How to find the commit that erase a change

Hi,

I have a file which contains complicated change history. When I use
    git log -p file
to see all changes made in this file, I found that a change disappeared
for no reason.

For example, I made following change in a commit:

@@ -2,3 +2,8 @@ int main(void)
 {
        printf("hello world");
 }
+
+func(void)
+{
+       printf("a func");
+}

But when I open this file of latest version, I found the above change is
disappeared. So I decide use
    git log -p file
to see which commit erase my change. But I doesn't see any commit which
contains changes like following:

@@ -2,8 +2,3 @@ int main(void)
 {
        printf("hello world");
 }
-
-func(void)
-{
-       printf("a func");
-}

So, how to find the commit that erase my change?

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