list only certain filetype in directory

[Neon612]

I've read up somewhat on boostfilesystem and the normal scandir way of listing files in a directory. The example programs I have tried worked great, but I'd like to limit the list feature to only look for a certain filetype, mp3.

What would be the best way of doing this? Boost or scandir? This does not have to work on multiple platforms, and I'm also just learning C++ at the moment (only a month of writing code behind me) so I'd like a simpler way of doing this for the time being.

Thank you.

[Reiger]

Well you could use a regular expression; if supported?

For instance, in bash:


ls *.mp3

[Neon612]

I have some C++ sample code that I'd like to change to let it search only for mp3 files.

#include <stdio.h>
#include <dirent.h>

static int one (const struct dirent *unused)
{
return 1;
}

int main (void)
{
struct dirent **eps;
int n;

n = scandir ("./", &eps, one, alphasort);
if (n >= 0)
{
int cnt;
for (cnt = 0; cnt < n; ++cnt)
puts (eps[cnt]->d_name);
}
else
perror ("Couldn't open the directory");

return 0;
}

[thegom]

The third argument scandir takes is "filter", which is a pointer to a function you write yourself to filter out entries - one way is to do it like this:


#include <stdio.h>
#include <dirent.h>
#include <string>
int mp3filter(const struct dirent *dir)
// post: returns 1/true if name of dir ends in .mp3
{
const char *s = dir->d_name;
int len = strlen(s) - 4; // index of start of . in .mp3
if(len >= 0)
{
if (strncmp(s + len, ".mp3", 4) == 0)
{
return 1;
}
}
return 0;
}

static int one (const struct dirent *unused)
{
return 1;
}

int main (void)
{
struct dirent **eps;
int n;

n = scandir ("./", &eps, mp3filter, alphasort);
if (n >= 0)
{
int cnt;
for (cnt = 0; cnt < n; ++cnt)
puts (eps[cnt]->d_name);
}
else
perror ("Couldn't open the directory");

return 0;
}

[Neon612]

Thank you that works like a charm.

Now with the output, the puts command is what outputs each filename, right?
What does the (eps[cnt]->d_name) command mean or do?

[thegom]

Yeah, according to this (http://www.cplusplus.com/reference/clibrary/cstdio/puts.html) puts("something") behaves like printf("something); or cout << "something";, except it automatically includes a newline at the end - I've never used it before tho.

As for the (eps[cnt]->d_name, you have an array of pointers to dirent's called eps. the -> operator lets you access an attribute from a pointer to an object/struct, where normally you would use structname.attributename to access the attribute if it wasn't a pointer.