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POFunction not free-ing in time
 

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  1. POFunction not free-ing in time
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    <p>I've had a look at a few other questions on SO but none of them seem to address a similar problem. </p> <p>I have a function which sorts an array (using heap sort) and calculates the median. The heap sort routine has been taken directly from Numerical Recipies. </p> <p>I am <code>calloc</code>ing and <code>free</code>ing an array inside the median function, but <code>free</code> doesn't seem to be freeing up the space in time. Here's some code to illustrate what I mean :</p> <pre><code>int calcMedian(int n1, int n2, int *dat) { int ii, npt; int *inparr, retval; npt = n2 - n1 + 1; /* Number of elements in array */ inparr = calloc(npt+1, sizeof(*inparr)); for(ii = n1; ii &lt;= n2; ii++) inparr[ii-n1+1] = dat[ii]; /* ii-n1+1 because heapsort function likes arrays to start from 1 */ heapsortInt(npt, inparr); /* The error isn't here, function has been previously debugged. Sorting is in-place.*/ if (npt % 2) retval = inparr[(npt+1)/2]; else retval = (inparr[npt/2]+inparr[npt/2+1])/2; free(inparr); return(retval); } </code></pre> <p>The function <code>heapsortInt</code> has been quite thoroughly debugged and has been used in several other places without issue. Now I call my function <code>calcMedian</code> in a loop like so :</p> <pre><code>for(ii = 0; ii &lt; maxval; ii++) { index = ii * maxpt; med1 = calcMedian(index, index+npt1[ii]-1, data1+index); med2 = calcMedian(index, index+npt2[ii]-1, data2+index); } </code></pre> <p>where the relevant variables are defined below :</p> <pre><code>int *data1, *data2; int *npt1, *npt2; data1 = calloc(maxval * maxpt, sizeof(*data1)); data2 = calloc(maxval * maxpt, sizeof(*data2)); npt1 = calloc(maxval, sizeof(*npt1)); npt2 = calloc(maxval, sizeof(*npt2)); </code></pre> <p>So I'm basically passing different sections of one large array into <code>calcMedian</code> and getting back the necessary median values. </p> <p><strong>THE PROBLEM:</strong> <code>calcMedian</code> seems to be crashing when it hits the second function call. I ran it through valgrind, and this is what it told me:</p> <pre><code>Invalid read of size 4 at 0x43F67E: calcMedian /* Line no. pointing to calloc in calcMedian */ by 0x4416C9: main /* Line no pointing to second call of calcMedian */ Address 0x128ffdc0 is 6,128 bytes inside a block of size 110,788 free'd at 0x4A063F0: free by 0x43F728: calcMedian /* Line no. pointing to free in calcMedian */ by 0x4416C9: main /* Line no pointing to first call of calcMedian */ </code></pre> <p>Is this a problem with <code>free</code>? Am I <code>free</code>ing and <code>calloc</code>ing too frequently? I don't know where to start debugging this. Any help will be wonderful! </p> <p><strong>DISCLAIMER:</strong> The computer with the actual code cannot access the internet. I've reproduced here as accurately as I can the code that causes the problem. If there are any missing semicolons etc. that's my fault, it definitely isn't there in the original code.</p> <p>Edit: Fixed some transcription errors. I'll try and get the original code up ASAP, but from me looking through both of them now this seems to be fine.</p>
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    1. CO`free` always frees "in time". Without a true [SSCCE](http://sscce.org), it's hard to give any specific advice here...
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      1. POFunction not free-ing in time
      1. USOliver Charlesworth
    2. COYour problem is mots likely an index out of bounds. `index+npt1[ii]-1` or another is probably calculating an out of bound memory address that by chance points to valid, but recently freed memory. On a side note: use stack arrays instead of `calloc` unless your array has to persist beyond the scope that allocated it or those arrays are multiple megabytes large.
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      1. POFunction not free-ing in time
      1. USSergey L.
    3. COYou might screw up the memory, at which point `free` might also become unreliable if the metadata is corrupted.
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      1. POFunction not free-ing in time
      1. USDevolus
 

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