[cfe-dev] Flexible array members in a union

Tal Shnaiderman via cfe-dev cfe-dev at lists.llvm.org
Tue Sep 7 13:56:28 PDT 2021


I hope this is the right forum for the question below.

In the DPDK project we're using clang as the compiler on Windows.

I noticed that there is a size difference between a Windows and a Linux if flexible array members are defined in a union inside a struct.


struct umr {
	uint32_t temp;
	union {
		uint32_t res_dp[0];
		uint32_t res_dp2[0];

On linux with GCC the result of 

sizeof(struct umr) = 4

When on Windows with clang 11.0.0 I'm getting 

sizeof(struct umr) = 8

Is this a bug? or flexible array members in a union behavior is undefined?


Tal Shnaiderman.

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