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POWhy sending datagram doesn't work if I don't create a TCP connection first?
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  1. POWhy sending datagram doesn't work if I don't create a TCP connection first?
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    copied!<p>The following c++ program should convert each line to uppercase using socket datagram to communicate between two threads.</p> <pre><code>Example: Hello World!&lt;return&gt; HELLO WORLD! 123abc!&lt;return&gt; 123ABC! &lt;return&gt; &lt;end program&gt; </code></pre> <p>The program as written works for me, however if I comment the <code>bugfix()</code> function call in the main the program wait indefinitely after the first line of input.</p> <pre><code>Example: Hello World!&lt;return&gt; &lt;the program wait indefinitely&gt; </code></pre> <p>This happen on windows 7 with the last update as 10/04/2011 using the last MinGW32.</p> <pre><code>#include &lt;iostream&gt; #include &lt;cstdlib&gt; #include &lt;cctype&gt; #include &lt;sys/types.h&gt; #include &lt;winsock.h&gt; #include &lt;windows.h&gt; #include &lt;process.h&gt; using namespace std; #define CHECK(exp, cond) do { typeof(exp) _check_value_ = exp; check(_check_value_ cond, _check_value_, __LINE__, #exp #cond); } while(0) template &lt;class T&gt; void check(bool ok, T value, int line, const char* text) { if (!ok) { cerr &lt;&lt; "ERROR(" &lt;&lt; line &lt;&lt; "):" &lt;&lt; text &lt;&lt; "\nReturned: " &lt;&lt; value &lt;&lt; endl; cerr &lt;&lt; "errno=" &lt;&lt; errno &lt;&lt; endl; cerr &lt;&lt; "WSAGetLastError()=" &lt;&lt; WSAGetLastError() &lt;&lt; endl; exit(EXIT_FAILURE); } } #define DATA_CAPACITY 1000 #define PORT 23584 #define TEST_IP "192.0.32.10" #define MYSELF "127.0.0.1" #define DST_IP MYSELF sockaddr_in address(u_long ip, u_short port) { sockaddr_in addr = { }; addr.sin_family = AF_INET; addr.sin_port = port; addr.sin_addr.s_addr = ip; return addr; } void __cdecl client_thread(void* args) { SOCKET s = *(SOCKET*)args; sockaddr_in addr = address(inet_addr(DST_IP), htons(PORT)); char data[DATA_CAPACITY]; while (1) { cin.getline(data, DATA_CAPACITY); int data_len = strlen(data); CHECK(sendto(s, data, data_len, 0, (sockaddr*)&amp;addr, sizeof addr), &gt;= 0); CHECK(recvfrom(s, data, DATA_CAPACITY, 0, NULL, NULL), &gt;= 0); cout &lt;&lt; data &lt;&lt; endl; if (data_len == 0) break; } CHECK(closesocket(s), == 0); } void __cdecl server_thread(void* args) { SOCKET s = *(SOCKET*)args; sockaddr_in addr = address(INADDR_ANY, htons(PORT)); int addr_size = sizeof addr; CHECK(bind(s, (sockaddr*)&amp;addr, sizeof addr), != SOCKET_ERROR); char data[DATA_CAPACITY]; while (1) { int data_len = recvfrom(s, data, DATA_CAPACITY, 0, (sockaddr*)&amp;addr, &amp;addr_size); CHECK(data_len, &gt;= 0); for (int i = 0; i &lt; data_len; i++) if (islower(data[i])) data[i] = toupper(data[i]); CHECK(sendto(s, data, data_len, 0, (sockaddr*)&amp;addr, addr_size), &gt;= 0); if (data_len == 0) break; } CHECK(closesocket(s), == 0); } // This function create a TCP connection with www.example.com and the close it void bugfix() { SOCKET s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP); sockaddr_in addr = address(inet_addr(TEST_IP), htons(80)); connect(s, (sockaddr*)&amp;addr, sizeof addr); CHECK(closesocket(s), == 0); } int main() { cout &lt;&lt; "Convert text to uppercase, an empty line terminate the program" &lt;&lt; endl; WSADATA wsaData; CHECK(WSAStartup(MAKEWORD(2, 2), &amp;wsaData), == 0); SOCKET client = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP); SOCKET server = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP); CHECK(client, != INVALID_SOCKET); CHECK(server, != INVALID_SOCKET); // if this function is not called the program doesn't work bugfix(); HANDLE hClient = (HANDLE)_beginthread(client_thread, 0, &amp;client); HANDLE hServer = (HANDLE)_beginthread(server_thread, 0, &amp;server); HANDLE h[] = { hClient, hServer }; WaitForMultipleObjects(sizeof h / sizeof *h, h, TRUE, INFINITE); CHECK(WSACleanup(), == 0); return EXIT_SUCCESS; } </code></pre>
 

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