std::free
<cstdlib>
Deallocates the space previously allocated by std::malloc , std::calloc , std::aligned_alloc (since C++17), or std::realloc .
If ptr is a null pointer, the function does nothing.
The behavior is undefined if the value of ptr does not equal a value returned earlier by std::malloc , std::calloc , std::aligned_alloc (since C++17), or std::realloc .
The behavior is undefined if the memory area referred to by ptr has already been deallocated, that is, std::free or std::realloc has already been called with ptr as the argument and no calls to std::malloc , std::calloc , std::aligned_alloc (since C++17), or std::realloc resulted in a pointer equal to ptr afterwards.
The behavior is undefined if after std::free returns, an access is made through the pointer ptr (unless another allocation function happened to result in a pointer value equal to ptr).
The following functions are required to be thread-safe:
- The library versions of operator new and operator delete
- User replacement versions of global operator new and operator delete
- std::calloc , std::malloc , std::realloc , std::aligned_alloc (since C++17), std::free
Calls to these functions that allocate or deallocate a particular unit of storage occur in a single total order, and each such deallocation call happens-before the next allocation (if any) in this order.
(since C++11)Contents
[edit] Parameters
[edit] Return value
(none)
[edit] Notes
The function accepts (and does nothing with) the null pointer to reduce the amount of special-casing. Whether allocation succeeds or not, the pointer returned by an allocation function can be passed to std::free.
[edit] Example
#include <cstdlib> int main() { int* p1 = (int*)std::malloc (10 * sizeof *p1); std::free(p1); // every allocated pointer must be freed int* p2 = (int*)std::calloc (10, sizeof *p2); int* p3 = (int*)std::realloc (p2, 1000 * sizeof *p3); if (!p3) // p3 null means realloc failed and p2 must be freed. std::free(p2); std::free(p3); // p3 can be freed whether or not it is null. }