pwd的两个实现，anyway，我已经看不懂了

原始pwd的实现请参照Coreutils.

#include <apue.h>
#include <dirent.h>
#include <sys/types.h>

//BUFSIZ is defined in stdio.h: it is the maximum string size
#define MAXPATH BUFSIZ


//print_pwd prints the pwd to the string abs_pathname and NULL_terminates it
void print_pwd(char *abs_pathname);

//print_path prints to str the path from / to the file specified by cur_inum
void print_path(char *str,ino_t cur_inum);

//inum_to_name puts the filename of the ifle with i-node inum into string buf,
//at most len chars long and 0 terminates it
void inum_to_name(ino_t inum,char *buf,int len);

//get_ino gets the i-node number of file fname,if that fnmae is the name of a file
//in the current working directory ,Returns 0 if successful,-1 if not.
int get_ino(char *fnmae,ino_t *inum);

//****************************************
int main(int argc, char* argv[])
{
    char path[MAXPATH]="\0"; //string to store pwd
    print_pwd(path); //print pwd to string path
    printf("%s\n",path); //print path to stdout
    return 0;
    }


//***************************************
void print_pwd(char *pathname)
{
    ino_t inum;
    get_ino(".",&inum);
    print_path(pathname,inum);
    }


//********************************************
void print_path(char *abs_pathname,ino_t this_inode)
{
    ino_t parent_inode;
    char its_name[BUFSIZ];

    //get inumber of parent
    get_ino("..",&parent_inode);


    //at root if parent inum==cur inum
    if(parent_inode != this_inode){
        chdir(".."); //cd up to parent
        //get filename of current file
        inum_to_name(this_inode,its_name,BUFSIZ);
        //recursively get path to parent directory
        print_path(abs_pathname,parent_inode);
        strcat(abs_pathname,"/");
        strcat(abs_pathname,its_name);
        }
    else
        strcat(abs_pathname,"/");
        }

//*****************************************************
void inum_to_name(ino_t inode_to_find,char *namebuf,int buflen)
{
    DIR *dir_ptr;
    struct dirent *direntp;
    dir_ptr=opendir(".");
    if(dir_ptr==NULL){
        perror(".");
        exit(1);
        }

    //search directory for a file with specified inum
    while((direntp=readdir(dir_ptr))!=NULL)
        if(direntp->d_ino==inode_to_find){
            strncpy(namebuf,direntp->d_name,buflen);
            namebuf[buflen-1]='\0';
            closedir(dir_ptr);
            return;
            }
    fprintf(stderr,"\nError looking for i-node number %d\n",inode_to_find);
    exit(1);
    }

//**************************************************************
int get_ino(char *fname,ino_t *inum)
{
    struct stat info;
    if(stat(fname,&info)==-1){
        fprintf(stderr,"Can not stat ");
        perror(fname);
        return -1;
        }
    *inum=info.st_ino;
    return 0;
    }

#include <apue.h>
#include <dirent.h>
#include <sys/types.h>

//BUFSIZ is defined in stdio.h: it is the maximum string size
#define MAXPATH BUFSIZ


//print_pwd prints the pwd to the string abs_pathname and NULL_terminates it
void print_pwd(char *abs_pathname);

//print_path prints to str the path from / to the file specified by cur_inum on the
//device with device id dev_num
void print_path(char *str,ino_t cur_inum,dev_t dev_num);

//inum_to_name puts the filename of the file with i-node inum on device
//with device number dev_num into string buf,at most len chars long and 0
//terminates it
void inum_to_name(ino_t inum,dev_t dev_num,char *buf,int len);

//get_dev_ino gets the device id and the i-node number of file fname,if that fname is the name of a file
//in the current working directory ,Returns 0 if successful,-1 if not.
int get_deviceid_inode(const char *fname,dev_t *dev_id, ino_t *inum);

//****************************************
int main(int argc, char* argv[])
{
    char path[MAXPATH]="\0"; //string to store pwd
    print_pwd(path); //print pwd to string path
    printf("%s\n",path); //print path to stdout
    return 0;
    }


//***************************************
void print_pwd(char *abs_pathname)
{
    ino_t inum;
    dev_t devnum;

    get_deviceid_inode(".",&devnum,&inum);
    print_path(abs_pathname,inum,devnum);
    }


//********************************************
void print_path(char *abs_pathname,ino_t this_inode,dev_t this_dev)
//recusively prints path leading down to file with this inode on this_dev
//use static int height to dtermine which resursive level it is in
{
    ino_t parent_inode;
    char its_name[BUFSIZ];
    dev_t dev_of_node,dev_of_parent;
    static int height=0;

    //get device id and inumber of parent
    get_deviceid_inode("..",&dev_of_parent,&parent_inode);

    //at root if parent inum==cur inum & device ids are same
    if((parent_inode != this_inode)||(dev_of_parent!=this_dev)){
        chdir(".."); //cd up to parent
        //get filename of current file
        inum_to_name(this_inode,this_dev,its_name,BUFSIZ);
        height++; //about to make resursive call
        //recursively get path to parent directory
        print_path(abs_pathname,parent_inode,dev_of_parent);
        strcat(abs_pathname,its_name);
        if (1 < height)
            /* since height is decremented whenever we leave call it can only be > 1
            if we have not popped all calls from the stack
            */
            strcat(abs_pathname,"/");
        height--;
        }
    else //must be at root
        strcat(abs_pathname,"/");
        }

//*****************************************************
void inum_to_name(ino_t inode_to_find,dev_t devnum,char *name,int buflen)
{
    DIR *dir_ptr;
    struct dirent *direntp;
    struct stat statbuf;

    dir_ptr=opendir(".");
    if(dir_ptr==NULL){
        perror(".");
        exit(1);
        }

    //search directory for a file with specified inum
    while((direntp=readdir(dir_ptr))!=NULL){
        if(-1==(stat(direntp->d_name,&statbuf))){
            fprintf(stderr,"could not stat");
            perror(direntp->d_name);
            exit(1);
            }
        if((statbuf.st_ino==inode_to_find)&&(statbuf.st_dev==devnum)){
            strncpy(name,direntp->d_name,buflen);
            name[buflen-1]='\0';
            closedir(dir_ptr);
            return;
            }
        }
    fprintf(stderr,"\nError looking for i-node number %d\n",inode_to_find);
    exit(1);
    }

//**************************************************************
int get_deviceid_inode(const char *fname,dev_t *dev_id,ino_t *inum)
{
    struct stat info;
    if(stat(fname,&info)==-1){
        fprintf(stderr,"Can not stat ");
        perror(fname);
        return -1;
        }
    *inum=info.st_ino;
    *dev_id=info.st_dev;
    return 0;
    }