This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
tgmath.h — type-generic macros
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of
POSIX.1‐2008 defers to the ISO C standard.
header shall include the headers
and shall define several
Of the functions contained within the <math.h>
headers without an f
) suffix, several have one or more parameters
whose corresponding real type is double
. For each such function, except
(), and yn
(), there shall be a corresponding type-generic
macro. The parameters whose corresponding real type is double
function synopsis are generic parameters. Use of the macro invokes a function
whose corresponding real type and type domain are determined by the arguments
for the generic parameters.
Use of the macro invokes a function whose generic parameters have the
corresponding real type determined as follows:
- First, if any argument for generic parameters has type
long double, the type determined is long double.
- Otherwise, if any argument for generic parameters has type
double or is of integer type, the type determined is
- Otherwise, the type determined is float.
For each unsuffixed function in the <math.h>
header for which there
is a function in the <complex.h>
header with the same name except
for a c
prefix, the corresponding type-generic macro (for both
functions) has the same name as the function in the <math.h>
header. The corresponding type-generic macro for fabs
() is fabs
If at least one argument for a generic parameter is complex, then use of the
macro invokes a complex function; otherwise, use of the macro invokes a real
For each unsuffixed function in the <math.h>
header without a
-prefixed counterpart in the <complex.h>
(), and yn
(), the corresponding type-generic macro has the
same name as the function. These type-generic macros are:
| atan2() cbrt() ceil() copysign()
erf() erfc() exp2() expm1() fdim()
|| fma() fmax() fmin() fmod() frexp()
hypot() ilogb() ldexp() lgamma()
|| llround() log10() log1p() log2()
logb() lrint() lround() nearbyint()
|| remainder() remquo() rint() round()
scalbln() scalbn() tgamma() trunc()
If all arguments for generic parameters are real, then use of the macro invokes
a real function; otherwise, use of the macro results in undefined behavior.
For each unsuffixed function in the <complex.h>
header that is not
-prefixed counterpart to a function in the <math.h>
header, the corresponding type-generic macro has the same name as the
function. These type-generic macros are:
carg() cimag() conj()
Use of the macro with any real or complex argument invokes a complex function.
The following sections are informative.
With the declarations:
long double ld;
float complex fc;
double complex dc;
long double complex ldc;
functions invoked by use of type-generic macros are shown in the following
||exp(n), the function
||sin(d), the function
||remainder(n, n), the function
||nextafter(d, f), the function
||carg(n), the function
||creal(d), the function
||carg(dc), the function
Type-generic macros allow calling a function whose type is determined by the
argument type, as is the case for C operators such as '+'
. For example, with a type-generic cos
() macro, the
) will have type float
This feature enables writing more portably efficient code and alleviates need
for awkward casting and suffixing in the process of porting or adjusting
precision. Generic math functions are a widely appreciated feature of Fortran.
The only arguments that affect the type resolution are the arguments
corresponding to the parameters that have type double
in the synopsis.
Hence the type of a type-generic call to nexttoward
(), whose second
parameter is long double
in the synopsis, is determined solely by the
type of the first argument.
The term ``type-generic'' was chosen over the proposed alternatives of intrinsic
and overloading. The term is more specific than intrinsic, which already is
widely used with a more general meaning, and reflects a closer match to
Fortran's generic functions than to C++ overloading.
The macros are placed in their own header in order not to silently break old
programs that include the <math.h>
header; for example, with:
, double *
) is excluded because no way was seen
to make it safe without complicating the type resolution.
The implementation might, as an extension, endow appropriate ones of the macros
that POSIX.1‐2008 specifies only for real arguments with the ability to
invoke the complex functions.
POSIX.1‐2008 does not prescribe any particular implementation mechanism
for generic macros. It could be implemented simply with built-in macros. The
generic macro for sqrt
(), for example, could be implemented with:
#define sqrt(x) __BUILTIN_GENERIC_sqrt(x)
Generic macros are designed for a useful level of consistency with C++
overloaded math functions.
The great majority of existing C programs are expected to be unaffected when the
header is included instead of the
headers. Generic macros are
similar to the ISO/IEC 9899:1999 standard library masking macros,
though the semantic types of return values differ.
The ability to overload on integer as well as floating types would have been
useful for some functions; for example, copysign
(). Overloading with
different numbers of arguments would have allowed reusing names; for example,
() for remquo
(). However, these facilities would have
complicated the specification; and their natural consistent use, such as for a
() or a two-argument atan
(), would have introduced
further inconsistencies with the ISO/IEC 9899:1999 standard for
The ISO C standard in no way limits the implementation's options for
efficiency, including inlining library functions.
The System Interfaces volume of POSIX.1‐2008, cabs()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
7, Copyright (C) 2013 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013
Technical Corrigendum 1 applied.) In the event of any discrepancy between this
version and the original IEEE and The Open Group Standard, the original IEEE
and The Open Group Standard is the referee document. The original Standard can
be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely
to have been introduced during the conversion of the source files to man page
format. To report such errors, see