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copied!<p>This is pretty simple, but very surprising if you're used to a higher-level language. <em>C does not manage memory for you</em>, and <em>C doesn't really have strings</em>. That <code>content</code> variable is a pointer, not a string. You have to manually allocate the space you need for the string before calling <code>strcat</code>. The correct way to write this code is something like this:</p> <pre><code>FILE *fp = fopen(filename, "r"); if (!fp) { syslog(LOG_INFO, "failed to open %s: %s", filename, strerror(errno)); return xstrdup("<!DOCTYPE html><html lang=\"en-US\"><head><title>Test</title>" "</head><body><h1>Does Work</h1></body></html>"); } else { size_t capacity = 4096, offset = 0, n; char *content = xmalloc(capacity); size_t n; while ((n = fread(content + offset, 1, capacity - offset, fp)) > 0) { offset += n; if (offset == capacity) { capacity *= 2; content = xrealloc(content, capacity); } } if (n < 0) syslog(LOG_INFO, "read error from %s: %s", filename, strerror(errno)); content[offset] = '\0'; fclose(fp); return content; } </code></pre> <p>Notes:</p> <ol> <li>Error messages triggered by I/O failures should ALWAYS include <code>strerror(errno)</code>.</li> <li><code>xmalloc</code>, <code>xrealloc</code>, and <code>xstrdup</code> are wrapper functions around their counterparts with no leading <code>x</code>; they crash the program rather than return <code>NULL</code>. This is almost always less grief than trying to recover from out-of-memory by hand in every single place where it can happen.</li> <li>I return <code>xstrdup("...")</code> rather than <code>"..."</code> in the failed-to-open case so that the caller can always call <code>free(content)</code>. Calling <code>free</code> on a string literal will crash your program.</li> <li>Gosh, that was a lot of work, wasn't it? This is why people tend to prefer to write web apps in a higher-level language. ;-)</li> </ol>

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