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I'm trying to learn C and I'm currently trying to write a basic stack data structure, but I can't seem to get basic malloc / free right. Here's the code I've been using (I'm just posting a small part here to illustrate a specific problem, not the total code, but the error message was generated just by running this example code in valgrind ) #include <stdio.h> #include <stdlib.h> typedef struct Entry { struct Entry *previous; int value; } Entry; void destroyEntry(Entry entry); int main(int argc, char *argv[]) { Entry* apple; apple = malloc(sizeof(Entry)); destroyEntry(*(apple)); return 0; } void destroyEntry(Entry entry) { Entry *entry_ptr = &entry; free(entry_ptr); return; } When I run it through valgrind with --leak-check=full --track-origins=yes , I get the following error: ==20674== Invalid free() / delete / delete[] / realloc() ==20674== at 0x4028E58: free (vg_replace_malloc.c:427) ==20674== by 0x80485B2: destroyEntry (testing.c:53) ==20674== by 0x8048477: main (testing.c:26) ==20674== Address 0xbecc0070 is on thread 1's stack I think this error means that the destroyEntry function is not allowed to modify memory allocated explicitly in main. Is that right? Why can't I just free the memory I allocated in main in another function? (and is this behavior somehow specific to main?)

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