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POLibzip example contains uninitialised values when checked with Valgrind
 

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  1. POLibzip example contains uninitialised values when checked with Valgrind
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    <p>I've been using libzip to handle zip files, and have based my code on the example found in rodrigo's answer to <a href="https://stackoverflow.com/questions/10440113/simple-way-to-unzip-a-zip-file-using-zlib">this question</a>. Here's his code, for quick reference:</p> <pre class="lang-cpp prettyprint-override"><code>#include &lt;zip.h&gt; int main() { //Open the ZIP archive int err = 0; zip *z = zip_open("foo.zip", 0, &amp;err); //Search for the file of given name const char *name = "file.txt"; struct zip_stat st; zip_stat_init(&amp;st); zip_stat(z, name, 0, &amp;st); //Alloc memory for its uncompressed contents char *contents = new char[st.size]; //Read the compressed file zip_file *f = zip_fopen(z, "file.txt", 0); zip_fread(f, contents, st.size); zip_fclose(f); //And close the archive zip_close(z); } </code></pre> <p>I traced the errors I subsequently got from Valgrind back to this code- it complains of an uninitialised value when opening the zipped "file.txt" using 'zip_fopen()`. </p> <pre><code>==29256== Conditional jump or move depends on uninitialised value(s) ==29256== at 0x5B4B290: inflateReset2 (in /usr/lib/libz.so.1.2.3.4) ==29256== by 0x5B4B37F: inflateInit2_ (in /usr/lib/libz.so.1.2.3.4) ==29256== by 0x4E2EB8C: zip_fopen_index (in /usr/lib/libzip.so.1.0.0) ==29256== by 0x400C32: main (main.cpp:24) ==29256== Uninitialised value was created by a heap allocation ==29256== at 0x4C244E8: malloc (vg_replace_malloc.c:236) ==29256== by 0x5B4B35B: inflateInit2_ (in /usr/lib/libz.so.1.2.3.4) ==29256== by 0x4E2EB8C: zip_fopen_index (in /usr/lib/libzip.so.1.0.0) ==29256== by 0x400C32: main (main.cpp:24) ==29256== ==29256== ==29256== HEAP SUMMARY: ==29256== in use at exit: 71 bytes in 1 blocks ==29256== total heap usage: 26 allocs, 25 frees, 85,851 bytes allocated ==29256== ==29256== 71 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==29256== at 0x4C24A72: operator new[](unsigned long) (vg_replace_malloc.c:305) ==29256== by 0x400BEE: main (main.cpp:19) </code></pre> <p>I can't see where the uninitialised value is coming from in this code. Can anyone trace this, or does the fault lie with libzip itself? Should I switch to another zip library- for example, Minizip?</p> <p>EDIT: The 71 bytes are the contents of file.txt which was read in- <code>delete[] contents;</code> tagged on the end will eliminate that.</p> <p>(I'd have left a comment on the original answer to draw attention to the issue, but I do not have the requisite rep.)</p>
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    1. USSam Finnigan
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      1. POLibzip example contains uninitialised values when checked with Valgrind
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    1. COThe stack trace is slightly odd, you call zip_fopen but it says you're in zip_fopen_index. Can't see that there's any `#define` that defines either in terms of the other, so have to ask if it's the right stack trace.
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      1. USJoachim Isaksson
    2. COI agree! I couldn't see anything like that in zip.h, it was another reason to ask here. Definitely the right trace though, I just ran it again to check. I'd be interested to see if anyone else can reproduce this.
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      1. USSam Finnigan
    3. COYou'd have to look through the source code for `inflateReset2()` to try to determine what variable is being used as a conditional before it was initialized. The source code holds the answer to the `zip_fopen_index()` question, too, I'm sure.
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