It has been a while since I posted any questions on StackOverflow; I hope I remember more or less the appropriate way to address a question (sorry in advance).
I was playing with C++ streams and the FMT library, which provides a preview to C++23 print. Streams are chill when setting fillers to complete the display width of an integer. Example:
const int y = 730;
cout << "y = " << setw(5) << y << endl;
cout << "y = " << setfill('0') << setw(5) << y << endl;
cout << "y = " << setfill('X') << setw(5) << y << endl;
cout << "y = " << setfill('*') << setw(5) << y << endl;
The output is
y = 730
y = 00730
y = XX730
y = **730
I was trying to set the same fillers (including ‘X’ and ‘*’ chars) using fmt::print—something like:
print("y = {:5d}\n", y);
print("y = {:05d}\n", y);
Well, I failed to include ‘X’ and ‘*’. I am not claiming it is a good idea to have random chars as fillers; I am just curious as I need to explain the difference between these commands to students.
Thanks in advance.
Vivian
>Solution :
The manual shows following grammar for integer format specifiers:
format_spec ::= [[fill]align][sign]["#"]["0"][width]["." precision]["L"][type]
fill ::= <a character other than '{' or '}'>
align ::= "<" | ">" | "^"
Here format_spec is the part inside of {: }.
So specifying a custom filler (fill) also requires specifying alignment (you want >, i.e. align to the right):
fmt::print("y = {:X>5d}\n", y); // XX730
fmt::print("y = {:*>5d}\n", y); // **730