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PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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tgmath.h(0P) POSIX Programmer's Manual tgmath.h(0P)
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
#include <tgmath.h>
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.1‐2017 defers to the ISO C standard.
The <tgmath.h> header shall include the headers <math.h> and
<complex.h> and shall define several type-generic macros.
Of the functions contained within the <math.h> and <complex.h>
headers without an f (float) or l (long double) suffix, several
have one or more parameters whose corresponding real type is
double. For each such function, except modf(), j0(), j1(), jn(),
y0(), y1(), and yn(), there shall be a corresponding type-generic
macro. The parameters whose corresponding real type is double in
the 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 double.
* 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() and cabs()
is fabs().
┌───────────────────┬──────────────────────┬────────────────────┐
│ <math.h> Function │ <complex.h> Function │ Type-Generic Macro │
├───────────────────┼──────────────────────┼────────────────────┤
│ acos() │ cacos() │ acos() │
│ asin() │ casin() │ asin() │
│ atan() │ catan() │ atan() │
│ acosh() │ cacosh() │ acosh() │
│ asinh() │ casinh() │ asinh() │
│ atanh() │ catanh() │ atanh() │
│ cos() │ ccos() │ cos() │
│ sin() │ csin() │ sin() │
│ tan() │ ctan() │ tan() │
│ cosh() │ ccosh() │ cosh() │
│ sinh() │ csinh() │ sinh() │
│ tanh() │ ctanh() │ tanh() │
│ exp() │ cexp() │ exp() │
│ log() │ clog() │ log() │
│ pow() │ cpow() │ pow() │
│ sqrt() │ csqrt() │ sqrt() │
│ fabs() │ cabs() │ 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 function.
For each unsuffixed function in the <math.h> header without a c-
prefixed counterpart in the <complex.h> header, except for modf(),
j0(), j1(), jn(), y0(), y1(), and yn(), the corresponding type-
generic macro has the same name as the function. These type-
generic macros are:
atan2() fma() llround() remainder()
cbrt() fmax() log10() remquo()
ceil() fmin() log1p() rint()
copysign() fmod() log2() round()
erf() frexp() logb() scalbln()
erfc() hypot() lrint() scalbn()
exp2() ilogb() lround() tgamma()
expm1() ldexp() nearbyint() trunc()
fdim() lgamma() nextafter()
floor() llrint() nexttoward()
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
a c-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() cproj() creal()
Use of the macro with any real or complex argument invokes a
complex function.
The following sections are informative.
With the declarations:
#include <tgmath.h>
int n;
float f;
double d;
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 table:
┌──────────────────┬───────────────────────────────┐
│ Macro │ Use Invokes │
├──────────────────┼───────────────────────────────┤
│ exp(n) │ exp(n), the function │
│ acosh(f) │ acoshf(f) │
│ sin(d) │ sin(d), the function │
│ atan(ld) │ atanl(ld) │
│ log(fc) │ clogf(fc) │
│ sqrt(dc) │ csqrt(dc) │
│ pow(ldc,f) │ cpowl(ldc, f) │
│ remainder(n,n) │ remainder(n, n), the function │
│ nextafter(d,f) │ nextafter(d, f), the function │
│ nexttoward(f,ld) │ nexttowardf(f, ld) │
│ copysign(n,ld) │ copysignl(n, ld) │
│ ceil(fc) │ Undefined behavior │
│ rint(dc) │ Undefined behavior │
│ fmax(ldc,ld) │ Undefined behavior │
│ carg(n) │ carg(n), the function │
│ cproj(f) │ cprojf(f) │
│ creal(d) │ creal(d), the function │
│ cimag(ld) │ cimagl(ld) │
│ cabs(fc) │ cabsf(fc) │
│ carg(dc) │ carg(dc), the function │
│ cproj(ldc) │ cprojl(ldc) │
└──────────────────┴───────────────────────────────┘
Type-generic macros allow calling a function whose type is
determined by the argument type, as is the case for C operators
such as '+' and '*'. For example, with a type-generic cos()
macro, the expression cos((float)x) 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:
printf ("%e", sin(x))
modf(double, 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:
#undef sqrt
#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 <tgmath.h> header is included instead of the
<math.h> or <complex.h> 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, remainder() for remquo(). However,
these facilities would have complicated the specification; and
their natural consistent use, such as for a floating abs() or a
two-argument atan(), would have introduced further inconsistencies
with the ISO/IEC 9899:1999 standard for insufficient benefit.
The ISO C standard in no way limits the implementation's options
for efficiency, including inlining library functions.
None.
math.h(0p), complex.h(0p)
The System Interfaces volume of POSIX.1‐2017, cabs(3p), fabs(3p),
modf(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 tgmath.h(0P)
Pages that refer to this page: nextafter(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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