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A special instance of this guidance involves non-C++ code compiled by a different compiler, such as C standard library implementations that are exposed via the C++ standard library. C standard library functions are exposed with C++ signatures, and the type system frequently assists in ensuring that types match appropriately. This process disallows passing a pointer to a C++ object to a function expecting a char * without additional work to suppress the type mismatch. However, some C standard library functions accept a void * for which any C++ pointer type will suffice. Passing a pointer to a nonstandard-layout type in this situation results in indeterminate behavior because it depends on the behavior of the other language as well as on the layout of the given object. For more information, see rule EXP64-CPP. Do not call a function with a mismatched language linkage.
Only pass a nonstandard-layout type object across execution boundaries when both sides of the execution boundary adhere to the same ABI. This is permissible if the same version of a compiler is used to compile both sides of the execution boundary, or if the compiler used to compile both sides of the execution boundary is ABI-compatible across multiple versions, or if the differing compilers document that they adhere to the same ABI.
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