Referencing Problem

[yoonkwun]

An object of type std::string is to call its size() method and reference the returned variable:

&strIn.size()
or
&(strIn.size())

Why does this code produce this error:

error: lvalue required as unary '&' operand

size() should return a variable of type size_t, which I would think should be able to be referenced like any other variable.

[1yR4jE8b]

No it can't. You would only be able to do that if the size() member function returned a reference to it's size member variable, but it only returns a copy.

The new C++0x standard will ratify this, however.

[rwan]

size_t is equivalent to a number (I can't remember if it was an unsigned int). So, you're taking a reference of a number, which you can't.

You should just use strIn.size ().

[filipe]

@yoonkwun: you'd have nothing to gain by using a reference there. The cost of copying an int or a similar type is slightly smaller than the cost of passing a reference. If you're interested: http://stackoverflow.com/questions/3009543/passing-integers-as-constant-references-versus-copying

[yoonkwun]

My purpose is to write the variable returned by size() to a file. It would've been nice if I could do something like this:

fwrite(&strIn.size(), 4, 1, fileOut);

But I guess I'm left with no choice:

size_t temp = strIn.size();
fwrite(&temp, 4, 1, fileOut);

[filipe]

You could just use streams instead of the C library. It would be as simple as ofs << strIn.size();

[Disch]

except that outputs it as text, and not as binary.

The iostream version of outputting binary also requires a temp var.