Declaring a function with C linkage
Question
What declaration makes a C++ function callable with C linkage?
Short answer
Prefix it with extern "C", e.g. extern "C" double f(double);, or wrap several declarations in extern "C" { ... }. This switches off C++ name mangling so C code or other languages can link to it; such functions cannot be overloaded. Headers shared with C usually guard the block with #ifdef __cplusplus.
Adapted from Joshi, Denson & Downes, Quant Job Interview Questions and Answers, Q7.35, p.233; question and answer rewritten by SelfMadeQuant.com.
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