Operation_System/linux-0.11-lab/b/mytest.c

#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>

#define BUF_MAX 4096
#define CWD_BUF_SIZE 512


int my_strlen(const char* Src){
  int len = 0;
  int i = 0;
  for(; Src[i]; ++i){
    ++len;
  }
  return len;
}

void my_strcat(char* src, const char* dst){
  int len = my_strlen(src);
  int i;
  for(i = len; dst[i - len]; ++i){
    src[i] = dst[i - len];
  }
  src[i] = '\0';
}
int get_subentry(const char* dir, char* cwdbuf, char** subentry){
  int i, num_file = 0, read_num;
  int fd = open(dir, O_RDONLY);
  if(fd == -1){
    return -1;
  }
  for(i = 0; i < CWD_BUF_SIZE; ++i){
    cwdbuf[i] = '\0';
  }
  read_num = read(fd, cwdbuf, CWD_BUF_SIZE);
  if(read_num == -1){
    return -1;
  }
  close(fd);
  for(i = 0; i < CWD_BUF_SIZE; ){
    if((cwdbuf[i] == '.') || (cwdbuf[i] >= 'a' && cwdbuf[i] <= 'z') || (cwdbuf[i] >= 'A' && cwdbuf[i] <= 'Z')){
      subentry[num_file++] = cwdbuf + i;
      while(i<CWD_BUF_SIZE && cwdbuf[i]){
        ++i;
      }
    }else{
      cwdbuf[i] = '\0';
      ++i;
    }
  }
  subentry[num_file] = NULL;
  return read_num;
}
int find(char* cur_path, char* wd){
  int i;
  int is_find = 1;
  int read_num;
  int path_len;
  char curdir[CWD_BUF_SIZE+1];
  char* cur_subentry[1000];

  read_num = get_subentry(cur_path, curdir, cur_subentry);
  if(read_num == -1){
    return 0;
  }
  if(cur_subentry[0]==NULL || cur_subentry[1] == NULL || cur_subentry[0][0] != '.' || cur_subentry[1][0] != '.' || cur_subentry[1][1]!='.'){
    return 0;
  }
  for(i = 0; i < read_num; ++i){
    if(curdir[i] != wd[i]){
      is_find = 0;
      break;
    }
  }
  if(is_find){
    return 1;
  }
  if(cur_path[1]=='d' && cur_path[2]=='e' && cur_path[3]=='v'){
    return 0;
  }
  path_len = my_strlen(cur_path);
  for(i = 2; cur_subentry[i]; ++i){
    if(cur_subentry[i][0]=='.'){
      continue;
    }
    if(path_len != 1){
      cur_path[path_len] = '/';
      cur_path[path_len+1]='\0';
    }
    my_strcat(cur_path, cur_subentry[i]);
    if(find(cur_path, wd)){
      return 1;
    }else{
      cur_path[path_len] = '\0';
    }
  }
  return 0;
}
char* my_getcwd(char *cur_path, size_t size){
  char cwd[CWD_BUF_SIZE+1];
  char* cwd_entry[100];
  get_subentry(".", cwd, cwd_entry);
  cur_path[0] = '/';
  cur_path[1] = '\0';

  find(cur_path, cwd);
  if(cur_path[0] != '/'){
    return NULL;
  }
  return cur_path;
}

int main(void){
    char buf[100];
    my_getcwd(buf, 128);
    printf("%s\n", buf);
    return 0;
}