Question

typedef union { unsigned x; } T;

T a;
a.x = 3;

int main() { return 0; }

Trying to compile this code, with gcc t.c, I get

error: expected '=', ',', ';', 'asm' or '__attribute__' before '.' token

using

gcc --version
gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3

When I move a.x = 3; inside main, it behaves as expected.

I wish to find the passage from

ISO/IEC 9899:TC3

where it is explained that it is forbidden to assign values to a union in global namespace.

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EDIT: with structures it happens the same.

Answer 1

I wish to find the passage from ISO/IEC 9899:TC3 where it is explained that it is forbidden to assign values to a union in global namespace.

It is described in the 6.9p1 of C99 (syntax of a translation-unit). You cannot have a statement outside of a function.