原型：DWORD GetLogicalDrivers (void);

说明：函数返回值是一个long型，将其用二进制显示时，其中第0位表示A盘，第1位表示B盘，当某位为1时说明存在这个盘，即00000011表示有A盘和B盘。

看这个例子：

#include <windows.h>
int main()
{
DWORD dw;
TCHAR TC1[50],TC2[50];

dw = GetLogicalDrives();
wsprintf(TC1,"%ld",dw);
MessageBox(NULL,TC1,"十进制",MB_OK);

_itoa(dw,TC2,2);
MessageBox(NULL,TC2,"十进制",MB_OK);
return 0;
}

 一目了然哈

改下：

#include <windows.h>
int main()
{
DWORD dw;
TCHAR TC[50];
    int count = 0;
dw = GetLogicalDrives();
while(dw != 0)
{
   if( (dw&1) != 0)
   {
       count++;
   }
   dw >>= 1;
}
wsprintf(TC,"驱动器个数：%d",count);
MessageBox(NULL,TC,"我插了U盘的",MB_OK);
return 0;
}

判断某个盘符是否存在：

#include <windows.h>
int main()
{
    DWORD dw;
    TCHAR TC[50];
    dw = GetLogicalDrives();
    char ch;
    ch = 'Q';
    int n = ch - 'A';

    if( (dw != 0) && (dw >>= n) != 0 )
    {
        wsprintf(TC,"%c 盘 存 在",ch);
    }
    else
    {
        wsprintf(TC,"%c 盘 不 存 在",ch);
    }

    MessageBox(NULL,TC,"判断 该盘 是否存在",MB_OK);
    return 0;
}

MSDN:

GetLogicalDrives

The GetLogicalDrives function retrieves a bitmask representing the currently available disk drives.

DWORD GetLogicalDrives(VOID);

Parameters

This function has no parameters.

Return Values

If the function succeeds, the return value is a bitmask representing the currently available disk drives. Bit position 0 (the least-significant bit) is drive A, bit position 1 is drive B, bit position 2 is drive
C, and so on.

If the function fails, the return value is zero. To get extended error information, call
GetLastError.

Remarks

Windows XP: This function returns a concatenation of the logical disks in the Global and Local MS-DOS Device namespaces. If a logical disk exists in both namespaces, this function will return the
entry in the Local MS-DOS Devices namespace.

For more information on the Global and Local MS-DOS Device namespaces and changes to the accessibility of MS-DOS device names in Windows XP, refer to
MS-DOS Device Names.

Requirements

Windows NT/2000/XP:
Included in Windows NT 3.1 and later.
Windows 95/98/Me: Included in Windows 95 and later.
Header: Declared in Winbase.h; include Windows.h.
Library: Use Kernel32.lib.