【C】——APUE小程序之递归遍历目录

　　递归降序遍历目录层次结构，并按文件类型计数。

　　先介绍相关的函数：

#include<dirent.h>

DIR *opendir(const char *pathname);        //打开目录
返回值：成功返回指针，出错返回NULL

struct dirent *readdir(DIR *dp);               //读取目录       
返回值：成功返回指针，出错返回NULL

void rewinddir(DIR *dp);                           //重设读取目录的位置为开头位置

int closedir(DIR *dp);                             //关闭目录       
返回值：成功返回0，出错返回-1

long telldir(DIR *dp);                            //取得目录流的读取位置   
返回值：与dp关联的目录中的当前位置

void seekdir(DIR *dp, long loc);              //设置下回读取目录的位置

struct dirent{
     ino_t d_ino;                         //i-node number
     char   d_name[NAME_MAX + 1];            //null-terminated filename
}

　　改写APUE的代码：

#include<stdio.h>
#include<dirent.h>
#include<sys/stat.h>
#include<string.h>
#include<stdlib.h>

static int nreg = 0, ndir = 0, nblk = 0, nchr = 0, nfifo = 0, nslink = 0, nsock = 0, ntot = 0;

static char *fullpath;

int myfunc(const char *pathname, const struct stat *statptr, int type)
{
    switch(type){
    case 1:
        switch(statptr->st_mode & S_IFMT){
        case S_IFREG: nreg++;    break;
        case S_IFBLK: nblk++;    break;
        case S_IFCHR: nchr++;    break;
        case S_IFIFO: nfifo++;    break;
        case S_IFLNK: nslink++;    break;
        case S_IFSOCK: nsock++;    break;
        case S_IFDIR:{
            printf("for S_IFDIR for %s
",pathname);
            }
        }
        break;
    case 2:        //文件夹
        ndir++;    break;
    case 3:
        printf("cant read directory %s
",pathname);
    case 4:
        printf("stat error for %s
",pathname);    
    }

    return 0;
}

int dopath()
{
    struct stat     statbuf;        //文件信息
    struct dirent     *dirp;        //文件夹信息，包括i-node number   filename
    DIR         *dp;        //打开目录返回的指针
    char         *ptr;

    if((lstat(fullpath,&statbuf)) < 0)
        return(myfunc(fullpath,&statbuf,4));
    if(S_ISDIR(statbuf.st_mode) == 0)        //判断是否是文件夹
        return(myfunc(fullpath,&statbuf,1));

    myfunc(fullpath,&statbuf,2);            //是目录则调用函数使目录数量自加一

    ptr = fullpath + strlen(fullpath);
    *ptr++ = '/';
    *ptr = 0;

    if((dp = opendir(fullpath)) == NULL)
        return(myfunc(fullpath,&statbuf,3));

    while((dirp = readdir(dp)) != NULL){
        if(strcmp(dirp->d_name,".") == 0 || strcmp(dirp->d_name,"..") == 0)
            continue;
        strcpy(ptr, dirp->d_name);

        dopath();
    }

    closedir(dp);

}

void ftw(char *pathname)
{
#ifdef PATH_MAX
    const int PATH_LEN = PATH_MAX;
#else
    const int PATH_LEN = 1024;
#endif
    
    fullpath = malloc(PATH_LEN);
    
    strncpy(fullpath,pathname,PATH_LEN);

    fullpath[PATH_LEN - 1] = '';

    dopath();
}

int main(int argc, char *argv[])
{
    if(argc != 2){
        printf("enter two args
");
        exit(1);
    }

    ftw(argv[1]);

    printf("regular files: }
",nreg);
    printf("directories : }
",ndir);
    printf("block special: }
",nblk);
    printf("char special: }
",nchr);
    printf("FIFOS: }
",nfifo);
    printf("symboli links: }
",nslink);
    printf("sockets: }
",nsock);
    
}

　　需要注意的是第60行的判断一定不能少，因为在linux下创建一个空目录的时候，用ls查看其属性发现里面大小是2.写一个程序看下一个空目录里都有神马？

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

int main(int argc, char *argv[])
{
    DIR *dp;
    struct dirent *dirp;
    char pathname[20];

    if(argc != 2){
        printf("please enter to args
");
        exit(1);   
    }

    puts(argv[1]);

    strncpy(pathname, argv[1], 20);

    if((dp = opendir(pathname)) == NULL){
        printf("opendir %s error
",argv[1]);
        exit(2);
    }

    while((dirp = readdir(dp)) != NULL){
        printf("%s
",dirp->d_name);
    }

    closedir(dp);

    return 0;
}

　　虽然是个空目录但是给的结果却是

.

..

　　因此要忽略掉这两个，否则会进入死循环；