1

I can copy some ostringstream into a new char array like this:

std::ostringstream stream;
...

std::string str = stream.str();
size_t size = str.size();

char *target = new char[size];
memcpy(target,str.c_str(),size);

How about the performance? Is there a way to copy the data directly to the array Buffer?

I think it will look like:

size_t size = str.tellp();
char *target = new char[size];
stream.copyTo(target,size); //??
Improve this question
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  • 4
    You can always use the std::string directly. You don't have to copy out of it to use it as a C string (at least in C++11, where it has guaranteed contiguous storage). Commented Dec 12, 2017 at 16:53
  • The would be fine. But I need an char array (created with new char[]) in an other function. Commented Dec 12, 2017 at 17:02
  • 1
    A std::stringessentially already contains that. There's a good answer on how to get at it for modification. It also turns out that C++17 added a non-const version of data() to give direct write access. Commented Dec 12, 2017 at 17:15
  • 1
    If you want to avoid any copying at all, you have to get access to the array that gets used by the stream buffer. A possible approach would be implementing a custom streambuffer and giving that one to the stream, like being done here. Commented Dec 12, 2017 at 17:17
  • As far as array-backed streams go, there's std::strstream, which is deprecated, and std::spanstream, which progressed to LWG at the last meeting, so it might be in C++20. Commented Dec 12, 2017 at 17:31
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