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POWhere do writes to stdout go when launched from a cygwin shell, no redirection
 

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  1. POWhere do writes to stdout go when launched from a cygwin shell, no redirection
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    <p>I have an application, let's call it myapp.exe, which is dual-mode console/GUI, built as /SUBSYSTEM:WINDOWS (There's a tiny 3KB shim myapp.com to cause cmd.exe to wait to display the new prompt.)</p> <p>If I launch from a command prompt:</p> <ul> <li><code>myapp</code> -> cmd.exe runs myapp.com which runs myapp.exe. stdout is initially a detached console, by using <code>AttachConsole</code> and <code>freopen("CONOUT$", "w", stdout)</code> my output appears in the command box. OK</li> <li><code>myapp.exe</code> -> cmd.exe displays the prompt too early (known problem), otherwise same as previous. Not a normal usage scenario.</li> <li><code>myapp &gt; log</code> -> stdout is a file, normal use of <code>std::cout</code> ends up in the file. OK</li> </ul> <p>If I launch from Windows explorer:</p> <ul> <li><code>myapp.com</code> -> console is created, stdout is console, output goes into console. Same result as using /SUBSYSTEM:CONSOLE for the entire program, except that I've added a pause when <code>myapp.com</code> is the only process in the console. Not a normal usage scenario.</li> <li><code>myapp.exe</code> -> stdout is a NULL handle, I detect this and hook <code>std::cout</code> to a GUI. OK</li> </ul> <p>If I launch from Matlab shell:</p> <ul> <li><code>system('myapp')</code> or <code>system('myapp.com')</code> or <code>system('myapp.exe')</code> -> For all three variations, stdout is piped to MatLab. OK</li> </ul> <p>If I launch from a cygwin bash shell:</p> <ul> <li><code>./myapp.com</code> -> Just like launch from cmd.exe, the output appears in the command box. OK</li> <li><code>./myapp</code> -> (bash finds <code>./myapp.exe</code>). <strong>This is the broken case</strong>. stdout is a non-NULL handle but output goes nowhere. This is the normal situation for running the program from bash and needs to be fixed!</li> <li><code>./myapp &gt; log</code> -> Just like launch from cmd.exe with file redirection. OK</li> <li><code>./myapp | cat</code> -> Similar to file redirection, except output ends up on the console window. OK</li> </ul> <p>Does anybody know what cygwin sets as stdout when launching a /SUBSYSTEM:WINDOWS process and how I can bind <code>std::cout</code> to it? Or at least tell me how to find out what kind of handle I'm getting back from <code>GetStdHandle(STD_OUTPUT_HANDLE)</code>?</p> <p>My program is written with Visual C++ 2010, without <code>/clr</code>, in case that matters in any way. OS is Windows 7 64-bit.</p> <p>EDIT: Additional information requested.</p> <p>CYGWIN environment variable is empty (or non-existent).</p> <p><code>GetFileType()</code> returns <code>FILE_TYPE_UNKNOWN</code>. <code>GetLastError()</code> returns <code>6 (ERROR_INVALID_HANDLE)</code>. It doesn't matter whether I check before or after calling <code>AttachConsole()</code>.</p> <p>However, if I simply ignore the invalid handle and <code>freopen("CONOUT$", "w", stdout)</code> then everything works great. I was just missing a way to distinguish between (busted) console output and file redirection, and <code>GetFileType()</code> provided that.</p> <p>EDIT: Final code:</p> <pre><code>bool is_console(HANDLE h) { if (!h) return false; ::AttachConsole(ATTACH_PARENT_PROCESS); if (FILE_TYPE_UNKNOWN == ::GetFileType(h) &amp;&amp; ERROR_INVALID_HANDLE == GetLastError()) { /* workaround cygwin brokenness */ h = ::CreateFile(_T("CONOUT$"), GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL); if (h) { ::CloseHandle(h); return true; } } CONSOLE_FONT_INFO cfi; return ::GetCurrentConsoleFont(h, FALSE, &amp;cfi) != 0; } bool init( void ) { HANDLE out = ::GetStdHandle(STD_OUTPUT_HANDLE); if (out) { /* stdout exists, might be console, file, or pipe */ if (is_console(out)) { #pragma warning(push) #pragma warning(disable: 4996) freopen("CONOUT$", "w", stdout); #pragma warning(pop) } //std::stringstream msg; //DWORD result = ::GetFileType(out); //DWORD lasterror = ::GetLastError(); //msg &lt;&lt; result &lt;&lt; std::ends; //::MessageBoxA(NULL, msg.str().c_str(), "GetFileType", MB_OK); //if (result == FILE_TYPE_UNKNOWN) { // msg.str(std::string()); // msg &lt;&lt; lasterror &lt;&lt; std::ends; // ::MessageBoxA(NULL, msg.str().c_str(), "GetLastError", MB_OK); //} return true; } else { /* no text-mode stdout, launch GUI (actual code removed) */ } } </code></pre>
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      1. POWhere do writes to stdout go when launched from a cygwin shell, no redirection
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    1. COIs that with the default Cygwin console (started via the "Cygwin Bash Shell" shortcut)? Have you got anything in the CYGWIN environment variable, in particular `tty`? `GetFileType()` can tell you what sort of handle you're dealing with.
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      1. POWhere do writes to stdout go when launched from a cygwin shell, no redirection
      1. USak2
    2. CO@ak2: `GetFileType` was just the ticket. If you make an answer I'll accept it.
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      1. POWhere do writes to stdout go when launched from a cygwin shell, no redirection
      1. USBen Voigt
 

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