目录
递归实现
非递归实现
我们知道，许多操作系统中的目录结构都是使用树结构。
使用递归的方法定义树是比较容易的。一棵树地一些节点的集合。
这个集合可以为空，若非空，则树由树根和0个或者多个非空的子树组成。
子树中的根都被来自树根的一条有向的边所连接。
因此，可以很自然地想到使用递归的方式来遍历指定的目录。
除了递归，还可以考虑使用非递归方式实现，这样效率会更高，但也更复杂。
递归实现
思路：递归实现较简单，对于一个给定的目录，遍历目录下所有文件，有三种情况：
本目录或父目录，忽略普通文件，输出目录，递归调用
源代码如下：
#include <stdio.h>#include <string.h>#include <sys/types.h>#include <dirent.h>#include <sys/stat.h>#define MAX_PATH_LEN (256)static void trave_dir(char* path) {DIR *d = NULL;struct dirent *dp = NULL; /* readdir函数的返回值就存放在这个结构体中 */struct stat st; char p[MAX_PATH_LEN] = {0};if(stat(path, &st) < 0 || !S_ISDIR(st.st_mode)) {printf("invalid path: %s\n", path);return;}if(!(d = opendir(path))) {printf("opendir[%s] error: %m\n", path);return;}while((dp = readdir(d)) != NULL) {/* 把当前目录.，上一级目录..及隐藏文件都去掉，避免死循环遍历目录 */if((!strncmp(dp->d_name, ".", 1)) || (!strncmp(dp->d_name, "..", 2)))continue;snprintf(p, sizeof(p) - 1, "%s/%s", path, dp->d_name);stat(p, &st);if(!S_ISDIR(st.st_mode)) {printf("%s\n", dp->d_name);} else {printf("%s/\n", dp->d_name);trave_dir(p);}}closedir(d);return;}int main(int argc, char **argv){ char *path = NULL;if (argc != 2) {printf("Usage: %s [dir]\n", argv[0]);printf("use DEFAULT option: %s .\n", argv[0]);printf("-------------------------------------------\n");path = "./";} else {path = argv[1];}trave_dir(path);return 0;}
非递归实现
非递归实现的方法会有很多，一个思路是，每次遍历目录时，把查找到的文件直接输出，目录则保存，用于下次遍历目录下的内容。
此处使用链表实现，结构体用于存储目录路径和下一个目录，遍历目录的过程同上，代码如下：
#include <stdio.h>#include <dirent.h> #include <stdlib.h> #include <string.h>#include <unistd.h>#include <error.h>#include <sys/stat.h> #define MAX_FILE_NAME_LEN 256typedef struct foldernode_t {char *path;// point to foldername or filename pathstruct foldernode_t *next; } foldernode;static void travel_files(char *path){DIR *dir;struct dirent *ptr;char foldername[MAX_FILE_NAME_LEN] = {0};char folderpath[MAX_FILE_NAME_LEN] = {0};foldernode *folderstart;folderstart = calloc(1, sizeof(foldernode));/* ignore err case */folderstart->path = calloc(1, MAX_FILE_NAME_LEN + 1); strncpy(folderstart->path, path, MAX_FILE_NAME_LEN);folderstart->next = NULL;foldernode *folderfirst = folderstart; /* use to search */foldernode *folderlast = folderstart; /* use to add foldernode */foldernode *oldfirst = NULL;while(folderfirst != NULL) {printf("dir=%s\n", folderfirst->path);if ((dir = opendir(folderfirst->path)) != NULL) {while ((ptr = readdir(dir)) != NULL) {if(strcmp(ptr->d_name, ".") == 0 || strcmp(ptr->d_name, "..") == 0) {continue; } else if (ptr->d_type == DT_REG) { /* regular file */printf("%s\n", ptr->d_name);} else if (ptr->d_type == DT_DIR) { /* dir */bzero(foldername, sizeof(foldername));bzero(folderpath, sizeof(folderpath));strncpy(foldername, ptr->d_name, sizeof(foldername));snprintf(folderpath, sizeof(folderpath), "%s/%s", folderfirst->path , foldername);printf("%s\n", folderpath);foldernode *foldernew;foldernew = calloc(1, sizeof(foldernode));foldernew->path = calloc(1, MAX_FILE_NAME_LEN + 1); strncpy(foldernew->path, folderpath, MAX_FILE_NAME_LEN);foldernew->next = NULL;folderlast->next = foldernew;folderlast = foldernew;}}} else {printf("opendir[%s] error: %m\n", folderfirst->path);return;}oldfirst = folderfirst;folderfirst = folderfirst->next; // change folderfirst point to next foldernodeif (oldfirst) {if (oldfirst->path) {free(oldfirst->path);oldfirst->path = NULL;}free(oldfirst);oldfirst = NULL;}closedir(dir);}}int main(int argc,char **argv){if (argc != 2) {printf("Usage: %s path\n", argv[0]);return 0;}travel_files(argv[1]);return 0;}
对目录的遍历是比较基本的功能，对于理解文件系统和数据结构有一定的帮助。
也可以参考bash命令中ls的源码，增加对命令行参数的支持，实现更加复杂的功能。
