This worked for me, I had to change the function signature but it's actually better in my case as it statically checks the array length:
void foo(std::array<uint8_t, 3> a) { /* use a.data() instead of a */ }
foo({0x01, 0x02, 0x03}); // OK
foo({0x01, 0x02}); // Works, at least on GCC 4.9.1. The third value is set to zero.
foo({0x01, 0x02, 0x03, 0x04}); // Compilation error.
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