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    <p>Rereading your code, I have some more observations:</p> <ol> <li><p>It is apparent you are not passing the correct parameters to <code>fwrite</code>. The first parameter is a pointer to a buffer of memory, not another <code>FILE*</code>. In this case you're copying bizarre memory into the new executable, which is why it cannot be executed.</p> <p>If you have a block of memory you would like to copy to an executable, simply <code>fwrite</code> that block of memory:</p> <pre><code>FILE* fp_out = fopen("testing.exe", "wb"); /* ... */ fwrite(value, sizeof(value), 1, fp_out); </code></pre> <p>However, this assumes <code>value</code> is a full and complete executable image suitable for execution (you probably need a <code>chmod +x testing.exe</code>). I'm left to wonder, given an extension of <code>.exe</code>, if this binary image even contains a valid executable for your platform.</p></li> <li><p>You do not want to use <code>strlen</code> when dealing with a supposed executable image, even if it is "stored" in a <code>char*</code>. Executables contain byte values of 0, which are the C-string delimiter character NUL (e.g. <code>'\0'</code>). This will cause <code>strlen</code> to fumble. You'll need to use <code>sizeof</code> or keep track of the size of the executable image.</p></li> <li><p>It would be best to use <code>"wb"</code> in your call to <code>fopen</code> if you made the effort to use <code>"rb"</code> in your call to <code>fmemopen</code>. This way you do not receive newline translation on systems which do this (<a href="http://msdn.microsoft.com/en-us/library/yeby3zcb.aspx" rel="nofollow">Windows</a>). If you're on a platform which does not make this requirement, either remove the <code>b</code> from the calls or keep it. Whatever you choose, be consistent.</p></li> </ol>
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    1. COI think this is the real problem - the OP is writing data from the `FILE` struct that `fmemopen()` returns, not the array (`value`) which that `FILE` object references as its buffer...
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    2. COAgreed, and the `strlen` will certainly not be correct if the executable image contains even a single zero-valued byte.
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    3. COThanks a lot for your advices. I agree about the strlen,"wb" (fixed both), but for the FILE * stream I am mainly doing it to be able to read and use it as a file that could be read by other part of the program without having a real file written on the hard drive (if I will keep reading and writing through the value then fmemopen is useless).
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