Are flexible array members valid in C++?

c++ flexible-array-member
MSN picture MSN · Dec 10, 2010 · Viewed 29.5k times · Source

In C99, you can declare a flexible array member of a struct as such:

struct blah
{
    int foo[];
};

However, when someone here at work tried to compile some code using clang in C++, that syntax did not work. (It had been working with MSVC.) We had to convert it to:

struct blah
{
    int foo[0];
};

Looking through the C++ standard, I found no reference to flexible member arrays at all; I always thought [0] was an invalid declaration, but apparently for a flexible member array it is valid. Are flexible member arrays actually valid in C++? If so, is the correct declaration [] or [0]?

Answer

Martin v. Löwis picture Martin v. Löwis · Dec 10, 2010

C++ was first standardized in 1998, so it predates the addition of flexible array members to C (which was new in C99). There was a corrigendum to C++ in 2003, but that didn't add any relevant new features. The next revision of C++ (C++2b) is still under development, and it seems flexible array members still aren't added to it.

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