CODEWITHSUNDEEP
tclstdout
user1610810
user1610810

Reputation: 99

Is stdout necessary in tcl?

I'm very new to tcl and I hope to become proficient in this language, so I thought I should ask if there was a reason why some example codes have stdout in the code and some just use puts. The book doesn't seem to explain this. Was the IDE updated to automatically assume stdout?

Upvotes: 1

Views: 547

Answers (1)

Donal Fellows
Donal Fellows

Reputation: 137767

The puts command writes to stdout if you don't provide it with a channel name (and has worked this way since… well, since forever). If you want, you can put it in or leave it out; it doesn't matter, but might make things clearer if done one way or the other. Let it be your choice. The only mandatory argument to puts is the string to write.

In performance terms, it's slightly faster to omit the value, but you should disregard that as the additional cost of a lookup is absolutely measly by comparison with the cost of doing IO at all. Clarity of expression is the only valid reason for picking one over the other.

There is a case where it matters though. If you want to write code that writes to standard output by default, but where you can override it to write to a file (or a socket or a pipe or …) then it's much easier to have the channel name stored in a variable (that is set to stdout by default, of course). Like that, all your code is the same except for one bit: it's not a good idea to close stdout normally. That's easy to avoid with code like this:

# Also don't want to close stdin or stderr...
if {![string match std* $channel]} {
    close $channel
}

Upvotes: 3

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