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POHow do I read the results of a system() call in C++?
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  1. POHow do I read the results of a system() call in C++?
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    copied!<p>I'm using the following code to try to read the results of a <code>df</code> command in Linux using <code>popen</code>.</p> <pre><code>#include &lt;iostream&gt; // file and std I/O functions int main(int argc, char** argv) { FILE* fp; char * buffer; long bufSize; size_t ret_code; fp = popen("df", "r"); if(fp == NULL) { // head off errors reading the results std::cerr &lt;&lt; "Could not execute command: df" &lt;&lt; std::endl; exit(1); } // get the size of the results fseek(fp, 0, SEEK_END); bufSize = ftell(fp); rewind(fp); // allocate the memory to contain the results buffer = (char*)malloc( sizeof(char) * bufSize ); if(buffer == NULL) { std::cerr &lt;&lt; "Memory error." &lt;&lt; std::endl; exit(2); } // read the results into the buffer ret_code = fread(buffer, 1, sizeof(buffer), fp); if(ret_code != bufSize) { std::cerr &lt;&lt; "Error reading output." &lt;&lt; std::endl; exit(3); } // print the results std::cout &lt;&lt; buffer &lt;&lt; std::endl; // clean up pclose(fp); free(buffer); return (EXIT_SUCCESS); } </code></pre> <p>This code is giving me a "Memory error" with an exit status of '2', so I can see <em>where</em> it's failing, I just don't understand <em>why</em>.</p> <p>I put this together from example code that I found on <a href="http://ubuntuforums.org/showthread.php?t=285287" rel="nofollow noreferrer">Ubuntu Forums</a> and <a href="http://en.cppreference.com/w/cpp/io/c/fread" rel="nofollow noreferrer">C++ Reference</a>, so I'm not married to it. If anyone can suggest a better way to read the results of a system() call, I'm open to new ideas.</p> <p><strong>EDIT to the original:</strong> Okay, <code>bufSize</code> is coming up negative, and now I understand why. You can't randomly access a pipe, as I naively tried to do.</p> <p>I can't be the first person to try to do this. Can someone give (or point me to) an example of how to read the results of a system() call into a variable in C++?</p>
 

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