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Editorial Team
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Asked: 2026-05-16T08:32:06+00:00

From a response to some question yesterday, I learned that it is nonportable and

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From a response to some question yesterday, I learned that it is nonportable and unsafe to write into one union member and read the value from another member of a different type, assuming underlying alignment of the members. So after some research I found a written source that repeats this claim and specifies a popular example – using union of int and float to find the binary representation of a float.

So, understanding that this assumption is not safe, I wonder – except for saving memory (duh…) what real use is there to unions?

Note: that is, under Standard C. Clearly, for a specific implementation, the rules are known in advance and can be taken advantage of.

EDIT: the word “unsafe”, due to association of recent years, is probably a bad choice of wording, but I think the intention in clear.

EDIT 2: Since this point repeats in the answers – saving memory is a valid argument. I wanted to know if there was something beyond that.

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1 Answer

  1. Editorial Team

    Yes.

    The provide a way of creating generic containers. Though, to get polymorphic behavior you must implement a vtable or type switching yourself…

    There are, however, one of those features that you only use when you need them and need rather rarely.

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