Free memory allocated in a different function?
c, free, malloc, memory-management, pointers
Solution
Whenever you pass a parameter to a function, a copy is made, and the function works on that copy. So in your case, you are trying to `free` a copy of the original object, which doesn't make any sense.
You should modify your function to take a pointer, and then you can have it call `free` directly on that pointer.
Problem
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?)