Resizing memory in a separate function causes a memory leak.
Separated into two functions and leaky:
#include <stdio.h>
#include <stdlib.h>
void memo(int* list);
int main (void)
{
int* list = malloc(sizeof(int));
memo(list);
free(list);
}
void memo(int* list)
{
int bigger = 5;
int* temp;
temp = realloc(list, sizeof(int)*bigger);
if(temp == NULL)
{
exit(1);
}
list = temp;
}
Combined into one function and not leaky:
#include <stdio.h>
#include <stdlib.h>
int main (void)
{
int* list = malloc(sizeof(int));
int bigger = 5;
int* temp;
temp = realloc(list, sizeof(int)*bigger);
if(temp == NULL)
{
exit(1);
}
list = temp;
free(list);
}
I'm writing a program that creates an int array with malloc(). Then, in another function, I expand the original array with realloc(), then free the array with free() in the original function. This gives me a memory leak according to valgrind. This doesn't happen however if I make them one function---which is fine for this simplified demo, but would make things very messy in my actual program. Is it possible that free() is freeing the amount of blocks the original malloc() called and not the new size of the memory block as specified in the other function?
For reference, here is the output for the leaky program in valgrind.
> ==323== Memcheck, a memory error detector
> ==323== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
> ==323== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
> ==323== Command: ./a.out
> ==323==
> ==323== Invalid free() / delete / delete\[\] / realloc()
> ==323== at 0x483CA3F: free (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x40118A: main (smem.c:10)
> ==323== Address 0x4a4a040 is 0 bytes inside a block of size 4 free'd
> ==323== at 0x483DFAF: realloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x4011C9: memo (smem.c:17)
> ==323== by 0x40117E: main (smem.c:9)
> ==323== Block was alloc'd at
> ==323== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x401171: main (smem.c:8)
> ==323==
> ==323==
> ==323== HEAP SUMMARY:
> ==323== in use at exit: 20 bytes in 1 blocks
> ==323== total heap usage: 2 allocs, 2 frees, 24 bytes allocated
> ==323==
> ==323== 20 bytes in 1 blocks are definitely lost in loss record 1 of 1
> ==323== at 0x483DFAF: realloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x4011C9: memo (smem.c:17)
> ==323== by 0x40117E: main (smem.c:9)
> ==323==
> ==323== LEAK SUMMARY:
> ==323== definitely lost: 20 bytes in 1 blocks
> ==323== indirectly lost: 0 bytes in 0 blocks
> ==323== possibly lost: 0 bytes in 0 blocks
> ==323== still reachable: 0 bytes in 0 blocks
> ==323== suppressed: 0 bytes in 0 blocks
> ==323==
> ==323== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
> ==323==
> ==323== 1 errors in context 1 of 2:
> ==323== Invalid free() / delete / delete\[\] / realloc()
> ==323== at 0x483CA3F: free (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x40118A: main (smem.c:10)
> ==323== Address 0x4a4a040 is 0 bytes inside a block of size 4 free'd
> ==323== at 0x483DFAF: realloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x4011C9: memo (smem.c:17)
> ==323== by 0x40117E: main (smem.c:9)
> ==323== Block was alloc'd at
> ==323== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==323== by 0x401171: main (smem.c:8)
> ==323==
> ==323== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
