Certain functions for which a definition is supplied by the implementation arereplaceable . A C++ program may provide a definition with thesignature of a replaceable function, called areplacement 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 notinline.
• It isattached 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 astandard 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

#include <cstddef>#include <new>#include <print> // replacement functionvoid*operator new(std::size_t count){std::print("Replaced!");return nullptr;} int main(){int* ptr= newint;// invokes the replacement version defined by the program}

Replaced!

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