title: Does btowc(c) always return ( c in 0..127 ? c : WEOF )?
body: <p>Is <code>btowc(3)</code> locale-dependant? I thought that with <code>LANG=en_US.iso88591</code> it would return some european chars for bytes between 128 and 255, but it returns WEOF.</p>
  
  <pre><code>$ printf '\xFF\n' | iconv -f iso88591
  ÿ
  $ LANG=en_US.iso88591 ./a.out
  255 -1
  </code></pre>
  
  <p>_</p>
  
  <pre><code>int main() {
    int i = 0xFF;
    printf("%d %d\n", i,  btowc(i));
  }
  </code></pre>