16 Library introduction [library]

16.2 The C standard library [library.c]

The C++ standard library also makes available the facilities of the C standard library, suitably adjusted to ensure static type safety.
The descriptions of many library functions rely on the C standard library for the semantics of those functions.
In some cases, the signatures specified in this document may be different from the signatures in the C standard library, and additional overloads may be declared in this document, but the behavior and the preconditions (including any preconditions implied by the use of a C restrict qualifier) are the same unless otherwise stated.
A call to a C standard library function is a non-constant library call ([defns.nonconst.libcall]) if it raises a floating-point exception other than FE_INEXACT.
The semantics of a call to a C standard library function evaluated as a core constant expression are those specified in ISO/IEC 9899:2018, Annex F135 to the extent applicable to the floating-point types ([basic.fundamental]) that are parameter types of the called function.
[Note 1: 
ISO/IEC 9899:2018, Annex F specifies the conditions under which floating-point exceptions are raised and the behavior when NaNs and/or infinities are passed as arguments.
— end note]
[Note 2: 
Equivalently, a call to a C standard library function is a non-constant library call if errno is set when math_errhandling & MATH_ERRNO is true.
— end note]
135)135)
See also ISO/IEC 9899:2018, 7.6.