Why does printf return an int instead of a size_t in C

Question

Shouldn't the return be of type size_t instead? Because the size of objects in C is of this type, including the string passed to printf.

Answer 1

Why printf returns an int in C?
Shouldn't be of type size_t instead?

It could have been, but certainly an early design decision was to accommodate a return value of the negative EOF to indicate error.

size_t was something of an afterthought in early design choices. Many functions used int where size_t is used now in those pre-standard days.

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fprintf() has an environmental limit "The number of characters that can be produced by any single conversion shall be at least 4095.", so any print that is attempting long output may run into that limit before INT_MAX/SIZE_MAX concerns.

Answer 2

You're largely right - actually printf should return a larger type, since it's theoretically possible to output many more bytes than the size of the largest object that can fit in memory, e.g. printf("%s%s", largest_string, largest_string) or even more trivial examples using field widths/precisions.

The reason is just a historical mistake that we're stuck with. It's particularly bad with snprintf, which is artificially limited to INT_MAX and is forced to return an error if you attempt to create a longer string with it.