The facilities of the Standard C Library are provided in 18 additional headers, as shown in Table 3:
<cassert> <ciso646> <csetjmp> <cstdio> <ctime>
<cctype> <climits> <csignal> <cstdlib> <cwchar>
<cerrno> <clocale> <cstdarg> <cstring> <cwctype>
<cfloat> <cmath> <cstddef>
Except [...] , the contents of each header cname shall be the same as that of the corresponding header name.h [...]. In the C++ Standard library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope of the namespace std.
Names which are defined as macros in C shall be defined as macros in the C++ Standard library, even if license is granted in C for implementation as functions.
Each C header, whose name has the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the namespace scope of the namespace std and is followed by an explicit using-declaration.
Example: The header <cstdlib> provides its declarations and definitions within the namespace std. The header <stdlib.h> makes these available in the global name space, much as in the C Standard.