Question

以下代码显示DNS客户端中的缓存域名。有人可以帮我找到内存泄漏点击 int stat = DnsGetCacheDataTable（pEntry）; 行吗？
PS：请在编译代码时使用DNSAPI.lib。

#include "stdafx.h"
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <WinDNS.h>
#include <stdarg.h>
typedef struct _DNS_CACHE_ENTRY {
    struct _DNS_CACHE_ENTRY* pNext; // Pointer to next entry
    PWSTR pszName; // DNS Record Name
    unsigned short wType; // DNS Record Type
    unsigned short wDataLength; // Not referenced
    unsigned long dwFlags; // DNS Record FlagsB
} DNSCACHEENTRY, *PDNSCACHEENTRY;

typedef int(WINAPI *DNS_GET_CACHE_DATA_TABLE)(PDNSCACHEENTRY);
void UpdateDNS(void)
{

    PDNSCACHEENTRY pEntry = (PDNSCACHEENTRY) malloc(sizeof(DNSCACHEENTRY));
    // Loading DLL
    HINSTANCE hLib = LoadLibrary(TEXT("DNSAPI.dll"));
    // Get function address
    DNS_GET_CACHE_DATA_TABLE DnsGetCacheDataTable = (DNS_GET_CACHE_DATA_TABLE) GetProcAddress(hLib, "DnsGetCacheDataTable");
    int stat = DnsGetCacheDataTable(pEntry);
    printf("stat = %d\n", stat);
    pEntry = pEntry->pNext;
    while (pEntry) {
        wprintf(L"%s : %d \n", (pEntry->pszName), (pEntry->wType));
        pEntry = pEntry->pNext;
    }
    free(pEntry);
}

int main(int argc, char **argv) {

    while (TRUE)
    {
        Sleep(100);
        UpdateDNS();
    }   
    return 0;
}

Answer 1

此代码存在一些问题。

考虑到您在开始时调用LoadLibrary而未在结束时调用FreeLibrary。虽然技术上不是内存泄漏，但它可能不是最明智的想法......

考虑到在循环之前直接转到pEntry->pNext ，您正在跳过条目。当您分配malloc返回的值时，您的内存泄漏发生在同一行代码中：

PDNSCACHEENTRY pEntry = (PDNSCACHEENTRY) malloc(sizeof(DNSCACHEENTRY)); /* ... */ pEntry = pEntry->pNext;

你甚至不需要malloc，但更糟糕的是，你应该只free malloc个free(pEntry);返回的值，这会导致错误：

malloc

事实上，您不仅不需要free（或DnsRecordListFree），而且您需要的是PDNS_RECORD entry; HINSTANCE hLib = LoadLibrary(TEXT("DNSAPI.dll")); DNS_GET_CACHE_DATA_TABLE DnsGetCacheDataTable = (DNS_GET_CACHE_DATA_TABLE) GetProcAddress(hLib, "DnsGetCacheDataTable"); int stat = DnsGetCacheDataTable(&entry); printf("stat = %d\n", stat); for (DNSCACHEENTRY *pTemp = &entry; pTemp; pTemp = pTemp->pNext) { wprintf(L"%s : %d \n", pTemp->pszName, pTemp->wType); } DnsRecordListFree(entry, DnsFreeRecordList);。

以下是您的代码应该是什么样子：

- (void)itemClicked:(id)sender { NSAlert * alert = [NSAlert alertWithMessageText:@"Toggle Acknowledge" defaultButton:@"Gotcha!" alternateButton:nil otherButton:nil informativeTextWithFormat:@"NSStatusItem was clicked"] [alert runModal] }

Answer 2

尝试使用Deleaker，因为乍一看代码看起来很好：

然后开始调试......当然！你没有原始的pEntry而是修改过的。

这里是更正后的代码：

void UpdateDNS(void)
{

    PDNSCACHEENTRY pEntry = (PDNSCACHEENTRY) malloc(sizeof(DNSCACHEENTRY) + 0x10000);
    PDNSCACHEENTRY pFirstEntry = pEntry;
    // Loading DLL
    HINSTANCE hLib = LoadLibrary(TEXT("DNSAPI.dll"));
    // Get function address
    DNS_GET_CACHE_DATA_TABLE DnsGetCacheDataTable = (DNS_GET_CACHE_DATA_TABLE) GetProcAddress(hLib, "DnsGetCacheDataTable");
    int stat = DnsGetCacheDataTable(pEntry);
    printf("stat = %d\n", stat);
    pEntry = pEntry->pNext;
    while (pEntry) {
        wprintf(L"%s : %d \n", (pEntry->pszName), (pEntry->wType));
        pEntry = pEntry->pNext;
    }
    free(pFirstEntry);
}

更新：事实上，您不需要分配任何内存，因为DnsGetCacheDataTable会自行分配。尝试使用DnsRecordListFree释放内存，但似乎它不起作用。仍有泄漏：

最后我得到了不会泄漏的代码：

typedef int(WINAPI *DNS_GET_CACHE_DATA_TABLE)(PDNSCACHEENTRY*);

typedef void (WINAPI *P_DnsApiFree)(PVOID pData);

void UpdateDNS(void)
{
    PDNSCACHEENTRY pEntry = NULL;
    // Loading DLL
    HINSTANCE hLib = LoadLibrary(TEXT("DNSAPI.dll"));
    // Get function address
    DNS_GET_CACHE_DATA_TABLE DnsGetCacheDataTable = (DNS_GET_CACHE_DATA_TABLE)GetProcAddress(hLib, "DnsGetCacheDataTable");
    P_DnsApiFree pDnsApiFree = (P_DnsApiFree)GetProcAddress(hLib, "DnsApiFree");
    int stat = DnsGetCacheDataTable(&pEntry);
    PVOID pFirstEntry = pEntry;
    printf("stat = %d\n", stat);
    pEntry = pEntry->pNext;
    while (pEntry) {
        wprintf(L"%s : %d \n", (pEntry->pszName), (pEntry->wType));
        pDnsApiFree(pEntry->pszName);
        PVOID p = pEntry;
        pEntry = pEntry->pNext;
        pDnsApiFree(p);
    }
}

使用DnsGetCacheDataTable时内存泄漏

2 个答案: