The time header provides several functions useful for reading and converting the current time and date. Some functions behavior is defined by the LC_TIME category of the location setting.
asctime();
clock();
ctime();
difftime();
gmtime();
localtime();
mktime();
strftime();
time();
asctime
Declaration:
char *asctime(const struct tm *timeptr);
Returns a pointer to a string which represents the day and time of the structure timeptr.
clock
Declaration:
clock_t clock(void);
Returns the processor clock time used since the beginning of an implementation-defined era (normally the beginning of the program). The returned value divided by CLOCKS_PER_SEC results in the number of seconds.
ctime
Declaration:
char *ctime(const time_t *timer);
Returns a string representing the localtime based on the argument timer.
difftime
Declaration:
double difftime(time_t time1, time_t time2);
Calculates the difference of seconds between time1 and time2 (time1-time2).
Returns the number of seconds.
gmtime
Declaration:
struct tm *gmtime(const time_t *timer);
The value of timer is broken up into the structure tm and expressed in Coordinated Universal Time (UTC) also known as Greenwich Mean Time (GMT).
A pointer to the structure is returned. A null pointer is returned if UTC is not available.
localtime
Declaration:
struct tm *localtime(const time_t *timer);
The value of timer is broken up into the structure tm and expressed in the local time zone.
A pointer to the structure is returned.
mktime
Declaration:
time_t mktime(struct tm *timeptr);
Converts the structure pointed to by timeptr into a time_t value according to the local time zone. The values in the structure are not limited to their constraints. If they exceed their bounds, then they are adjusted accordingly so that they fit within their bounds. The original values of tm_wday (day of the week) and tm_yday (day of the year) are ignored, but are set correctly after the other values have been constrained. tm_mday (day of the month) is not corrected until after tm_mon and tm_year are corrected.
After adjustment the structure still represents the same time.
strftime
Declaration:
size_t strftime(char *str, size_t maxsize, const char *format, const struct tm *timeptr);
Formats the time represented in the structure timeptr according to the formatting rules defined in format and stored into str. No more than maxsize characters are stored into str (including the terminating null character).
All characters in the format string are copied to the str string, including the terminating null character, except for conversion characters. A conversion character begins with the % sign and is followed by another character which defines a special value that it is to be replaced by. Conversion
Character What it is replaced by
%a abbreviated weekday name
%A full weekday name
%b abbreviated month name
%B full month name
%c appropriate date and time representation
%d day of the month (01-31)
%H hour of the day (00-23)
%I hour of the day (01-12)
%j day of the year (001-366)
%m month of the year (01-12)
%M minute of the hour (00-59)
%p AM/PM designator
%S second of the minute (00-61)
%U week number of the year where Sunday is the first day of week 1 (00-53)
%w weekday where Sunday is day 0 (0-6)
%W week number of the year where Monday is the first day of week 1 (00-53)
%x appropriate date representation
%X appropriate time representation
%y year without century (00-99)
%Y year with century
%Z time zone (possibly abbreviated) or no characters if time zone isunavailable
%% %
Returns the number of characters stored into str not including the terminating null character. On error zero is returned.
math.h
Trigonometric Functions
acos
asin
atan
atan2
cos
cosh
sin
sinh
tan
tanh
Exponential, Logarithmic, and Power Functions
exp
frexp
ldexp
log
log10
modf
pow
sqrt
Other Math Functions
ceil
fabs
floor
fmod
string.h
memchr
memcmp
memcpy
memmove
memset
strcat
strncat
strchr
strncmp
strcoll
strcpy
strncpy
strcspn
strerror
strlen
strpbrk
strrchr
strspn
strstr
strtok
strxfrm
memchr
Declaration:
void *memchr(const void *str, int c, size_t n);
Searches for the first occurrence of the character c (an unsigned char) in the first n bytes of the string pointed to by the argument str.
Returns a pointer pointing to the first matching character, or null if no match was found.
memcmp
Declaration:
int memcmp(const void *str1, const void *str2, size_t n);
Compares the first n bytes of str1 and str2. Does not stop comparing even after the null character (it always checks n characters).
Returns zero if the first n bytes of str1 and str2 are equal. Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.
memcpy
Declaration:
void *memcpy(void *str1, const void *str2, size_t n);
Copies n characters from str2 to str1. If str1 and str2 overlap the behavior is undefined.
Returns the argument str1.
memmove
Declaration:
void *memmove(void *str1, const void *str2, size_t n);
Copies n characters from str2 to str1. If str1 and str2 overlap the information is first completely read from str1 and then written to str2 so that the characters are copied correctly.
Returns the argument str1.
memset
Declaration:
void *memset(void *str, int c, size_t n);
Copies the character c (an unsigned char) to the first n characters of the string pointed to by the argument str.
The argument str is returned.
strcat
Declaration:
char *strcat(char *str1, const char *str2);
Appends the string pointed to by str2 to the end of the string pointed to by str1. The terminating null character of str1 is overwritten. Copying stops once the terminating null character of str2 is copied. If overlapping occurs, the result is undefined.
The argument str1 is returned.
strncat
Declaration:
char *strncat(char *str1, const char *str2, size_t n);
Appends the string pointed to by str2 to the end of the string pointed to by str1 up to n characters long. The terminating null character of str1 is overwritten. Copying stops once n characters are copied or the terminating null character of str2 is copied. A terminating null character is always appended to str1. If overlapping occurs, the result is undefined.
The argument str1 is returned.
strchr
Declaration:
char *strchr(const char *str, int c);
Searches for the first occurrence of the character c (an unsigned char) in the string pointed to by the argument str. The terminating null character is considered to be part of the string.
Returns a pointer pointing to the first matching character, or null if no match was found.
strcmp
Declaration:
int strcmp(const char *str1, const char *str2);
Compares the string pointed to by str1 to the string pointed to by str2.
Returns zero if str1 and str2 are equal. Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.
strncmp
Declaration:
int strncmp(const char *str1, const char *str2, size_t n);
Compares at most the first n bytes of str1 and str2. Stops comparing after the null character.
Returns zero if the first n bytes (or null terminated length) of str1 and str2 are equal. Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.
strcoll
Declaration:
int strcoll(const char *str1, const char *str2);
Compares string str1 to str2. The result is dependent on the LC_COLLATE setting of the location.
Returns zero if str1 and str2 are equal. Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.
strcpy
Declaration:
char *strcpy(char *str1, const char *str2);
Copies the string pointed to by str2 to str1. Copies up to and including the null character of str2. If str1 and str2 overlap the behavior is undefined.
Returns the argument str1.
strncpy
Declaration:
char *strncpy(char *str1, const char *str2, size_t n);
Copies up to n characters from the string pointed to by str2 to str1. Copying stops when n characters are copied or the terminating null character in str2 is reached. If the null character is reached, the null characters are continually copied to str1 until n characters have been copied.
Returns the argument str1.
strcspn
Declaration:
size_t strcspn(const char *str1, const char *str2);
Finds the first sequence of characters in the string str1 that does not contain any character specified in str2.
Returns the length of this first sequence of characters found that do not match with str2.
strerror
Declaration:
char *strerror(int errnum);
Searches an internal array for the error number errnum and returns a pointer to an error message string.
Returns a pointer to an error message string.
strlen
Declaration:
size_t strlen(const char *str);
Computes the length of the string str up to but not including the terminating null character.
Returns the number of characters in the string.
strpbrk
Declaration:
char *strpbrk(const char *str1, const char *str2);
Finds the first character in the string str1 that matches any character specified in str2.
A pointer to the location of this character is returned. A null pointer is returned if no character in str2 exists in str1.
strrchr
Declaration:
char *strrchr(const char *str, int c);
Searches for the last occurrence of the character c (an unsigned char) in the string pointed to by the argument str. The terminating null character is considered to be part of the string.
Returns a pointer pointing to the last matching character, or null if no match was found.
strspn
Declaration:
size_t strspn(const char *str1, const char *str2);
Finds the first sequence of characters in the string str1 that contains any character specified in str2.
Returns the length of this first sequence of characters found that match with str2.
strstr
Declaration:
char *strstr(const char *str1, const char *str2);
Finds the first occurrence of the entire string str2 (not including the terminating null character) which appears in the string str1.
Returns a pointer to the first occurrence of str2 in str1. If no match was found, then a null pointer is returned. If str2 points to a string of zero length, then the argument str1 is returned.
strtok
Declaration:
char *strtok(char *str1, const char *str2);
Breaks string str1 into a series of tokens. If str1 and str2 are not null, then the following search sequence begins. The first character in str1 that does not occur in str2 is found. If str1 consists entirely of characters specified in str2, then no tokens exist and a null pointer is returned. If this character is found, then this marks the beginning of the first token. It then begins searching for the next character after that which is contained in str2. If this character is not found, then the current token extends to the end of str1. If the character is found, then it is overwritten by a null character, which terminates the current token. The function then saves the following position internally and returns.
Subsequent calls with a null pointer for str1 will cause the previous position saved to be restored and begins searching from that point. Subsequent calls may use a different value for str2 each time.
strxfrm
Declaration:
size_t strxfrm(char *str1, const char *str2, size_t n);
Transforms the string str2 and places the result into str1. It copies at most n characters into str1 including the null terminating character. The transformation occurs such that strcmp applied to two separate converted strings returns the same value as strcoll applied to the same two strings. If overlapping occurs, the result is undefined.
Returns the length of the transformed string (not including the null character).
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