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POHowto use readlink with dynamic memory allocation
 

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    <h2>Problem:</h2> <p>On a linux machine I want to read the target string of a link. From documentation I have found the following code sample (without error processing):</p> <pre><code>struct stat sb; ssize_t r; char * linkname; lstat("&lt;some link&gt;", &amp;sb); linkname = malloc(sb.st_size + 1); r = readlink("/proc/self/exe", linkname, sb.st_size + 1); </code></pre> <p>The probelm is that sb.st_size returns 0 for links on my system.</p> <p>So how does one allocate memory dynamically for readline on such systems?</p> <p>Many thanks!</p> <hr> <h2>One possible solution:</h2> <p>For future reference. Using the points made by jilles:</p> <pre><code>struct stat sb; ssize_t r = INT_MAX; int linkSize = 0; const int growthRate = 255; char * linkTarget = NULL; // get length of the pathname the link points to if (lstat("/proc/self/exe", &amp;sb) == -1) { // could not lstat: insufficient permissions on directory? perror("lstat"); return; } // read the link target into a string linkSize = sb.st_size + 1 - growthRate; while (r &gt;= linkSize) { // i.e. symlink increased in size since lstat() or non-POSIX compliant filesystem // allocate sufficient memory to hold the link linkSize += growthRate; free(linkTarget); linkTarget = malloc(linkSize); if (linkTarget == NULL) { // insufficient memory fprintf(stderr, "setProcessName(): insufficient memory\n"); return; } // read the link target into variable linkTarget r = readlink("/proc/self/exe", linkTarget, linkSize); if (r &lt; 0) { // readlink failed: link was deleted? perror("lstat"); return; } } linkTarget[r] = '\0'; // readlink does not null-terminate the string </code></pre>
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