使用readdir获取文件大小

Question

I am calling readdir() to get info from a directory for file names. I also want to print the file sizes using readdir() only if possible as the structure of dirent is

struct dirent {
               ino_t          d_ino;       /* inode number */
               off_t          d_off;       /* offset to the next dirent */
               unsigned short d_reclen;    /* length of this record */
               unsigned char  d_type;      /* type of file; not supported
                                              by all file system types */
               char           d_name[256]; /* filename */
           };

I am using d_reclen as the file size but somehow my program prints wrong values. But my questions are :

1. Is it right to use d_reclen as the file size? Because my doubt is that it is unsigned short and how can it return correct size for large files.
2. What is actually length of record? Is this size in bytes? How can I calculate correct size?

OUTPUT

Actual Size :1bytes File size :20
Actual Size :4bytes File size :20
Actual Size :8bytes File size :20
Actual Size :256bytes File size :20
Actual Size :0bytes File size :20
Actual Size :255bytes File size :20
Actual Size :1023bytes File size :24

EDIT 1 I am using printf("File size :%hu\\n",pent->d_reclen); to print file size but it is not giving the correct answer.

EDIT 2 I want to avoid the usage of stat() for some performance reasons.

Answer 1

The readdir manual says:

 unsigned short d_reclen; /* length of this record */ 

"This record" is "this struct dirent instance", not "this file".

In your case ( d_reclne 20 or 24) you should not access the whole dirent memory, because readdir allocated only enough memory to fill in d_ino , d_off , d_reclen , d_type and the relevant parts of d_name . readdir did not allocate the complete 256 bytes for d_name .

Answer 2

To get the file size, as opposed to the size (length) of the file name (which is what is recorded in d_reclen ), you need either the stat() or statat() (or lstat() ) system call. You can't get the file size directly from the information in struct dirent .