如何传递结构给DLL
编号：QA002083
建立日期: 1999年11月24日 最后修改日期：1999年11月24日
所属类别：
李强:
操作系统: windows98
编程工具: pvf6.0
问题: 我在调用一些API（如：SHFileOperation）函数时，需要定义如下的结构：
Private Type SHFILEOPSTRUCT
hwnd As Long
wFunc As Long
pFrom As String
pTo As String
fFlags As Integer fAnyOperationsAborted As Long
hNameMappings As Long
lpszProgressTitle As String
End Type
但上面的结构只在VB、VC里才有，不知在PVF里可否实现此功能。谢谢！
回答:
参考：微软的Knowledge Base的文章：“Q181289 OWTO: Pass Structures to a DLL”，下面是摘要：
SUMMARY
=======
Many DLLs require that the calling program pass a structure. FoxPro can pass by reference a string of the same length as the required structure. Depending on the datatype, some variables need to be converted to the proper format. For instance, DWORD is a low-high format, so any 4-byte values need to be converted to a string in the DWORD format. DLLs may also return values that need to be converted from a string in a low-high format to an integer value.
MORE INFORMATION
================
The Win32 API function GetSystemInfo requires that a pointer to a structure be passed to the function. The following example demonstrates how to make the call then convert the elements of the returned string using the StrToLong function. The LongToStr function to do the reverse is also included.
Copy this code into a program file (.prg) and run the program. This program uses GetSystemInfo to return information about a computer's processor and memory.
The code is listed below:
#DEFINE CR CHR(13)
#DEFINE PROCESSOR_INTEL_386 386
#DEFINE PROCESSOR_INTEL_486 486
#DEFINE PROCESSOR_INTEL_PENTIUM 586
#DEFINE PROCESSOR_MIPS_R4000 4000
#DEFINE PROCESSOR_ALPHA_21064 21064
DECLARE GetSystemInfo IN win32api STRING @SystemInfo
DECLARE GlobalMemoryStatus IN win32api STRING @MemStat
SystemInfo = SPACE(36)
m.stru = LongToStr(32) + REPLICATE(CHR(0), 28)
=GetSystemInfo(@SystemInfo)
=GlobalMemoryStatus(@m.stru)
m.oem_id = StrToLong(LEFT(SystemInfo, 4))
m.page_size = StrToLong(SUBSTR(SystemInfo, 5, 4))
m.minappaddr = StrToLong(SUBSTR(SystemInfo, 9, 4))
m.maxappaddr = StrToLong(SUBSTR(SystemInfo, 13, 4))
m.processormask = StrToLong(SUBSTR(SystemInfo, 17, 4))
m.num_processors = StrToLong(SUBSTR(SystemInfo, 21, 4))
m.processortype = StrToLong(SUBSTR(SystemInfo, 25, 4))
m.processorname = ""
m.memoryload = StrToLong(SUBSTR(m.stru, 5, 4))
m.totalphys = StrToLong(SUBSTR(m.stru, 9, 4))
m.availphys = StrToLong(SUBSTR(m.stru, 13, 4))
m.totalpagefile = StrToLong(SUBSTR(m.stru, 17, 4))
m.availpagefile = StrToLong(SUBSTR(m.stru, 21, 4))
m.totalvirtual = StrToLong(SUBSTR(m.stru, 25, 4))
m.availvirtual = StrToLong(SUBSTR(m.stru, 29, 4))
DO CASE
CASE m.processortype = PROCESSOR_INTEL_386
m.processorname = "INTEL 386"
CASE m.processortype = PROCESSOR_INTEL_486
m.processorname = "INTEL 486"
CASE m.processortype = PROCESSOR_INTEL_PENTIUM
m.processorname = "INTEL Pentium"
CASE m.processortype = PROCESSOR_MIPS_R4000
m.processorname = "MIPS R4000"
CASE m.processortype = PROCESSOR_ALPHA_21064
m.processorname = "ALPHA 21064"
ENDCASE
m.allocationgranularity = StrToLong(SUBSTR(SystemInfo, 29, 4))
m.reserved = StrToLong(SUBSTR(SystemInfo, 33, 4))
=MESSAGEBOX("OEM ID:" + STR(m.oem_id) + CR + ;
"Page Size: " + STR(m.page_size) + CR + ;
"Minimum application address: " + STR(m.minappaddr) + CR +;
"Maximum application address: " + STR(m.maxappaddr) + CR + ;
"Processor mask: " + STR(m.processormask) + CR + ;
"Number of processors: " + STR(m.num_processors) + CR + ;
"Allocation granularity: " + STR(m.allocationgranularity) + CR + ;
"Percent memory in use: " + STR(m.memoryload) + CR + ;
"Bytes of physical memory present: " + STR(m.totalphys) + CR + ;
"Bytes available physical memory: " + STR(m.availphys) + CR + ;
"Bytes of paging file: " + STR(m.totalpagefile) + CR + ;
"Bytes available paging file: " + STR(m.availpagefile) + CR + ;
"Total virtual memory: " + STR(m.totalvirtual) + CR + ;
"Available bytes virtual memory: " + STR(m.availvirtual),0+64+0)
*-- The following function converts a long integer to an ASCII
*-- character representation of the passed value in low-high format.
******************
FUNCTION LongToStr
******************
* Passed : 32-bit non-negative numeric value (lnLongval)
* Returns : ascii character representation of passed value in low-high
* format (lcRetstr)
* Example :
* m.long = "999999"
* m.longstr = long2str(m.long)
PARAMETERS lnLongval
PRIVATE i, lcRetstr
lcRetstr = ""
FOR i = 24 TO 0 STEP -8
lcRetstr = CHR(INT(lnLongval/(2^i))) + lcRetstr
lnLongval = MOD(lnLongval, (2^i))
NEXT
RETURN lcRetstr
*-- The following function converts a string in low-high format to a
*-- long integer.
******************
FUNCTION StrToLong
******************
* Passed: 4-byte character string (lcLongstr) in low-high ASCII format
* Returns: long integer value
* Example:
* m.longstr = "1111"
* m.longval = str2long(m.longstr)
PARAMETERS lcLongstr
PRIVATE i, lnRetval
lnRetval = 0
FOR i = 0 TO 24 STEP 8
lnRetval = lnRetval + (ASC(lcLongstr) * (2^i))
lcLongstr = RIGHT(lcLongstr, LEN(lcLongstr) - 1)
NEXT
RETURN lnRetval
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此问题由李海回答。
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