9.3 KiB
[support.runtime]
17 Language support library [support]
17.14 Other runtime support [support.runtime]
17.14.1 General [support.runtime.general]
Headers (nonlocal jumps), (signal handling), (variable arguments), and (runtime environment getenv, system), provide further compatibility with C code.
Calls to the functiongetenv ([cstdlib.syn]) shall not introduce a data race ([res.on.data.races]) provided that nothing modifies the environment.
[Note 1:
Calls to the POSIX functionssetenv andputenv modify the environment.
â end note]
A call to the setlocale function may introduce a data race with other calls to the setlocale function or with calls to functions that are affected by the current C locale.
The implementation shall behave as if no library function other than locale::global calls the setlocale function.
17.14.2 Header synopsis [cstdarg.syn]
// all freestanding#define STDC_VERSION_STDARG_H 202311Lnamespace std {using va_list = see below;}#define va_arg(V, P) see below#define va_copy(VDST, VSRC) see below#define va_end(V) see below#define va_start(V, ...) see below
The contents of the header are the same as the C standard library header <stdarg.h>, with the following changes:
-
In lieu of the default argument promotions specified in ISO/IEC 9899:2024 6.5.2.2, the definition in [expr.call] applies.
-
The preprocessing tokens comprising the second and subsequent arguments to va_start (if any) are discarded. [Note 1: va_start accepts a second argument for compatibility with prior revisions of C++. â end note]
See also: ISO/IEC 9899:2024, 7.16
17.14.3 Header synopsis [csetjmp.syn]
#define STDC_VERSION_SETJMP_H 202311Lnamespace std {using jmp_buf = see below; noreturn void longjmp(jmp_buf env, int val);}#define setjmp(env) see below
The contents of the header are the same as the C standard library header <setjmp.h>.
The function signaturelongjmp(jmp_buf jbuf, int val) has more restricted behavior in this document.
A setjmp/longjmp call pair has undefined behavior if replacing the setjmp and longjmp by catch and throw would invoke any non-trivial destructors for any objects with automatic storage duration.
A call to setjmp or longjmp has undefined behavior if invoked in a suspension context of a coroutine ([expr.await]).
See also: ISO/IEC 9899:2024, 7.13
17.14.4 Header synopsis [csignal.syn]
namespace std {using sig_atomic_t = see below; // [support.signal], signal handlersextern "C" using signal-handler = void(int); // exposition onlysignal-handler signal(int sig, signal-handler func); int raise(int sig);}#define SIG_DFL see below#define SIG_ERR see below#define SIG_IGN see below#define SIGABRT see below#define SIGFPE see below#define SIGILL see below#define SIGINT see below#define SIGSEGV see below#define SIGTERM see below
The contents of the header are the same as the C standard library header <signal.h>.
17.14.5 Signal handlers [support.signal]
A call to the function signal synchronizes with any resulting invocation of the signal handler so installed.
A plain lock-free atomic operation is an invocation of a function f from [atomics], such that:
f is the function atomic_is_lock_free(), or
f is the member function is_lock_free(), or
f is a non-static member function of class atomic_flag, or
f is a non-member function, and the first parameter of f has type cv atomic_flag*, or
f is a non-static member function invoked on an object A, such that A.is_lock_free() yields true, or
f is a non-member function, and for every pointer-to-atomic argument A passed to f,atomic_is_lock_free(A) yields true.
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 1: This implicitly excludes the use of new and delete expressions that rely on a library-provided memory allocator. â 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 ([basic.start.dynamic], [stmt.dcl])191 ; or
waiting for the completion of the initialization of a variable with static storage duration ([stmt.dcl]).
A signal handler invocation has undefined behavior if it includes an evaluation that is not signal-safe.
The function signal is signal-safe if it is invoked with the first argument equal to the signal number corresponding to the signal that caused the invocation of the handler.
See also: ISO/IEC 9899:2024, 7.14
Such initialization can occur because it is the first odr-use ([basic.def.odr]) of that variable.