Programming :: Check Available Space On A Directory With C++?

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;

[Code]...