What is the c(current_date) ?

[Tony Li]

This question may sounds naive but what is the c(current_date)? is it a scalar of string or a local?

disp c(current_date) indicates that c(current_date) is just a string scalar but disp "`c(current_date)'" shows that it is a local macro

what is the truth here?

[Maarten Buis]

Using `' around a returned value forces Stata to evaluate it first. This can be convenient when the returned value contains a number and you want to feed the returned value to an option of a subsequent command that requires a number. If you enter it without `' that command will complain.

[Tony Li]

Thanks, Buis! So the `' does not necessarily means that c(current_date) is a local? I also find that we can use disp `r(N)' after summarize command. Can we treat the c(current_date) as a scalar?

[daniel klein]

As far as I understand it (hope I am correct) you can use r(), c(), e() and s() scalars and macros without single quotes, wherever Stata allows an expression. Thus,

display c(current_date)

will work, as will

generate foo = c(alpha)

although the latter is a nonsensical example. Because display and generate evaluate expressions, there is no need to use single quotes to force evaluation. Given this, it should not be surprising that

forvalues j = 1/r(N) {

}

results in an invalid syntax error, as Stata does not expect, and in fact not allow, an expression in the forvalues command. Typing

forvalues j = 1/`r(N)' {

}

will work fine, as will

forvalues j = 1/`= r(N)' {

}

as both force evaluation before forvalues interprets the numlist it expects to see. Note that I did not enclose r(N) in quotes in the second example.

I hope this helps.

Best
Daniel