Can't Recurse Directories Properly - c++

Question

I am trying to recurse directories in a c++ program I am creating using the QT creator application. For some reason, neither QDir::entryList nor QDirIterator seem to work. Using QDirIterator I can get the second directory down but it goes no further. A similar thing happens when I use QDir::entryList with nested foreach loops. Ultimately, I'd like to get the last directory, which contains no other directories, in a chain of directories.
This is intended to be cross-platform so it cannot be OS specific. I'd also like to avoid lots of switches for different OS' as I'd like to not have to work on it later and simply use it (potentially forever). I have tried foreach loops, while loops, anything I could think of.
QDir Code:
QStringList GetLastSubDirs(QDir baseDirectory) {
QStringList result;
baseDirectory.setFilter( QDir::Dirs|QDir::NoDotAndDotDot );
QStringList nonEmptyDirs(baseDirectory.path());
while (nonEmptyDirs.size() > 0) {
foreach (QString d, nonEmptyDirs) {
QDir sd(d);
foreach (QDir checkingDir, sd.entryList(QDir::Dirs|QDir::NoDotAndDotDot)) {
if (checkingDir.entryList().size() == 0) {
result.append(checkingDir.path());
} else {
nonEmptyDirs.append(checkingDir.path());
}
}
nonEmptyDirs.removeOne(d);
}
}
if (result.size() == 0) {
result = QStringList(baseDirectory.path());
}
return result;
}
};
Here is the QDirIterator code:
class Directories
{
public:
QStringList GetLastSubDirs(QDir baseDirectory) {
QStringList result;
baseDirectory.setFilter( QDir::Dirs|QDir::NoDotAndDotDot );
QDirIterator it(QDir::currentPath() + "/" + baseDirectory.path(), QDirIterator::Subdirectories);
while(it.hasNext()) {
QDir curWorkDir(it.path());
curWorkDir.setFilter( QDir::Dirs|QDir::NoDot|QDir::NoDotDot );
if(curWorkDir.entryList().size() >= 1) {
foreach (QDir d, curWorkDir.entryList()) {
d.setFilter( QDir::Dirs|QDir::NoDot|QDir::NoDotDot );
if (d.entryList().size() <= 0) {
result.append(d.path());
}
}
} else {
result.append(curWorkDir.path());
}
it.next();
}
if (result.size() == 0) {
result = QStringList(baseDirectory.path());
}
return result;
}
};
Debugger Output
1 Directories::GetLastSubDirs main.cpp 56 0x555555559ba9
2 Games::Games main.cpp 80 0x555555559f98
3 __static_initialization_and_destruction_0 main.cpp 104 0x55555555931b
4 _GLOBAL__sub_I_main.cpp(void) main.cpp 120 0x55555555934e
5 __libc_csu_init 0x55555555cd9d
6 __libc_start_main libc-start.c 247 0x7ffff54ed270
7 _start 0x555555558f2a
Disassembler output:
0x555555558f00 31 ed xor %ebp,%ebp
0x555555558f02 <+ 2> 49 89 d1 mov %rdx,%r9
0x555555558f05 <+ 5> 5e pop %rsi
0x555555558f06 <+ 6> 48 89 e2 mov %rsp,%rdx
0x555555558f09 <+ 9> 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
0x555555558f0d <+ 13> 50 push %rax
0x555555558f0e <+ 14> 54 push %rsp
0x555555558f0f <+ 15> 4c 8d 05 aa 3e 00 00 lea 0x3eaa(%rip),%r8 # 0x55555555cdc0 <__libc_csu_fini>
0x555555558f16 <+ 22> 48 8d 0d 33 3e 00 00 lea 0x3e33(%rip),%rcx # 0x55555555cd50 <__libc_csu_init>
0x555555558f1d <+ 29> 48 8d 3d 74 01 00 00 lea 0x174(%rip),%rdi # 0x555555559098 <main(int, char**)>
0x555555558f24 <+ 36> ff 15 c6 70 20 00 callq *0x2070c6(%rip) # 0x55555575fff0
0x555555558f2a <+ 42> f4 hlt
I expect this particular snippet of code to recurse directories until it has cleared any directory that contains other directories. Instead it will only go down one level and stop. For some reason when querying the entryList().size() of these directories it always comes back with 0, even if the directory contains other directories, unless I include . and .. and then it just loops forever because it wasn't intended to handle that.

Answer 1

I don't know why you make it so complicated. The documentation says this:
The QDirIterator class provides an iterator for directory entrylists.
You can use QDirIterator to navigate entries of a directory one at a time. It is similar to QDir::entryList() and QDir::entryInfoList(), but because it lists entries one at a time instead of all at once, it scales better and is more suitable for large directories. It also supports listing directory contents recursively, and following symbolic links. Unlike QDir::entryList(), QDirIterator does not support sorting.
The QDirIterator constructor takes a QDir or a directory as argument. After construction, the iterator is located before the first directory entry. Here's how to iterate over all the entries sequentially:
QDirIterator it("/etc", QDirIterator::Subdirectories);
while (it.hasNext()) {
qDebug() << it.next();
// /etc/.
// /etc/..
// /etc/X11
// /etc/X11/fs
// ...
}
QDirIterator is already recursive when supplying QDirIterator::Subdirectories.

Answer 2

QDir::EntryList returns the names of the child entries, not their full paths. You need to append the name to the parent path to get the full path.
Given a hierarchy:
basedir/
child1/
child2/
grandchild1/
grandchild2/
calling entryList on baseDir will return ["child1", "child2"], not ["basedir/child1", "basedir/child2"]
As I said in the comments: I do not expect this code to work even when you fix that problem. You are modifying nonEmptyDirs inside a foreach loop over nonEmptyDirs. That feels dangerous. It certainly wouldn't work inside a C++11 ranged-for loop. I suggest writing the foreach macro out by hand to check that it will work. In particularly, removing the entry in a list which the current iterator points to, is not going to end well.

Answer 3

From the Qt documentation ... last sentence most important
Qt automatically takes a copy of the container when it enters a foreach loop. If you modify the container as you are iterating, that won't affect the loop. (If you do not modify the container, the copy still takes place, but thanks to implicit sharing copying a container is very fast.)
Since foreach creates a copy of the container, using a non-const reference for the variable does not allow you to modify the original container. It only affects the copy, which is probably not what you want.