GlobalAlloc 而不是其他分配方法

Question

在 MSDN 上查看 finding the owner of the given file object 的代码时，程序使用 GlobalAlloc() 将内存分配给 AcctName。由于我是 Win32 API 的新手，我的好奇心使我询问为什么我们使用 GlobalAlloc() 而不是其他分配方法。如果存在其他更好的分配方法，如何在给定的代码中使用它们？

#include <stdio.h>
#include <windows.h>
#include <tchar.h>
#include "accctrl.h"
#include "aclapi.h"
#pragma comment(lib, "advapi32.lib")

int main(void)
{
DWORD dwRtnCode = 0;
PSID pSidOwner = NULL;
BOOL bRtnBool = TRUE;
LPTSTR AcctName = NULL;
LPTSTR DomainName = NULL;
DWORD dwAcctName = 1, dwDomainName = 1;
SID_NAME_USE eUse = SidTypeUnknown;
HANDLE hFile;
PSECURITY_DESCRIPTOR pSD = NULL;


// Get the handle of the file object.
hFile = CreateFile(
                  TEXT("myfile.txt"),
                  GENERIC_READ,
                  FILE_SHARE_READ,
                  NULL,
                  OPEN_EXISTING,
                  FILE_ATTRIBUTE_NORMAL,
                  NULL);

// Check GetLastError for CreateFile error code.
if (hFile == INVALID_HANDLE_VALUE) {
          DWORD dwErrorCode = 0;

          dwErrorCode = GetLastError();
          _tprintf(TEXT("CreateFile error = %d\n"), dwErrorCode);
          return -1;
}



// Get the owner SID of the file.
dwRtnCode = GetSecurityInfo(
                  hFile,
                  SE_FILE_OBJECT,
                  OWNER_SECURITY_INFORMATION,
                  &pSidOwner,
                  NULL,
                  NULL,
                  NULL,
                  &pSD);

// Check GetLastError for GetSecurityInfo error condition.
if (dwRtnCode != ERROR_SUCCESS) {
          DWORD dwErrorCode = 0;

          dwErrorCode = GetLastError();
          _tprintf(TEXT("GetSecurityInfo error = %d\n"), dwErrorCode);
          return -1;
}

// First call to LookupAccountSid to get the buffer sizes.
bRtnBool = LookupAccountSid(
                  NULL,           // local computer
                  pSidOwner,
                  AcctName,
                  (LPDWORD)&dwAcctName,
                  DomainName,
                  (LPDWORD)&dwDomainName,
                  &eUse);

// Reallocate memory for the buffers.
AcctName = (LPTSTR)GlobalAlloc(
          GMEM_FIXED,
          dwAcctName);

// Check GetLastError for GlobalAlloc error condition.
if (AcctName == NULL) {
          DWORD dwErrorCode = 0;

          dwErrorCode = GetLastError();
          _tprintf(TEXT("GlobalAlloc error = %d\n"), dwErrorCode);
          return -1;
}

    DomainName = (LPTSTR)GlobalAlloc(
           GMEM_FIXED,
           dwDomainName);

    // Check GetLastError for GlobalAlloc error condition.
    if (DomainName == NULL) {
          DWORD dwErrorCode = 0;

          dwErrorCode = GetLastError();
          _tprintf(TEXT("GlobalAlloc error = %d\n"), dwErrorCode);
          return -1;

    }

    // Second call to LookupAccountSid to get the account name.
    bRtnBool = LookupAccountSid(
          NULL,                   // name of local or remote computer
          pSidOwner,              // security identifier
          AcctName,               // account name buffer
          (LPDWORD)&dwAcctName,   // size of account name buffer 
          DomainName,             // domain name
          (LPDWORD)&dwDomainName, // size of domain name buffer
          &eUse);                 // SID type

    // Check GetLastError for LookupAccountSid error condition.
    if (bRtnBool == FALSE) {
          DWORD dwErrorCode = 0;

          dwErrorCode = GetLastError();

          if (dwErrorCode == ERROR_NONE_MAPPED)
              _tprintf(TEXT
                  ("Account owner not found for specified SID.\n"));
          else 
              _tprintf(TEXT("Error in LookupAccountSid.\n"));
          return -1;

    } else if (bRtnBool == TRUE) 

        // Print the account name.
        _tprintf(TEXT("Account owner = %s\n"), AcctName);

    return 0;
}

Answer 1

有关 Microsoft Windows 中当前存在的不同内存分配函数的概述，请参阅 this Microsoft documentation page。

基本上，GlobalAlloc 是 Microsoft 博主 Raymond Chen 16-bit Windows. In 32-bit and 64-bit Windows, there is no longer a distinction between GlobalAlloc and LocalAlloc, as modern operating systems use a flat memory model. If you are interested in what significance these functions had in 16-bit Windows, you can read this article 的残余。

如 offical documentation of the function GlobalAlloc 中所述，此函数通常不应在现代 32 位或 64 位应用程序中使用，除非文档明确告诉您这样做。

自 official documentation on the function LookupAccountSid does not specify that any of the passed buffers must have been allocated with GlobalAlloc, there is no reason to use this function. It would be more appropriate to for example use the function HeapAlloc 以来，此函数的开销低于 GlobalAlloc。或者，您可以使用普通的 C++ 内存分配（例如 new 或 std::vector），这取决于实现，可能会间接调用函数 HeapAlloc。

Answer 2

谢谢大家。我刚刚使用 malloc.

修改了我的代码

    AccountBuff = (LPSTR)malloc(AccountBufflength * sizeof(LPSTR));
    DomainBuff = (LPSTR)malloc(DomainBufflength * sizeof(LPSTR));

GlobalAlloc 而不是其他分配方法

GlobalAlloc instead of other allocation method

c++

winapi

memory-management

heap-memory