Question

Using the code below in order to get names of my drives:

const DWORD buffer_length = sizeof(DWORD)*CHAR_BIT;
WCHAR buffer[buffer_length] = {0};
GetLogicalDriveStrings(buffer_length,buffer);
std::set<wchar_t> drives_letters;
for(auto e : buffer)
{
    drives_letters.insert(e);
}

• 跟踪产出结果(绕过驱动力-字母):

: //what on earth is this?  
C 
D 
E 
F 
G 
I 
 //and what on earth is this?

Answer 1

GetLogicalDriveStrings returns strings in the form C:. This can be inferred from this documentation passage:

Each string in the buffer may be used wherever a root directory is required, such as for the GetDriveType and GetDiskFreeSpace functions.

Since you are putting these characters into a set, which disallows duplicates, you end up with all the different drive letters plus one copy of a double colon and a backslash. And the reason that the colon prints first and the backslash last is that std::set is inherently ordered, so the ASCII codes of each character decide.

Answer 2

Your for loop is wrong. You are assuming that GetLogicalDriveStrings() returns individual drive letters only, and that is not the case (if you want that, use GetLogicalDrives() instead). It returns paths to drive root folders, and as such you need to change your for loop the following:

const DWORD buffer_length = 104; // can return drive paths A: - Z:
WCHAR buffer[buffer_length+1] = {0}; // room for null terminator

GetLogicalDriveStrings(buffer_length, buffer);
std::set<wchar_t> drives_letters;
for(wchar_t *drive = buffer; *drive != 0; drive += 4)
{
    drives_letters.insert(*drive);
}

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