Annex D (normative) Compatibility features [depr]

D.6 C standard library headers [depr.c.headers]

For compatibility with the C standard library, the C++ standard library provides the C headers shown in Table 136.
Table 136 — C headers
<assert.h>
<inttypes.h>
<signal.h>
<stdio.h>
<wchar.h>
<complex.h>
<iso646.h>
<stdalign.h>
<stdlib.h>
<wctype.h>
<ctype.h>
<limits.h>
<stdarg.h>
<string.h>
<errno.h>
<locale.h>
<stdbool.h>
<tgmath.h>
<fenv.h>
<math.h>
<stddef.h>
<time.h>
<float.h>
<setjmp.h>
<stdint.h>
<uchar.h>

D.6.1 Header <complex.h> synopsis [depr.complex.h.syn]

#include <complex>
The header <complex.h> behaves as if it simply includes the header <complex> ([complex.syn]).
[Note
:
Names introduced by <complex> in namespace std are not placed into the global namespace scope by <complex.h>.
end note
]

D.6.2 Header <iso646.h> synopsis [depr.iso646.h.syn]

The C++ header <iso646.h> is empty.
[Note
:
and, and_­eq, bitand, bitor, compl, not_­eq, not, or, or_­eq, xor, and xor_­eq are keywords in this International Standard ([lex.key]).
end note
]

D.6.3 Header <stdalign.h> synopsis [depr.stdalign.h.syn]

#define __alignas_is_defined 1
The contents of the C++ header <stdalign.h> are the same as the C standard library header <stdalign.h>, with the following changes: The header <stdalign.h> does not define a macro named alignas.
See also: ISO C 7.15

D.6.4 Header <stdbool.h> synopsis [depr.stdbool.h.syn]

#define __bool_true_false_are_defined 1
The contents of the C++ header <stdbool.h> are the same as the C standard library header <stdbool.h>, with the following changes: The header <stdbool.h> does not define macros named bool, true, or false.
See also: ISO C 7.18

D.6.5 Header <tgmath.h> synopsis [depr.tgmath.h.syn]

#include <cmath>
#include <complex>
The header <tgmath.h> behaves as if it simply includes the headers <cmath> ([cmath.syn]) and <complex> ([complex.syn]).
[Note
:
The overloads provided in C by type-generic macros are already provided in <complex> and <cmath> by “sufficient” additional overloads.
end note
]
[Note
:
Names introduced by <cmath> or <complex> in namespace std are not placed into the global namespace scope by <tgmath.h>.
end note
]

D.6.6 Other C headers [depr.c.headers.other]

Every C header other than <complex.h>, <iso646.h>, <stdalign.h>, <stdbool.h>, and <tgmath.h>, each of which has a name of the form <name.h>, behaves as if each name placed in the standard library namespace by the corresponding <cname> header is placed within the global namespace scope, except for the functions described in [sf.cmath], the declaration of std::byte ([cstddef.syn]), and the functions and function templates described in [support.types.byteops].
It is unspecified whether these names are first declared or defined within namespace scope ([basic.scope.namespace]) of the namespace std and are then injected into the global namespace scope by explicit using-declarations.
[Example
:
The header <cstdlib> assuredly provides its declarations and definitions within the namespace std.
It may also provide these names within the global namespace.
The header <stdlib.h> assuredly provides the same declarations and definitions within the global namespace, much as in the C Standard.
It may also provide these names within the namespace std.
end example
]