My understanding is that you can get gcc-4.6 from macports.  4.2 is no longer supported in the main branch.

Rather than overwrite, configure the build with --prefix=/opt/gdc so installation is separate from your system compiler.   Then be sure to your PATH to include the bin location.

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Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';