
        const char *mount_point;
        if (mount_table) {
            mount_entry = getmntent(mount_table);
            if (!mount_entry) {
                endmntent(mount_table);
                break;
            }
        }
        else
            continue;
        device = mount_entry->mnt_fsname;
        mount_point = mount_entry->mnt_dir;
        //fprintf(stderr, "mount info: device=%s mountpoint=%s\n", device, mount_point);
        if (statfs(mount_point, &s) != 0)
        {
            fprintf(stderr, "statfs failed!\n");   
            continue;
        }
        if ((s.f_blocks > 0) || !mount_table )
        {
            blocks_used = s.f_blocks - s.f_bfree;
            blocks_percent_used = 0;
            if (blocks_used + s.f_bavail)
            {
                blocks_percent_used = (blocks_used * 100ULL
                        + (blocks_used + s.f_bavail)/2
                        ) / (blocks_used + s.f_bavail);
            }
            /* GNU coreutils 6.10 skips certain mounts, try to be compatible.  */
            if (strcmp(device, "rootfs") == 0)
                continue;
            if (printf("\n%-20s" + 1, device) > 20)
                    printf("\n%-20s", "");
            char s1[20];
            char s2[20];
            char s3[20];
            strcpy(s1, kscale(s.f_blocks, s.f_bsize));
            strcpy(s2, kscale(s.f_blocks - s.f_bfree, s.f_bsize));
            strcpy(s3, kscale(s.f_bavail, s.f_bsize));
            printf(" %9s %9s %9s %3u%% %s\n",
                    s1,
                    s2,
                    s3,
                    blocks_percent_used, mount_point);
        }
    }
    return 0;
}

编译：g++ -g -Wall main.cpp
 
可以生成一个a.out的文件，
 
下面是运行a.out和df -h的输出对比：
 
:/tmp/tmp$ df -h
文件系统            容量  已用 可用 已用% 挂载点
/dev/sda7             9.4G  6.5G  2.5G  73% /
none                  1.6G  300K  1.6G   1% /dev
none                  1.6G  212K  1.6G   1% /dev/shm
none                  1.6G  296K  1.6G   1% /var/run
none                  1.6G     0  1.6G   0% /var/lock
none                  1.6G     0  1.6G   0% /lib/init/rw
/dev/sda6             113G   87G   26G  77% /media/work_
/dev/sda9              26G   23G  2.0G  92% /home
 
/tmp/tmp$ ./a.out
Filesystem                Size      Used Available Use% Mounted on
/dev/sda7              9.39 GB   6.45 GB   2.46 GB  72% /
none                   1.59 GB  300.00 K   1.59 GB   0% /dev
none                   1.60 GB 1020.00 K   1.59 GB   0% /dev/shm
none                   1.60 GB  296.00 K   1.59 GB   0% /var/run
none                   1.60 GB    0.00 B   1.60 GB   0% /var/lock
none                   1.60 GB    0.00 B   1.60 GB   0% /lib/init/rw
/dev/sda6            112.62 GB  86.67 GB  25.95 GB  77% /media/work_
/dev/sda9             25.38 GB  22.10 GB   1.99 GB  92% /home