C++(真的)安全标准字符串搜索？

Question

缓冲区溢出问题是众所周知的.因此,我们有幸使用标准库函数,如wcscat_s().微软的好心人已经创建了类似的安全字符串函数,如StringCbCat().

但我有一个问题,我需要搜索一些字符串的内存.标准库函数:

wcsstr( wchar_t* pMem, wchar_t* pStr ) 

看起来很棒,但是...有时我的记忆包含垃圾,有时候是字符串.当它是垃圾时,我有时会运行已分配的内存页面,[=访问冲突].我可以写自己的功能是的.但我的问题是,是否有任何"标准"功能来进行安全字符串搜索,例如:

"wcsstr_s( wchar_t* pMem, size_t uiSize, wchar_t* pStr )" ?

感谢名单

[编辑] 感谢Charles Bailey对我的问题的完美回答.感谢其他人的努力.

对于那些怀疑我的场景的理智的人:是的,当然,在我的记忆中永远不会有垃圾是好的.但我可以想象出现这种情况的几种情况.在我的特殊情况下,它是逆向工程,而我正在处理的内存实际上不是"我的记忆",它属于另一个我无法控制的过程.

(另一个假设场景可能是一个棘手的调试情况,需要跟踪损坏的内存.)

Answer 1

可能不是你想要的答案,但也许这里最好的解决方案是正确初始化你的字符串和指针.如果你的记忆包含垃圾,为什么不做体面的事情并设置

yourString[0] = '\0';

如果它真的只是一个缓冲区的任意位,你可能最好使用像memcmp这样的东西并沿着N字符滑动内存缓冲区的指针(N你感兴趣的字符数减去你要比较的字符串的长度) ).这可能不是最有效的实现,但应该是一个我应该考虑的相当强大的方法.

[编辑]你的问题引起了我的兴趣,足以做一些实验.鉴于您似乎正在寻找更多C风格的答案,这里有一小段代码我想出来详细说明我的memcmp建议:

// SearchingMemoryForStrings.cpp : Defines the entry point for a win32 consol application
// Purpose : Demonstrates a way to search a section of memory for a particular string
//

#include <stdio.h>
#include <string.h>

#define VALUE_NOT_FOUND (-1)

int FindStringInBuffer( const char* pMemBuffer, const size_t& bufferSizeInBytes, const char* pStrToFind )
{
    int stringFound = VALUE_NOT_FOUND; // Return value which will be >= 0 if we find the string we're after
    const char* pMemToMatch = NULL; // An offset pointer to part of 'pMemBuffer' which we'll feed to memcmp to find 'pStrToFind'

    // Set up some constants we'll use while searching
    size_t lenOfStrToFind = strlen( pStrToFind );
    size_t lastSearchablePosition = bufferSizeInBytes - lenOfStrToFind;

    // Search the memory buffer, shifting one character at a time for 'pStrToFind'
    for( size_t i = 0; i <= lastSearchablePosition; i++ ) {
        pMemToMatch = &pMemBuffer[i];
        if( memcmp(pMemToMatch, pStrToFind, lenOfStrToFind) == 0 ) {
            // We found the string we're looking for
            stringFound = i;
            break;
        }
    }

    return stringFound;
}

void ReportResult( int returnVal, const char* stringToFind )
{
    if( returnVal == VALUE_NOT_FOUND ) {
        // Fail!
        printf("Error, failed to find '%s' - search function returned %d\n", stringToFind, returnVal );
    }
    else {
        // Win!
        printf("Success, found '%s' at index %d\n", stringToFind, returnVal );
    }
}

void FindAndReport( const char* pMemBuffer, const size_t& bufferSizeInBytes, const char* pStrToFind )
{
    int result = FindStringInBuffer( pMemBuffer, bufferSizeInBytes, pStrToFind );
    ReportResult( result, pStrToFind );
}

int main( int argc, char* argv[] )
{
    const int SIZE_OF_BUFFER = 1024; // Some aribitrary buffer size
    char some_memory[SIZE_OF_BUFFER]; // The buffer of randomly assigned memory to look for our string
    const char* stringToFind = "This test should pass";
    const char* stringYouWontFind = "This test should fail";

    FindAndReport( some_memory, SIZE_OF_BUFFER, stringYouWontFind ); // Should fail gracefully

    // Set the end of the buffer to the string we're looking for
    memcpy( &some_memory[SIZE_OF_BUFFER-strlen(stringToFind)], stringToFind, strlen(stringToFind) );

    FindAndReport( some_memory, SIZE_OF_BUFFER, stringToFind ); // Should succeed this time and report an index of 1003

    // Try adding at some arbitrary position
    memcpy( &some_memory[100], stringToFind, strlen(stringToFind) );

    FindAndReport( some_memory, SIZE_OF_BUFFER, stringToFind ); // Should still succeed but report the offset as 100

    FindAndReport( some_memory, SIZE_OF_BUFFER, stringYouWontFind ); // Should still fail


    return 0;
}

该片段在Visual Studio 2008下编译为Win32控制台应用程序.给我以下内容:

Error, failed to find 'This test should fail' - search function returned -1
Success, found 'This test should pass' at index 1003
Success, found 'This test should pass' at index 100
Error, failed to find 'This test should fail' - search function returned -1

该FindStringInBuffer功能是你想要的,如果你需要处理宽字符,你需要做一些转换,但这至少应该给你一些你可以继续的想法.如果你想出一个wchar版本,我会有兴趣看看解决方案是什么样的(我自己没有处理过它们).