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The C++14 Standard, [support.runtime], paragraph 10 [ISO/IEC 14882-2014], states the following:

The common subset of the C and C++ languages consists of all declarations, definitions, and expressions that may appear in a well-formed C++ program and also in a conforming C program. A POF (“plain old function”) is a function that uses only features from this common subset, and that does not directly or indirectly use any function that is not a POF, except that it may use plain lock-free atomic operations. A plain lock-free atomic operation is an invocation of a function f from Clause 29, such that f is not a member function, and either f is the function atomic_is_lock_free, or for every atomic argument A passed to f, atomic_is_lock_free(A) yields true. All signal handlers shall have C linkage. The behavior of any function other than a POF used as a signal handler in a C++ program is implementation-defined.228

Footnote 228 states the following:

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If your signal handler is not a plain old function, then the behavior of a call to it in response to a signal is implementation-defined, at best, and is likely to result in undefined behavior. All signal handlers must meet the definition of a plain old function. In addition to the restrictions placed on signal handlers in a C program, this definition also prohibits the use of features that exist in C++ but not in C (such as non-POD [non–plain old data] objects and exceptions). This includes indirect use of such features through function calls.

In C++17, the wording has changed and relaxed some of the constraints on signal handlers. Section [support.signal], paragraph 3 says:

An evaluation is signal-safe unless it includes one of the following:

— a call to any standard library function, except for plain lock-free atomic operations and functions explicitly identified as signal-safe. [ Note: This implicitly excludes the use of new and delete expressions that rely on a library-provided memory allocator. — end note ]
— an access to an object with thread storage duration;
— a dynamic_cast expression;
— throwing of an exception;
— control entering a try-block or function-try-block;
— initialization of a variable with static storage duration requiring dynamic initialization (6.6.3, 9.7)220; or
— waiting for the completion of the initialization of a variable with static storage duration (9.7).

A signal handler invocation has undefined behavior if it includes an evaluation that is not signal-safe.

Signal handlers in code that will be executed on C++17-compliant platforms must be signal-safe.

Noncompliant Code Example

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