What happens when you try to free() already freed memory in c?

Question

For example:

char * myString = malloc(sizeof(char)*STRING_BUFFER_SIZE);
free(myString);
free(myString);

Are there any adverse side effects

Answer 1

It may crash your program, corrupt memory, or have other more subtle negative effects. After you delete memory, it is a good idea to set it to NULL (0). Trying to free a null pointer does nothing, and is guaranteed to be safe. The same holds true for delete in c++.