Find and replace a text string in a binary file

[wey97]

I have code to read the file and print it out. I need to search for a string and replace it so I figured it would be better to do it in C++.

	unsigned char ch;
	int linecounter=0;
	FILE *in;
	in = fopen("myfile.bin","rb");
	if(ferror(in) ){
		perror("Error opening input file:");
		exit(1);
	}
	while (!feof(in) ){
		if(  fread(&ch,sizeof(ch),1,in) ==1){
			/* do stuff with the character you just read */
			printf("%c",ch);
			linecounter++;
			if ( !(linecounter%30) ) 
				printf("\n");
		}
	}
	fclose(in);

Can this be done in C++ to get the data in a string?

[CornedBee]

It can be done, but I recommend you use the file streams and strings to do that. Read a bit about the C++ standard library.

[wey97]

I have it in a buffer now but null characters are causing trouble.

#include <fstream>
#include <iostream>
#include <string>

using namespace std;

int main()
{
	ifstream ifs("C:\\test.lnk", ios::in | ios::binary);

	char buffer[1024];
	ifs.read(buffer, 1024);

	for(int i = 0; i < 1024; i++)
	{
		cout << buffer[i];
	}
}

That prints everything but if I do

string str = buffer;
cout << str << endl;
cout << str.length() << endl;

then obviously I only get one character printed and str.length() is 1

[CornedBee]

Well, strings are for character data, not binary data. The file seems to contain binary data, no? Or why does it contain so many NULs, why do you open it as binary?

You can use a vector or a deque for binary data.

[wey97]

Well it's a shortcut (.lnk) file and there is a path string nested in it something like 'C : \ f o l d e r \' etc.

where the spaces are nulls. I just put it in a char buffer so I could visually see what I am looking to replace and hopefully search it as string.

[CornedBee]

Hmmm...
I think you should read it all into a binary buffer, then parse the binary data to find the place where the string is. Then check only that string. lnk files have a structured format, try wotsit.org. Search for lnk there and look at the document in the middle link.

[wey97]

The link was helpful.

Here's the code if anybody needs it.

#include <windows.h>
#include <shobjidl.h>
#include <shlguid.h>
#include <iostream>
#include <string>
using namespace std;

typedef unsigned int uint;

bool StringFind(string sSearchIn, string sSearchFor, uint &nPos)
{
	uint nTemp = (uint)sSearchIn.find(sSearchFor);

	if(nTemp < sSearchIn.length())
	{
		nPos = nTemp;
		return true;
	}

	return false;
}


bool Replace(string &sLine, string sReplaceWhat, string sReplaceWith)
{
	uint nPos = 0;
	uint i = 0;

	while(StringFind(sLine, sReplaceWhat, nPos))
	{
		sLine = sLine.replace(nPos, sReplaceWhat.length(), sReplaceWith);
		i++;
	}

	if(i)return true; 
	
	return false;
}

void ModArguments(string sFileLink, string sFind, string sReplace)
{
	HRESULT hres; 
	IShellLink *psl;
	IPersistFile *ppf;

	WCHAR szTextW[1024]; 
	TCHAR szText[1024];
	string str;

	CoInitialize(NULL);

	// Get a pointer to the IShellLink interface. 
	hres = CoCreateInstance(CLSID_ShellLink, NULL, CLSCTX_INPROC_SERVER, 
		IID_IShellLink, (LPVOID*)&psl); 

	MultiByteToWideChar(0, 0, sFileLink.c_str(), -1, szTextW, 1024);

	psl->QueryInterface(IID_IPersistFile, (LPVOID*)&ppf);

	ppf->Load(szTextW, STGM_READ);

	psl->GetArguments(szText, 1024);
	str = szText;

	Replace(str, sFind, sReplace);

	psl->SetArguments(str.c_str());

	ppf->Save(szTextW, TRUE);

	ppf->Release();
	psl->Release();

	CoUninitialize();
}


int main()
{
	ModArguments("C:\\test.lnk", "OldArgs", "NewArgs");
	system("pause");
}