Check available space on a directory with c++

Lobinho · 09-23-2010, 02:30 PM

Hi,

I'm using c++ and Ubuntu and I need to write/copy some files to a directory chosen by the user of my system (the user can save it on any folder of any disk of the pc or other usb device). Before I do it, I need to know if there's space available on the disk. I cannot only check the result of write() function, the validation must be executed before I start to save or copy.

I was trying to use statvsf structure, but I only have the complete filepath (/home/lobinho/myDocs/), not the disk path. The statvfs() function only works with disk path (i.e. /media/KINGSTON ).

The source of my function:

Code:

int MyClass::availableSpace(string dst, ulong* availableSize) {
    int result = ERROR;
    try {
        struct statvfs devData;
        memset(&devData, 0, sizeof (struct statvfs));
        if ((statvfs(dst.c_str(), &devData)) >= 0) {
            if (availableSize != NULL) {
                //I don't know if it's right, but I'll set availableSize only if the available size doesn't pass the ulong limit.
                if (devData.f_bfree * devData.f_bsize > 4294967295UL) {
                    *availableSize = 4294967295UL;
                } else { 
                    *availableSize = devData.f_bfree * devData.f_bsize;
                }
            }
            result = OK;
        }
    } catch (...) {

    }
    return result;
}

This function works perfectly with the disk path.

Is there any other function that could help me?
I've tried search references on cplusplus, google, but no answer until now... :/

thanks in advance!

gothrog · 09-23-2010, 10:58 PM

Ahhh.... can't you use an Operating System call to check the used and available space. I forget the exact commands but I know they are there.

Lobinho · 09-24-2010, 06:41 AM

Thanks for your response gothrog.

There's "du" and "df".
du works showing the size of some file
df shows the available space on the disk (like statvfs())

I think both command can't help me.

Nylex · 09-25-2010, 06:52 AM

Why can't you use du or df? Also, why are you doing this in C++ rather than a shell script?

theNbomr · 09-25-2010, 10:23 AM

It seems to me, you need the functionality of df. You can use it directly, by launching it as a child process, capturing and parsing its output to determine the amount of free space on the appropriate filesystem. Or, you could acquire the source code for df, and use the methods found in it to build the functionality into your program.
You can read & parse /proc/mounts to divine on which filesystem the target file would be written. There may be other useful data in the /proc virtual filesystem, although I was unable to locate anything after a quick scan.

--- rod.