如何取消设置 std::cout 精度？

Question

cout.precision(m);

cout << "specified number of digits pi_float = " << a_0 << endl;

In my further computation when I try to print pi with double precision, only m digits are printed. How do I unset std::cout.precision ?

Answer 1

Typically you just set it to whatever you need when you need it, but if you really do want to restore the previous settings you can save and reload it like this:

std::streamsize prev_precision = std::cout.precision(); // save old precision
std::cout.precision(m);
// ... use the stream for whatever ...
std::cout.precision(prev_precision); // restore old precision

You can do this for the other format settings as well (width, fill, scientific notation, boolalpha, etc.).

I have an opensource github project that does just that using RAII if you want a pre-packaged solution covering everything (or just example code to do it).

Answer 2

Store it and restore it

auto p = std::cout.precision(m); cout << "specified numbr of digits pi_float = " << a_0 << endl;
std::cout.precision(p);