如何在C中将size_t转换为int？

Question

Is it possible to safely convert a variable with type size_t to type int in C99?

I appreciate that size_t in unsigned, but in the case where we need an int representation, what can we do?

Answer 1

Is it possible to safely convert a variable with type size_t to type int in C99?

It depends on what you mean by "safely".

The maximum representable value of type size_t is typically larger than the maximum representable value of type int . If you are asking whether all size_t values can be converted to type int without losing information then the answer is probably "no" for your implementation, and definitely "no" in a portability sense.

If you are asking whether it is possible to detect that a size_t value is too large for type int without actually trying to perform an explicit conversion, so as to avoid the implementation-defined result and possible signal in the event that the value is out of range and fall back to some kind of graceful failure, then the answer is "yes". You can safely compare the value in question with INT_MAX . Suitable value-preserving conversions will be applied automatically to bring the operands of the <= or > operator to a common type, and the operation will yield the appropriate result.

I appreciate that size_t in unsigned, but in the case where we need an int representation, what can we do?

If you're just asking about syntax, assuming that the values you want to convert will always be representable as type int , then you can cast ( int x; x = (int) my_size_t_value; ), but you don't actually need to do anything at all in some contexts. In particular, you can directly assign a size_t to an int variable, or directly pass it to an int parameter of a non-variadic function with an in-scope prototype, and in those cases the appropriate conversion will be performed automatically.