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POmalloc() struct in a function, free() before ending program
 

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  1. POmalloc() struct in a function, free() before ending program
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    <p>I am learning the basics of C, and now working with malloc(). Say I have a function that asks the user for input, populates a structure with said data, and that structure in saved in an array (all passed by reference from a main function).</p> <p>I ran the program through Valgrind, I get the "still reachable" bytes (which should be ok right? not considered a leak), but any data saved I get lost blocks.</p> <p>How would I go freeing that memory after the program has finished running? Also I have some (2) questions within the code just to clarify some things and would appreciate if someone could explain them to me.</p> <p>Here is some code similar to what I am trying to do:</p> <p>I have the following struct declared: </p> <pre><code>struct Person { char name[MAX_INPUT]; int age; }; </code></pre> <p>I am writing a function that goes like this:</p> <pre><code>int function2(struct Person *list, int *index) { struct Person *prsn = malloc(sizeof(struct Person)); // !Why do we sometimes cast the malloc or not? // I sometimes get errors when I do, sometimes when I don't, // while the surrounding code is pretty much the same. assert(prsn != NULL); // User input code goes here ... // Now to save the Person created strcpy(prsn-&gt;name, nameInput); prsn-&gt;age = ageInput; list[(*index)++] = *prsn; // !Why use the dereferencing *prsn here? // why not directly prsn? Or is that saving the memory address and not very useful. return 0; } </code></pre> <p>And this is my main function:</p> <pre><code>int main(int argc, char *argv[]) { struct Person personList[MAX_SIZE]; int index; function2(personList, &amp;index); // Before closing, I want to free any mallocs I have done here. free() return 0; } </code></pre> <p>Valgrind report:</p> <pre><code>LEAK SUMMARY: ==1766== definitely lost: 44 bytes in 1 blocks ==1766== indirectly lost: 0 bytes in 0 blocks ==1766== possibly lost: 0 bytes in 0 blocks ==1766== still reachable: 10,355 bytes in 34 blocks ==1766== suppressed: 0 bytes in 0 blocks </code></pre> <p>Thank you in advance.</p> <p>Edit: Fixed function2 parameters, return and other things. I apologize, was writing it quickly to illustrate my main question about freeing memory. Thanks for the corrections tips, but the real code is actually compiling correctly and everything.</p> <p>Edit2: After adding a simple loop at the end of main like suggested to use free(), I get the following errors.</p> <pre><code>==2216== LEAK SUMMARY: ==2216== definitely lost: 44 bytes in 1 blocks ==2216== indirectly lost: 0 bytes in 0 blocks ==2216== possibly lost: 0 bytes in 0 blocks ==2216== still reachable: 10,355 bytes in 34 blocks ==2216== suppressed: 0 bytes in 0 blocks ==2216== ==2216== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0) ==2216== ==2216== 1 errors in context 1 of 2: ==2216== Invalid free() / delete / delete[] / realloc() ==2216== at 0x563A: free (in /usr/local/Cellar/valgrind/3.8.1/lib/valgrind/vgpreload_memcheck-amd64-darwin.so) ==2216== by 0x10000194E: main (in ./test.out) ==2216== Address 0x7fff5fbf9dd0 is on thread 1's stack ==2216== ==2216== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0) </code></pre>
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    1. COHow many parameters does `function2` accept?
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    2. COYou never `free` the allocated `struct Person *prsn = malloc(sizeof(struct Person));` in `function2`.
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      1. POmalloc() struct in a function, free() before ending program
      1. USDaniel Fischer
    3. COYou need a semicolon after the struct definition.
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      1. USwildplasser
 

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