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C++ Discussion Thread
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Views: 1136

Feb 25th, 2009

Problem with writing hex values

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Hi everyone,
i wrote this small app and it works fine but it erases everything up to the offset and everything after it.
Anyone knows how to avoid that?

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <fstream>
 
int main()
{
	int hex = 0x75;
	std::ofstream f("sample.exe", std::ios::binary);
	f.seekp(1169, std::ios::beg);
	f.write(reinterpret_cast<const char *>(&hex), 2);
	f.close();
	return 0;
}
#include <iostream>
#include <fstream>

int main()
{
	int hex = 0x75;
	std::ofstream f("sample.exe", std::ios::binary);
	f.seekp(1169, std::ios::beg);
	f.write(reinterpret_cast<const char *>(&hex), 2);
	f.close();
	return 0;
}

regards

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replic

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Feb 25th, 2009

Re: Problem with writing hex values

also use mode std::ios::ate (AT End)

The default mode for ofstream opening is std::ios::trunc, (TRUNCate), which deletes any previous content of the file. ios::ate preserves the file, allows you to move the file pointer anywhere within the current content.

vmanes

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Posting Virtuoso

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Feb 27th, 2009

Re: Problem with writing hex values

It still doesn't work using this code.
It produces the same error again.

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <fstream>
 
int main()
{
      int hex = 0x75;
      std::ofstream f("sample.exe", std::ios::binary | std::ios::ate);
      f.seekp(1169, std::ios::beg);
      f.write(reinterpret_cast<const char *>(&hex), 2);
      f.close();
      return 0;
}
#include <iostream>
#include <fstream>
 
int main()
{
      int hex = 0x75;
      std::ofstream f("sample.exe", std::ios::binary | std::ios::ate);
      f.seekp(1169, std::ios::beg);
      f.write(reinterpret_cast<const char *>(&hex), 2);
      f.close();
      return 0;
}

replic

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since Nov 2008

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Feb 27th, 2009

Re: Problem with writing hex values

To get 'non-destructive writes', open the file specifying also the ios::in mode.

mitrmkar

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Posting Virtuoso

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Mar 1st, 2009

Re: Problem with writing hex values

Yes that did the trick thanks a lot.

replic

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