How to make istringstream more efficient?

Question

#include <sstream>

using namespace std;

const char* GetHugeString();

int main()
{
    const char* p = GetHugeString();

    //
    // Below will copy the huge string into a std::string object!
    // 
    istringstream sstrm{p}; 

    return {};
}

istringstream doesn't need a copy of the huge string; a null-terminated string pointer is enough. But istringstream's ctor only take std::string, rather than std::string_view(c++1z only), as its argument.

Is there a work-around to make std::istringstream more efficient in such a case?

Answer 1

You can simply assign the buffer used internally in the istringstream:

istringstream stream;
stream.rdbuf()->pubsetbuf(p, strlen(p));

This does not copy the string. Do note that pubsetbuf() wants char* not const char*, but it doesn't actually modify the string, so you might const_cast your C string pointer before passing it.