The well known way of creating an fstream object is:
ifstream fobj(\"myfile.txt\");
ie. using a filename.
You can create a string, and use fread to read and append to it. It's not clean, but you're working with a C interface.
Something like this should work:
FILE * f = popen(...)
const unsigned N=1024;
string total;
while (true) {
vector buf[N];
size_t read = fread((void *)&buf[0], 1, N, f);
if (read) { total.append(buf.begin(), buf.end()); }
if (read < N) { break; }
}
pclose(f);