dirent.h

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#ifndef DIRENT_H
#define DIRENT_H
 
// Allow custom memory allocators
#ifndef DIRENT_MALLOC
    #define DIRENT_MALLOC(sz)   malloc(sz)
#endif
#ifndef DIRENT_FREE
    #define DIRENT_FREE(p)      free(p)
#endif
 
//----------------------------------------------------------------------------------
// Types and Structures Definition
//----------------------------------------------------------------------------------
 
// Fordward declaration of DIR, implementation below
typedef struct DIR DIR;
 
struct dirent {
    char *d_name;
};
 
#ifdef __cplusplus
extern "C" {
#endif
 
//------------------------------------------------------------------------------------
// Functions Declaration
//------------------------------------------------------------------------------------
DIR *opendir(const char *name);
int closedir(DIR *dir);
struct dirent *readdir(DIR *dir);
void rewinddir(DIR *dir);
 
#ifdef __cplusplus
}
#endif
 
#endif      // DIRENT_H
 
 
#include <io.h>         // _findfirst and _findnext set errno iff they return -1
#include <stdlib.h>
#include <string.h>
#include <errno.h>
 
//----------------------------------------------------------------------------------
// Types and Structures Definition
//----------------------------------------------------------------------------------
typedef ptrdiff_t handle_type;  // C99's intptr_t not sufficiently portable
 
struct DIR {
    handle_type handle;         // -1 for failed rewind
    struct _finddata_t info;
    struct dirent result;       // d_name null iff first time
    char *name;                 // null-terminated char string
};
 
DIR *opendir(const char *name)
{
    DIR *dir = 0;
 
    if (name && name[0])
    {
        size_t base_length = strlen(name);
        
        // Search pattern must end with suitable wildcard
        const char *all = strchr("/\\", name[base_length - 1]) ? "*" : "/*";
 
        if ((dir = (DIR *)DIRENT_MALLOC(sizeof *dir)) != 0 &&
            (dir->name = (char *)DIRENT_MALLOC(base_length + strlen(all) + 1)) != 0)
        {
            strcat(strcpy(dir->name, name), all);
 
            if ((dir->handle = (handle_type) _findfirst(dir->name, &dir->info)) != -1)
            {
                dir->result.d_name = 0;
            }
            else  // rollback
            {
                DIRENT_FREE(dir->name);
                DIRENT_FREE(dir);
                dir = 0;
            }
        }
        else  // rollback
        {
            DIRENT_FREE(dir);
            dir   = 0;
            errno = ENOMEM;
        }
    }
    else errno = EINVAL;
 
    return dir;
}
 
int closedir(DIR *dir)
{
    int result = -1;
 
    if (dir)
    {
        if (dir->handle != -1) result = _findclose(dir->handle);
 
        DIRENT_FREE(dir->name);
        DIRENT_FREE(dir);
    }
 
    // NOTE: All errors ampped to EBADF
    if (result == -1) errno = EBADF;
 
    return result;
}
 
struct dirent *readdir(DIR *dir)
{
    struct dirent *result = 0;
 
    if (dir && dir->handle != -1)
    {
        if (!dir->result.d_name || _findnext(dir->handle, &dir->info) != -1)
        {
            result = &dir->result;
            result->d_name = dir->info.name;
        }
    }
    else errno = EBADF;
 
    return result;
}
 
void rewinddir(DIR *dir)
{
    if (dir && dir->handle != -1)
    {
        _findclose(dir->handle);
        dir->handle = (handle_type) _findfirst(dir->name, &dir->info);
        dir->result.d_name = 0;
    }
    else errno = EBADF;
}