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POWhy does malloc allocate a different number of bytes than requested?
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copied!<p>I have this piece of code</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <stdint.h> #include <string.h> int main(){ void *a, *b; a = malloc(16); b = malloc(16); printf("\n block size (for a): %p-%p : %li", b, a, b-a); a = malloc(1024); b = malloc(1024); printf("\n block size (for a): %p-%p : %li", b, a, b-a); } </code></pre> <p>Shouldn't this print the last allocated block size (16 or 1024)? It instead prints 24 and 1032, so the amount of memory allocated seems to have 8 extra bytes.</p> <p>My problem is (before making this test case) that I do <code>malloc()</code> in a function (1024 bytes), and return the allocated result. When checking the block size on the function return I get 516 blocks... and I don't understand why. I guess this might be the reason for the memory corruption that occurs after doing some processing on the allocated buffers:)</p> <p><b>Edit:</b> I've seen <a href="https://stackoverflow.com/questions/232691/array-size-from-pointer-in-c">How can I get the size of an array from a pointer in C?</a> and seems to ask the same thing, sorry for reposting.</p> <p>I've redone my example to my more specific code:</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <stdint.h> #include <string.h> short int * mallocStuff(long int number, short int base){ short int *array; int size=1024; array=(short int*)calloc(1,size); //array=(short int*)malloc(size); return array; } int main(){ short int **translatedArray; translatedArray=malloc(4*sizeof(short int)); int i; for(i=0;i<4;i++){ translatedArray[i]=mallocStuff(0,0); if(i>0) printf("\n block size (for a): %p-%p : %i", translatedArray[i], translatedArray[i-1], translatedArray[i]-translatedArray[i-1]); } return 0; } </code></pre> <p>And the output is</p> <pre><code> block size (for a): 0x804a420-0x804a018 : 516 block size (for a): 0x804a828-0x804a420 : 516 block size (for a): 0x804ac30-0x804a828 : 516 </code></pre> <p>According to the above post that is bigger than 1024. Am I wrong?</p>

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