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POWhy ReadFile() doesn't return 0 ? Program tries to read data from pipe forever
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  1. POWhy ReadFile() doesn't return 0 ? Program tries to read data from pipe forever
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    copied!<p>code:</p> <p>This is from much larger MS example ( <a href="http://msdn.microsoft.com/en-us/library/ms682499(VS.85).aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/ms682499(VS.85).aspx</a> ). And of course I tried the whole example before, that my snipped below is where I stripped it down to the problem. The thing is how I'm supposed to break out of this loop if all I get is <code>1</code>. How to do signal that there is no more data to read ?</p> <p>(Compiler is MiGW.)</p> <p>It looks like the MS example is broken, this is one of the comments there: <em>Parent process needs to close handles that it passes to child process after the CreateProcess() call. Not doing so will cause the parent to wait forever on ReadFile().</em></p> <pre><code>#include &lt;iostream&gt; #include &lt;windows.h&gt; using namespace std; int main() { cout &lt;&lt; "\n-&gt;Start of parent execution.\n"; SECURITY_ATTRIBUTES saAttr; saAttr.bInheritHandle = TRUE; saAttr.lpSecurityDescriptor = NULL; HANDLE g_hChildStd_OUT_Rd = NULL; HANDLE g_hChildStd_OUT_Wr = NULL; CreatePipe(&amp;g_hChildStd_OUT_Rd, &amp;g_hChildStd_OUT_Wr, &amp;saAttr, 0); STARTUPINFO siStartInfo; PROCESS_INFORMATION piProcInfo; ZeroMemory( &amp;siStartInfo, sizeof(STARTUPINFO) ); siStartInfo.hStdOutput = g_hChildStd_OUT_Wr; siStartInfo.dwFlags |= STARTF_USESTDHANDLES; CreateProcess(NULL, (char*)"cmd /c dir", // command line NULL, // process security attributes NULL, // primary thread security attributes TRUE, // handles are inherited 0, // creation flags NULL, // use parent's environment NULL, // use parent's current directory &amp;siStartInfo, // STARTUPINFO pointer &amp;piProcInfo); // receives PROCESS_INFORMATION CHAR chBuf[4096]; DWORD dwRead; // ~~~~~~this loop here~~~~~- how to break out of it ? while(true) { cout &lt;&lt; "ReadFile: " &lt;&lt; ReadFile( g_hChildStd_OUT_Rd, chBuf, 4096, &amp;dwRead, NULL) &lt;&lt; endl; } cout &lt;&lt; "\n-&gt;End of parent execution.\n"; } </code></pre>
 

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