Replacement functions
noexcept specifier (C++11)Certain functions for which a definition is supplied by the implementation are replaceable . A C++ program may provide a definition with the signature of a replaceable function, called a replacement function . The replacement function, if provided, is used instead of the default version supplied by the implementation. Such replacement occurs prior to program startup.
If a declaration of the replacement function does not satisfy any of the following conditions, the program is ill-formed, no diagnostic is required:
- It is not inline.
- It is attached to the global module.
- It has C++ language linkage.
- It has the same return type as the replaceable function.
- If the replaceable function is declared in a standard library header, it would be valid as a redeclaration of the declaration in that header.
Core language
It is implementation-defined whether the contract-violation handler ::handle_contract_violation is replaceable.
(since C++26)[edit] Standard library
The following standard library functions are replaceable, and the description of function semantics apply to both the default version defined by the C++ standard library and the replacement function defined by the program:
[edit] Example
Uses a replacement allocation function:
#include <cstddef> #include <new> #include <print> // replacement function void* operator new (std::size_t count) { std::print ("Replaced!"); return nullptr; } int main() { int* ptr = new int; // invokes the replacement version defined by the program }
Output:
Replaced!