How to scan file bytes using istreambuf_iterator<unsigned char> iit(f);

Phil Nicolletti posted this code to load a section of a text file given an open fstream, starting and ending points:

Code:

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/// Suggested by Phil Nicolleti : http://www.codeguru.com/forum/showthread.php?t=473898
/// Modified by Mike Pliam August 19, 2014 for single byte file streams.
vector<char> GetBytes(ifstream &f, long ustart, long uend)
{
        vector<char> vb;
        const long nsz = (uend-ustart)/2;
        vb.resize(nsz); //vb = 0x00;
        if(!f.is_open()) { _RPT0(0, "No stream available in GetBytes.\n"); return vb; }

        if(ustart < 0 || uend < ustart) return vb;


        f.clear();
        f.seekg(ustart);

        istreambuf_iterator<char> iit(f);
        //std::istreambuf_iterator<char> iit (std::cin.rdbuf()); // stdin iterator
 
        for(int ul = 0; ul < nsz; ul++)
        {
                vb[ul] = *iit++;
        }

        return vb;

}// GetBytes(ifstream &f, long ustart, long uend)

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But now I want to load a section of bytes (unsigned char) rather than char. Unfortunately, I cannot get to cooperate:

Code:

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istreambuf_iterator<unsigned char> iit(f);

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.

Error is:

Quote:

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error C2664: 'std::istreambuf_iterator<_Elem>::istreambuf_iterator(std::basic_streambuf<_Elem,_Traits> *) throw()' :
cannot convert parameter 1 from 'std::ifstream' to 'std::basic_streambuf<_Elem,_Traits> *'

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I need bytes, not chars. Help appreciated.

Quote:

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Originally Posted by Mike Pliam

I need bytes, not chars.

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char, signed char and unsigned char can all be used to store "bytes", but the latter tends to be the best option when you will do things like bit shifting.

Quote:

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Originally Posted by Mike Pliam

But now I want to load a section of bytes (unsigned char) rather than char. Unfortunately, I cannot get to cooperate:

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You may need to use std::istream_iterator instead of std::istreambuf_iterator, but I'm not sure how that might affect the efficiency. Alternatively, you could switch the std::vector<unsigned char>, but leave it as std::istreambuf_iterator<char> since whether char is signed or unsigned, the conversion to unsigned char will be safe.