std::stringstream can be used as bytestream?

[pot]

It's very cold.

Anyway, I'm making a program to scan bytecode.
I want to make it can scan both std::istream and std::vector<char>.

So, when it gets vector, it converts the vector to stringstream.
But there is a problem.
After the conversion, the size of stringstream increases one byte
(adding EOF(-1) to the tail).

Ignoring the last byte isn't so difficult,
but I want to know why this happens.
Would you give me some advises.

Here is a sample.

#include <vector>
#include <sstream>
#include <string>

using namespace std;

int main()
{
	// not unsigned for std::string.
	const char binary[]={
		1,2,3,4,5,6,7,8,
		9,0,1,2,3,4,5,6
	};
	
	string str(binary);
	
	vector<char> v;
	stringstream ss;
	
	for (unsigned i=0; i<sizeof(binary)/sizeof(char); ++i) {
		v.push_back(binary[i]);
		ss << binary[i];
	}

		
	cout << sizeof(binary)/sizeof(char) << endl; // 16
	cout << str.size() << endl;                  // 9, but it's ok.
	cout << v.size() << endl;                    // 16
	
	cout << ss.str().size() << endl;             // 16 <- sure?
	
	vector<char> v2;
	while (!ss.eof()) {
		v2.push_back(ss.get());
	}
	cout << v2.size() << endl;	             // 17 <- why?
	cout << (int)v2[v2.size()-1] << endl;        // -1 <- why eof pushed?
	return 0;
}

Thank you.

[Cubbi]

first of all, replace
string str(binary);
by
string str(binary, sizeof binary);

[Cubbi]

And then, replace

while (!ss.eof()) {
    v2.push_back(ss.get());
}

by

for(char ch; ss.get(ch); ) {
    v2.push_back(ch);
}

the "while not eof" construct is (almost) always an error

[pot]

Thank you, Cubbi.

I'll correct them,
although I've written many loops using eof()...

[Cubbi]

I've written many loops using eof()...

Why?

To answer the original "why eof pushed?", in this program, you've iterated through the 16-byte stream "ss" 17 times. On the 17th iteration, ss.get() was unable to read from the stream, so it executed ss.setstate(eofbit) and returned EOF, which you've push_back()'ed into the vector.
After the 17th iteration, ss.eof() returned true (since eofbit was now set), and the loop ended.

[pot]

I've written many loops using eof()...

Why?

I've already written some programs which may cause this problem before.
So I must fix may loops.

I didn't notice iostream's last EOF,
because I usually output these values in character and didn't count them.

I've checked that other istreams returns EOF, too.

Thank you.

[sohguanh]

Can we make this EOF behavoir as sticky? File IO is an often done operation and quite a lot of developers are still testing against the EOF to detect end of file or input. A lot of times it is (almost) always an error.

Thanks.