Presently, I set the value of a std::vector
from an std::ostringstream
as follows:
void
foo(std::vector &am
Copy from a stream iterator to a back insert iterator:
std::istream src;
std::vector<char> dst;
std::copy(std::istream_iterator<char>(src), std::istream_iterator<char>(), std::back_inserter(dst));
The istream_iterator uses formatted conversion (i.e. skips whitespace), so this may not be what you want. I'm not sure what your goal is.
Your method invokes undefined behaviour. stream.str()
returns a string by-value, aka a temporary string. You take the begin
iterator of one temporary and the end
iterator of the other, creating an invalid range.
One method to convert a stream to a container is to use the common iterator interface:
#include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <iterator>
int main(){
std::stringstream src("....");
std::vector<char> dest;
// for a bit of efficiency
std::streampos beg = src.tellg();
src.seekg(0, std::ios_base::end);
std::streampos end = src.tellg();
src.seekg(0, std::ios_base::beg);
dest.reserve(end - beg);
dest.assign(std::istreambuf_iterator<char>(src), std::istreambuf_iterator<char>());
std::copy(dest.begin(), dest.end(), std::ostream_iterator<char>(std::cout));
}
Live example on Ideone.
Another method would be to cache the returned std::string
object:
std::string const& s = stream.str();
data.reserve(s.size());
data.assign(s.begin(), s.end());
if there is a more efficient way
You may want to call reserve
on your data
and use the range insert
member directly on data
instead of using a copy-assignment. The thing about vector
s that you need to remember is that every node may potentially increase the size (and relocate all elements). So, you're better off allocating the memory in one go (if you know how many objects you will be storing -- which you do know here) and leverage this fact.
As pointed out in comments, your code is incorrect due to the two calls to str()
. In order to improve efficiency you can avoid creating a temporary vector
, like this:
void foo(std::vector<char> &data, std::stringstream &stream) {
const std::string& str = stream.str();
data.assign( str.begin(), str.end() );
}
You can also avoid the std::string
by using std::istreambuf_iterator
s:
void foo(std::vector<char> &data, std::stringstream &stream) {
data.assign(
std::istreambuf_iterator<char>( stream ), std::istreambuf_iterator<char>()
);
}
but given that those are input iterators, the vector
has no chance to know how much data will be assigned and could perform a bit worse, as it cannot reserve
enough space to avoid reallocations.