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POIs there a cross-platform way to reliably find the stdout file descriptor with ctypes?
 

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  1. POIs there a cross-platform way to reliably find the stdout file descriptor with ctypes?
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    <p>I have some code that uses ctypes to try to determine if the file pointed to by <code>sys.stdout</code> is <em>actually</em> <code>stdout</code>. I know that on any POSIX-compliant system, and even on Windows, it should be safe to assume this is true if <code>sys.stdout.fileno() == 1</code>, so my question is not how to do this in general.</p> <p>In my code (which is already using ctypes for something unrelated to my question) I carelessly had something like:</p> <pre><code>libc = ctypes.CDLL(ctypes.util.find_library('c')) real_stdout = libc.fileno(ctypes.c_void_p.in_dll(libc, 'stdout')) if sys.stdout.fileno() == real_stdout: ... </code></pre> <p>This works perfectly fine on Linux, so I didn't really think about it much. It looked nicer and more readable than hard-coding <code>1</code> as the file descriptor. But I found a few days later that my code wasn't working on OSX.</p> <p>It turns outs OSX's libc doesn't export any symbol called 'stdout'. Instead its stdio.h has stdout defined as:</p> <pre><code>#define stdout __stdoutp </code></pre> <p>If I change my code to <code>c_void_p.in_dll(libc, '__stdoutp')</code> my code works as expected, but of course that's OSX-only. Windows, it turns out, has a similar issue (at least if using MSVC).</p> <p>I will probably just change my code to use <code>1</code>, but my question still stands, out of curiosity, if there's a cross-platform way to get the <code>stdio</code> pointer (and likewise <code>stdin</code> and <code>stderr</code>) without <em>assuming</em> that it's using the POSIX-compliant descriptor?</p>
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    1. USIguananaut
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      1. POIs there a cross-platform way to reliably find the stdout file descriptor with ctypes?
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    1. COA "file descriptor" isn't a cross-platform concept. It's a Posix-specific. You can use `fileno(stdout)` on any Posix platform, though there's a also a predefined macro for that value named `STDOUT_FILENO`.
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      1. POIs there a cross-platform way to reliably find the stdout file descriptor with ctypes?
      1. USKerrek SB
    2. COnote that if `sys.stdout` has been replaced the original `stdout` remains in `sys.__stdout__` (unless your code changes that too). See that `sys.__stdout__.fileno()` => `1`
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      1. POIs there a cross-platform way to reliably find the stdout file descriptor with ctypes?
      1. USDan D.
    3. COnote that file decriptors (an integer "handle") is a very different thing than the stdout FILE* in C. There's no cross platform ABI for the symbols found in C libraries, so taking that path is futile. Hard coding 1 as the file descriptor for stdout would be almost infinitely more portable.
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