如何在c中为以下要求创建递归目录？

Question

i expect to have more than one million files with unique names. I have been told that if i put all this files in one or two directories the search speed for these files will be extremely slow. So i have come up with the following directory architecture.

I want the directory structure to branch out with 10 sub directories and the level of the sub directories will be 4. because the file names are guaranteed to be unique i want to use these file names to make hashes which can be used to put the file in a directory and also later to find it. The random hash values will make a directory to have,approximately, 1,000 files.

so if F is root directory then inserting or searching for a file will have to go through these steps:

I want to use numbers from 0-9 as directory names

h=hash(filename)
sprintf(filepath,"f//%d//%d//%d//%d//.txt",h%10,h%10,h%10,h%10);

HOW DO I CREATE THESE DIRECTORIES?

EDIT:

All the files are text files. The program will be distributed to many people in order to collect information for a research. So tt is important that these files are created like this.

EDIT:

i created the following code to implement perreal's pseudo code. It compiles to success but gives the run time error given at the end. error occurs at the sprintf() line.

#include<iostream>
#include<stdlib.h>

#include<windows.h>
void make_dir(int depth, char *dir) {
        if (depth < 4) {
               if (!  CreateDirectoryA (dir,NULL))
                for (int i = 0; i < 10; i++) {
                    sprintf(dir,"\\%d",i);
                    char *sdir=NULL ;
                        strcpy(sdir,dir);
                        CreateDirectoryA(sdir,NULL);
                        make_dir(depth + 1, sdir);
                }
        }
}
int  main()
{
    make_dir(0,"dir");
    return 1;
}

Unhandled exception at 0x5b9c1cee (msvcr100d.dll) in mkdir.exe: 0xC0000005: Access violation writing location 0x00be5898.

Answer 1

Kind of pseudo code, but can be done like this:

 void make_dir(int depth, char *dir) {
  if (depth < 4) {
    CreateDirectoryA (dir,NULL);
    for (int i = 0; i < 10; i++) {
        char *sdir= (char*)malloc(strlen(dir+10)); // XXX 10?
        strcpy(sdir, dir);
        sprintf(sdir + strlen(sdir), "\\%d", i); 
        printf("%s\n", sdir);
        //CreateDirectoryA(sdir,NULL);
        make_dir(depth + 1, sdir);
        free(sdir);
    }   
  }     
}

}

And to call make_dir(0, rootdir);

Answer 2

Do not do this:

sprintf(dir,"\%d",i);

1. dir is a const, read only string in your example.
2. You're likely to run off the end of the string, corrupting things that follow it in memory.

Do not copy to sdir without allocating memory first.

sdir = (char *)malloc( strlen( dir ) + 1 );

At the end of the function make_dir , you will have to call free( sdir ); so you do not leak memory.