Correctly pad negative integers with zeros with std::cout

问题

I found this question already asked, but the answer everybody gives is

std::cout << std::setw(5) << std::setfill('0') << value << std::endl;

which is fine for positive numbers, but with -5, it prints:

000-5

Is there a way to make it print -0005 or to force cout to always print at least 5 digits (which would result in -00005) as we can do with printf?

回答1:

std::cout << std::setw(5) << std::setfill('0') << std::internal << -5 << '\n';
//                                                     ^^^^^^^^

Output:

-0005

std::internal

Edit:

For those those that care about such things, N3337 (~c++11), 22.4.2.2.2:

The location of any padding is determined according to Table 91.
                  Table 91 - Fill padding
State                               Location
adjustfield == ios_base::left       pad after
adjustfield == ios_base::right      pad before
adjustfield == internal and a
sign occurs in the representation   pad after the sign
adjustfield == internal and
representation after stage 1 began
with 0x or 0X                       pad after x or X
otherwise                           pad before

来源：https://stackoverflow.com/questions/17543883/correctly-pad-negative-integers-with-zeros-with-stdcout