CSC352 Walking a 2-Level Directory in C
--D. Thiebaut (talk) 07:28, 21 November 2013 (EST)
Create a test structure
Directory structure
- Using bash, from the command line, create a similar structure:
for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do for j in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do echo ${i}${j}; mkdir -p ${i}/${i}${j} done done
Create fake files
- create files using the "touch" command
for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do for j in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do echo ${i}${j}; touch ${i}/${i}${j}/image_${i}${j}.jpg touch ${i}/${i}${j}/image_${j}${i}.png done done
Source
// walk2.c
// D. Thiebaut
// Taken originally from http://stackoverflow.com/questions/612097/
// how-can-i-get-a-list-of-files-in-a-directory-using-c-or-c
// and adapted to fit the current problem.
//
// This program assumes that there is a directory structure containing data files
// The directory structure has this form:
// en/0
// en/0/00
// en/0/01
// en/0/02
// ...
// en/0/0f
// en/1/10
// en/1/12
// ...
// en/1/1f
// en/2/20
// ...
// en/f/ff
//
// This program provides a function called nextFile() that will start by reading
// the directory en/0/00 and return all the files in it, ONE AT A TIME.
// Then it will move on to en/0/01, and return all the files in it, ONE AT A TIME.
// And so on until it has read the final file in en/f/ff, when it will return NULL
// instead of a file name.
//
// Testing: bash commands to create a directory structure along with 2 dummy image
// files in each directory:
//
// cd ./en
// for i in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do
// for j in 0 1 2 3 4 5 6 7 8 9 a b c d e f ; do
// echo ${i}${j}
// mkdir -p ${i}/${i}${j}
// touch ${i}/${i}${j}/image_${i}${j}.jpg
// touch ${i}/${i}${j}/image_${j}${i}.png
// done
// done
//
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <string.h>
char *path;
char* nextPath() {
int len = strlen( path );
//--- if last char not 'f', simply increment it ---
if ( path[ len-1 ]<'9' ) {
path[len-1] += 1;
return path;
}
else if (path[len-1]=='9' ) {
path[len-1] = 'a';
return path;
}
else if (path[len-1]<'f' ) {
path[len-1] += 1;
return path;
}
//--- increment other digit ---
path[len-1] = '0';
if ( path[len-2] <'9' ) {
path[len-2] += 1;
path[len-4] = path[len-2];
return path;
}
else if ( path[len-2]=='9' ) {
path[len-2] = 'a';
path[len-4] = path[len-2];
return path;
}
else if ( path[len-2]<'f' ) {
path[len-2] += 1;
path[len-4] = path[len-2];
return path;
}
//--- if we had reached the end, return null ---
path[len-1] = '0';
path[len-2] = '0';
path[len-4] = '0';
return NULL;
}
int firstTime = 1;
DIR *dir;
char *nextFile() {
//--- if first time, open dir ---
if ( firstTime ) {
firstTime = 0;
dir = opendir ( path );
if ( dir == NULL)
return NULL;
}
//--- if we've read everything already, return NULL ---
if ( path==NULL )
return NULL;
//--- get next file ---
struct dirent *ent;
ent = readdir (dir);
if ( ent == NULL ) {
closedir( dir );
path = nextPath();
firstTime = 1;
return nextFile();
}
//--- skip . and .. files ---
if ( strcmp( ent->d_name, "." )== 0
|| strcmp( ent->d_name, ".." )== 0 )
return nextFile();
//--- return file ---
return ent->d_name;
}
int main( int argc, char **argv) {
int count = 0;
char *fileName = NULL;
path = (char *) malloc( sizeof( "en/0/00" ) * sizeof( char ) );
strcpy( path, "en/0/00" );
if ( argc < 2 ) {
fprintf( stderr, "Syntax: ./walk path" );
exit( 0 );
}
while ( (fileName = nextFile()) != NULL ) {
//if ( strcmp( fileName, "." )==0
// || strcmp( fileName, ".." )==0 )
// continue;
printf( "%s\n", fileName );
}
}