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    <p>Using posix functionality (so, will work on linux and any system that complies with posix standard), you can use a combination of pipe/execl/dup. In short what happens is:</p> <ul> <li>create 2 pipes (one to read and one to write to the child)</li> <li>fork the current process. This keeps open the same fd</li> <li>close the current stdin/stdout. Then use dup (which uses the lowest available descriptor to duplicate what you give to it)</li> <li>execl the child process</li> </ul> <p>Pay attention some flushes are needed. The code of the parent is:</p> <pre><code>#include &lt;sys/types.h&gt; #include &lt;unistd.h&gt; #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; int main () { pid_t pid; int pipe_in[2]; /* This is the pipe with wich we write to the child process. */ int pipe_out[2]; /* This is the pipe with wich we read from the child process. */ if (pipe (pipe_in) || pipe (pipe_out)) { fprintf (stderr, "Error in creating pipes!\n"); exit (1); } /* Attempt to fork and check for errors */ if ((pid = fork ()) == -1) { fprintf (stderr, "Error in fork!\n"); exit (1); } if (pid) { /* The parent has the non-zero PID. */ char temp[100]; int result; FILE* child_in; FILE* child_out; child_in = fdopen(pipe_out[0],"r"); child_out = fdopen(pipe_in[1],"w"); close(pipe_out[1]); close(pipe_in[0]); fprintf(child_out, "something\n"); fgets(temp,100,child_in); printf(" Read from child %s \n", temp); /* Send a command to the child. */ fprintf(child_out, "quit\n"); fflush(child_out); fgets(temp,100,child_in); printf(" Read from child %s \n", temp); wait (&amp;result); /* Wait for child to finish */ } else { /* The child has the zero pid returned by fork*/ close (1); dup (pipe_out[1]); /* dup uses the lowest numbered unused file descriptor as new descriptor. In our case this now is 1. */ close (0); /* dup uses the lowest numbered unused file descriptor as new descriptor. In our case this now is 0. */ dup (pipe_in[0]); close (pipe_out[0]); close (pipe_out[1]); close (pipe_in[0]); close (pipe_in[1]); execl ("child", "child", NULL); exit(1); /* Only reached if execl() failed */ } return 0; } </code></pre> <p>A simple child is:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; int main () { char temp[100]; do { printf ("In child: \n"); fflush (stdout); fgets (temp, 100, stdin); printf ("Child read %s\n", temp); fflush (stdout); } while (!strstr (temp, "quit")); return 0; } </code></pre> <p>You can compile them with:</p> <pre><code>gcc -o parent parent.c gcc -o child child.c ./parent </code></pre> <p>And you will see</p> <p>Read from child In child: Read from child Child read quit</p>
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    1. POWhat is the best way to create an rw pipe with c++?
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    1. USvladmihaisima
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    1. POWhat is the best way to create an rw pipe with c++?
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    1. COBetter to use `dup2` which allows you to specify the new file descriptor to be used.
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    2. COThanks, I could make this work.
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