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C: Why isn't size_t a C keyword?

Asked 2009-04-11T08:03:38.837
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sizeof is a C keyword. It returns the size in a type named size_t. However, size_t is not a keyword, but is defined primarily in stddef.h and probably other C standard header files too.

Consider a scenario where you want to create a C program which does not include any C standard headers or libraries. (Like for example, if you are creating an OS kernel.) Now, in such code, sizeof can be used (it is a C keyword, so it is a part of the language), but the type that it returns (size_t) is not available!

Does not this signify some kind of a problem in the C standard specification? Can you clarify this?

c types sizeof size-t
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sizeof is a keyword because, despite it's name and usage, it is an operator like + or = or < rather than a function like printf() or atoi() or fgets(). A lot of people forget (or just don't know) that sizeof is actually an operator, and is always resolved at compile-time rather than at runtime.

The C language doesn't need size_t to be a usable, consistent language. That's just part of the standard library. The C language needs all operators. If, instead of +, C used the keyword plus to add numbers, you would make it an operator.

Besides, I do semi-implicit recasting of size_ts to unsigned ints (and regular ints, but Kernighan and Ritchie will someday smite me for this) all the time. You can assign the return type of a sizeof to an int if you like, but in my work I'm usually just passing it straight on to a malloc() or something.

answered 2009-04-11T08:17:40.443

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