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copied!<p>Looking at your program, here is what happens:</p> <ol> <li>You fill the memory initially pointed to by <code>buffer0+buffPositionOutput</code> (Which is where, precisely? I don't know based on the code you give.) up to <code>buffer0+outputbuf.st_blksize</code> with data.</li> <li>You pass the address of the <code>buffer0</code> pointer to <code>posix_memalign</code>, which ignores its current value and overwrites it with a pointer to <code>outputbuf.st_blksize</code> bytes of newly-allocated memory.</li> <li>You write data from the newly-allocated block to disk; this might be anything, since you just allocated memory and haven't written anything there yet.</li> </ol> <p>This won't work, obviously. You probably want to initialize your buffer via <code>posix_memalign</code> at the top of your function, and then just overwrite the block's worth of data in it as you use your aligned buffer to repeatedly write data into the file. (Reset <code>buffpositionoutput</code> to zero after each time you write data, but don't re-allocate.) Make sure you <code>free</code> your buffer when you are done.</p> <p>Also, why are you using <code>pwrite</code> instead of <code>write</code>?</p> <p>Here's how I would implement <code>writeThis</code> (keeping your variable names so you can match it up with your version):</p> <pre><code>void writeThis(char *text) { char *buffer0; size_t buffPositionOutput = 0; posix_memalign(&buffer0, outputbuf.st_blksize, outputbuf.st_blksize); while (*text != 0) { ++text; ++buffPositionOutput; if (buffPositionOutput == outputbuf.st_blksize) { write(fdOutputFile, buffer0, outputbuf.st_blksize); buffPositionOuput = 0; } } if (buffPositionOutput != 0) { // what do you want to do with a partial block of data? Not sure. } } </code></pre> <p>(For speed, you might consider using <code>memcpy</code> calls instead of a loop. You would need to know the length of the data to write ahead of time though. Worry about that after you have a working solution that does not leak memory.)</p>

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