cppreference.com > Standard C Memory > free free Syntax:
      #include <stdlib.h>
      void free( void* ptr );
The free() function deallocates the space pointed to by ptr, freeing it up for future use. ptr must have been used in a previous call to malloc(), calloc(), or realloc(). An example:
       typedef struct data_type {
         int age;
         char name[20];
       } data;

       data *willy;
       willy = (data*) malloc( sizeof(*willy) );
       ...
       free( willy );
Related topics: calloc (C/C++ Keywords) delete malloc (C/C++ Keywords) new realloc