Replacement functions - cppreference.com (original) (raw)

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.

[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 #include #include   // 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: