9.16.1 Real-Type Determination

Use of the macro invokes a function whose generic parameters have the corresponding real type determined as follows:

1. First, if any argument for generic parameters has type long double , the type determined is long double .
2. Otherwise, if any argument for generic parameters has type double or is of integer type, the type determined is double .
3. Otherwise, the type determined is float .

9.16.2 Unsuffixed Functions in (<math.h>) and (<complex.h>) with the Same Name

For each unsuffixed function in <math.h> for which there is a function in <complex.h> 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 <math.h> . The corresponding type-generic macro for fabs and cabs is fabs . These functions are:

<math.h> <complex.h> type-generic function function 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.

9.16.3 Unsuffixed Functions in (<math.h>) with no c-prefixed Counterpart in (<complex.h>)

For each unsuffixed function in <math.h> without a c-prefixed counterpart in <complex.h> , 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 scalbn erfc hypot lrint scalbln 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.

9.16.4 Unsuffixed Functions in (<complex.h>) that are not c-prefixed Counterparts to Functions in (<math.h>)

For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a function in <math.h> , the corresponding type-generic macro has the same name as the function:

carg conj creal cimag cproj

Use of the macro with any real or complex argument invokes a complex function.

9.16.5 Example

Consider the following declarations:

#include <tgmath.h> int n; float f; double d; long double ld; float complex fc; double complex dc; long double complex ldc;

Given these declarations, functions invoked by use of type-generic macros are as follows:

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)

9.16.6 Imaginary Arguments

Type-generic macros that accept complex arguments also accept imaginary arguments. If an argument is imaginary, the macro expands to an expression whose type is real, imaginary, or complex, as appropriate for the particular function: if the argument is imaginary, then the types of cos , cosh , fabs , carg , cimag , and creal are real; the types of sin , tan , sinh , tanh , asin , atan , asinh , and atanh are imaginary; and the types of the others are complex.

Given an imaginary argument, each of the type-generic macros cos , sin , tan , cosh , sinh , tanh , asin , atan , asinh , atanh is specified by a formula in terms of real functions:

cos(iy) = cosh(y) sin(iy) = i sinh(y) tan(iy) = i tanh(y) cosh(iy) = cos(y) sinh(iy) = i sin(y) tanh(iy) = i tan(y) asin(iy) = i asinh(y) atan(iy) = i atanh(y) asinh(iy) = i asin(y) atanh(iy) = i atan(y)

9.17 Date and Time (<time.h>)

The <time.h> header file defines two macros, and declares four types and several functions for manipulating time and date information. Some functions process local time, which may differ from calendar time because of time zone.

Types

size_t

An unsigned integral type of the result of the sizeof operator.

clock_t time_t

Arithmetic types capable of representing times.

struct tm

Holds the components of a calendar time, called the broken-down time. The structure contains the following members:

int tm_sec; /* seconds after the minute -- [0,61] */ int tm_min; /* minutes after the hour -- [0,59] */ int tm_hour; /* hours since midnight -- [0,23] */ int tm_mday; /* day of the month -- [1,31] */ int tm_mon; /* months since January -- [0,11] */ int tm_year; /* years since 1900 */ int tm_wday; /* days since Sunday -- [0,6] */ int tm_yday; /* days since January 1 -- [0,365] */ int tm_isdst; /* Daylight Saving Time flag -- 0 if */ /* DST not in effect; positive if it is; */ /* negative if information is not available. */

Macros

NULL

Expands to an implementation-defined null pointer constant.

CLOCKS_PER_SEC

The number per second of the value returned by the clock function.

Time Conversion Functions

char *asctime(const struct tm *timeptr);

Converts a broken-down time in the structure pointed to by timeptr into a 26-character string in the form of this example:

Sat Sep 08 08:10:32 1990\n\0

A pointer to the string is returned.

char *ctime(const time_t *timer);

Converts the calendar time pointed to by timer to local time in a string of the form generated by the asctime function. A pointer to the string is returned. The ctime function is equivalent to the following:

asctime(localtime(timer))

struct tm *gmtime(const time_t *timer);

Converts the calendar time pointed to by timer into a broken-down time expressed as Coordinated Universal Time (UTC). The gmtime function returns a pointer to the broken-down time, or a null pointer if UTC is not available.

struct tm *localtime(const time_t *timer);

Converts the calendar time pointed to by timer into a broken-down time expressed as local time. The localtime function returns a pointer to the broken-down time.

size_t strftime(char *s, size_t maxsize, const char *format, const struct tm *timeptr);

Places characters into the array pointed to by s as controlled by the string pointed to by format. The format string consists of zero or more conversion specifiers and ordinary multibyte characters. All ordinary multibyte characters (including the terminating null character) are copied unchanged into the array. Each conversion specifier is replaced by the appropriate characters as shown in Table 9-2. The appropriate characters are determined by the LC_TIME category of the current locale and by the values contained in the structure pointed to by timeptr.

Table 9-2 strftime Conversion Specifiers

Specifier	Replaced by
%a	The locale's abbreviated weekday name
%A	The locale's full weekday name
%b	The locale's abbreviated month name
%B	The locale's full month name
%c	The locale's appropriate date and time representation
%d	The day of the month as a decimal number (01 -- 31)
%H	The hour (24-hour clock) as a decimal number (00 -- 23)
%I	The hour (12-hour clock) as a decimal number (01 -- 12)
%j	The day of the year as a decimal number (001 -- 366)
%m	The month as a decimal number (01 -- 12)
%M	The minute as a decimal number (00 -- 59)
%p	The locale's equivalent of the AM/PM designations associated with a 12-hour clock
%S	The second as a decimal number (00 -- 61)
%U	The week number of the year (the first Sunday as the first day of week 1) as a decimal number (00 -- 53)
%w	The weekday as a decimal number (0 [Sunday] -- 6)
%W	The week number of the year (the first Monday as the first day of week 1) as a decimal number (00 -- 53)
%x	The locale's appropriate date representation
%X	The locale's appropriate time representation
%y	The year without century as a decimal number (00 -- 99)
%Y	The year with century as a decimal number
%Z	The time zone name or abbreviation, or by no characters if no time zone can be determined
%%	%

If the total number of resulting characters including the terminating null character is not more than maxsize , the strftime function returns the number of characters placed into the array pointed to by s, not including the terminating null character. Otherwise, 0 is returned, and the array contents are indeterminate.

Time Manipulation Functions

clock_t clock(void);

Determines the processor time used. The clock function returns the processor time used by the program since the beginning of an event related to the program invocation. To determine the time in seconds, divide the return value by the value of the CLOCKS_PER_SEC macro. If the processor time is not available or cannot be represented, the value returned is (clock_t)-1 . (To measure the time spent in a program, call the clock function at the start of the program and subtract the return value from that of subsequent calls.)

double difftime(time_t time1, time_t time0);

Returns the difference between the two calendar times time1 and time0, expressed in seconds, as a double .

time_t mktime(struct tm*timeptr);

Converts the broken-down time, expressed as local time, in the structure pointed to by timeptr into a calendar time value with the same encoding as that of the values returned by the time function (that is, a value of type time_t ), which it returns. If the calendar time cannot be represented, the value (time_t)-1 is returned.
The original values of the tm_wday and tm_yday time components are ignored, and the original values of the other components are not restricted to the ranges indicated in the previous discussion of struct_tm . Upon successful completion of the function, the values of the tm_wday and tm_yday components are set appropriately, and the other components are set to represent the specified calendar time, but with their values forced to the ranges indicated in the discussion of struct_tm . The final value of tm_wday is not set until tm_mon and tm_year are determined.

time_t time(time_t *timer);

Returns the current calendar time. If the calendar time is not available, the value (time_t)-1 is returned.