Re: seeking within ostringstream's
On Sep 13, 7:05 pm, Adrian <n...@bluedreamer.com> wrote:
What is a stringsteam supposed to do when you seek past the end of
existing buffer. I can seek past the end of a file stream (my
implementation fills the space will nulls but I cannot find if this is
guaranteed either)
I can't find anything really specifying it either, but I suspect
that it's undefined behavior (or unspecified). It also depends
on whether you are using the two argument form of seek, or the
one argument form. (With the one argument form, it's actually
impossible to obtain a position which you haven't already
visited without involving undefined or unspecified behavior.
With the possible exception of start of file.)
Logically, one might say that a good implementation would
generate an error on an attempt to seek beyond end of file, but
in practice, this would have significant run-time cost on some
systems.
Below code fails for a stringstream. Any good ways of dealing with
this.
Reason for doing this is that I am modify old C code for
screen output that positions fields based on a row. I wanted
to use a stringstream and just seek to the correct place.
I have tried basically filling the stream with X spaces first.
But then I am never sure there is enough space.
#include <iostream>
#include <sstream>
#include <fstream>
int main(int argc, char *argv[])
{
std::ofstream out("test.txt");
out.seekp(500);
The above line is not even guaranteed to compile, much less do
anything useful.
out << "some text\n";
std::ostringstream out2;
out2.seekp(500);
And the same holds true here.
out2 << "some text\n";
if(!out2)
{
std::cout << "bad out2\n";
}
return 0;
}
I'm not too sure what you're doing, but it sounds like what you
want is something like std::string or std::vector<char>, using
resize( ' ' ) as needed.
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