Geek asks and answers

Why is printf () an unclean function?

As far as I know, unclean functions are those that do not always return the same value when called with the same parameters (I have to skip something, or maybe I'm mistaken, correct me if I find it).

So why printf()is it considered an unclean function?

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6 answers

No, an "unclean" function is a function with side effects .

In other words, no matter how many times you call it, a pure function will affect nothing but its output.

For example, it is unclean , although it returns zero: foo

int x;
int foo() { x++; return 0; }
int bar() { return x; }

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Many answers explain that printfI / O has a side effect, but printfmay have other side effects. For example, the specifier %nallows you printfto write to the specified address (and is the cause of some security vulnerabilities).

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