MSDN：

GetLogicalDriveStrings

The GetLogicalDriveStrings function fills a buffer with strings that specify valid drives in the system.

获取一个字串，其中包含了当前所有逻辑驱动器的根驱动器路径

DWORD GetLogicalDriveStrings(
  DWORD nBufferLength,  // size of buffer
  LPTSTR lpBuffer       // pointer to buffer for drive strings
);
 

Parameters

nBufferLength

Specifies the maximum size, in characters, of the buffer pointed to by lpBuffer. This size does not include the terminating null character.

缓冲区的大小

lpBuffer

Pointer to a buffer that receives a series of null-terminated strings, one for each valid drive in the system, that end with a second null character. The following example shows the buffer contents with <null> representing the terminating null character.

c:\<null>d:\<null><null> 
用于装载逻辑驱动器名称的字串。每个名字都用一个NULL字符分隔，在最后一个名字后面用两个NULL表示中止（空中止） 例如A:\<null>C:\<null><null>

Return Values

If the function succeeds, the return value is the length, in characters, of the strings copied to the buffer, not including the terminating null character. Note that an ANSI-ASCII null character uses one byte, but a Unicode null character uses two bytes.

If the buffer is not large enough, the return value is greater than nBufferLength. It is the size of the buffer required to hold the drive strings.

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

返回保存所有数据所需要的字节数。应该总是比较返回值与参数cchBuffer的大小。

Remarks

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