Linux编程中目录内容的读取（实现ls功能）

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dirent.h是POSIX.1标准定义的unix类目录操作的头文件，包含了许多UNIX系统服务的函数原型。

头文件的位置在/usr/include/dirent.h，里面有很多函数定义和宏，可以提供给我们非常丰富的目录处理方法。我们在编程中一般只需要简单的使用下面几个函数。

/* This is the data type of directory stream objects.    The actual structure is opaque to users.  */ typedef struct __dirstream DIR; /* Open a directory stream on NAME.    Return a DIR stream on the directory, or NULL if it could not be opened.    This function is a possible cancellation point and therefore not marked with __THROW.  */ extern DIR *opendir (__const char *__name) __nonnull ((1));/* Close the directory stream DIRP.   Return 0 if successful, -1 if not.   This function is a possible cancellation point and therefore not marked with __THROW.  */extern int closedir (DIR *__dirp) __nonnull ((1));/* Read a directory entry from DIRP.  Return a pointer to a `struct dirent' describing the entry, or NULL for EOF or error.  The storage returned may be overwritten by a later readdir call on the same DIR stream.If the Large File Support API is selected we have to use the appropriate interface.   This function is a possible cancellation point and therefore not marked with __THROW.  */#ifndef __USE_FILE_OFFSET64extern struct dirent *readdir (DIR *__dirp) __nonnull ((1));#else

示例代码，实现ls功能（简单实现了-a参数）：

#include <stdio.h>#include <dirent.h>#include <stdlib.h>#define FLAG_NOHIDE 0x01int main(int argc, char *argv[]){    DIR *dp;    struct dirent *dirp;    int opt;    unsigned char flag=0x00;    if (argc < 2)    {        printf("usage: ls directory_name\n");        exit(0);    }    while ((opt = getopt(argc, argv, "a")) != -1)    {        switch (opt)        {            case 'a':                flag |= FLAG_NOHIDE;                break;        }    }    // open the dir(the 2ed argv index is always argc-1 I guess)    if ((dp = opendir(argv[argc-1])) == NULL)    {        printf("error: can't open %s\n", argv[argc-1]);        exit(0);    }    // use readdir to get all the file struct    while ((dirp = readdir(dp)) != NULL)    {        if (!(flag & FLAG_NOHIDE))        {            if (dirp->d_name[0] == '.')            {                continue;            }        }         printf("%s\n", dirp->d_name);    }    closedir(dp);    return 0;}

附上dirent的结构：

struct dirent{    long d_ino; /* inode number 索引节点号 */    off_t d_off; /* offset to this dirent 在目录文件中的偏移 */    unsigned short d_reclen; /* length of this d_name 文件名长 */    unsigned char d_type; /* the type of d_name 文件类型 */    char d_name [NAME_MAX+1]; /* file name (null-terminated) 文件名，最长256字符 */}

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