istrstream::istrstream

explicit istrstream(const char *s);
explicit istrstream(char *s);
istrstream(const char *s, streamsize n);
istrstream(char *s, streamsize n);

All the constructors initialize the base class by calling istream(sb), where sb is the stored object of class strstreambuf. The first two constructors also initialize sb by calling strstreambuf((const char *)s, 0). The remaining two constructors instead call strstreambuf((const char *)s, n).