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convert to hexadecimal

I am trying to understand how the runtime converts this to hex

	std::stringstream s;
        s << std::hex;    
	int i = 0;
        s << std::setw(2) << std::setfill('0') << (unsigned int)(unsigned char)a[i];      // WORKS
        s << std::setw(2) << std::setfill('0') << (unsigned int)a[i];     // DOES NOT WORK

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1. Why do we need this line
s << std::hex;

2) Why does it not work without (unsigned char)

kaufmed

It's a stream manipulator. It coerces the stream to read its data as hexadecimal (where as the default is decimal). You could certainly read the data as a string first, and then do the conversion to hexadecimal value, but this would take a bit more code.

As to why it does not work without (unsigned char), what is the type of your a array?

perlperl

ASKER

The array was void* and passed to this function as const char*

jkr

You could use a 'unsigned int*' cast since it is an array, e.g.

        s << std::setw(2) << std::setfill('0') << ((unsigned int*)a)[i];

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perlperl

ASKER

Thanks jkr. that works too
but I am trying to understand my solution as why
this works (unsigned int)(unsigned char)
and why this not (unsigned int)a

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jkr

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SOLUTION

sarabande

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