| Previous | Contents | Index |
Uses date and time information stored in a tm structure to create an output string. The format of the output string is controlled by a format string.
#include <time.h>Function Variants Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the strftime function that is equivalent to the behavior before OpenVMS Version 7.0.size_t strftime (char *s, size_t maxsize, const char *format, const struct tm *timeptr);
s
A pointer to the resultant string.maxsize
The maximum number of bytes to be stored in the resultant string, including the null terminator.format
A pointer to a string that controls the format of the output string.timeptr
A pointer to the local time ( tm ) structure. The tm structure is defined in the <time.h> header file.
The strftime function uses data in the structure pointed to by timeptr to create the string pointed to by s. A maximum of maxsize bytes is copied to s.The format string consists of zero or more conversion specifications and ordinary characters. All ordinary characters (including the terminating null character) are copied unchanged into the output string. A conversion specification defines how data in the tm structure is formatted in the output string.
A conversion specification consists of a percent (%) character followed by one or more optional characters (see Table REF-7), and concluding with a conversion specifier (see Table REF-8). If any of the optional characters listed in Table REF-7 are specified, they must appear in the order shown in the table.
The strftime function behaves as if it called tzset .
Table REF-7 Optional Elements of strftime Conversion Specifications Element Meaning -- Optional with the field width to specify that the field is left-justified and padded with spaces. This cannot be used with the 0 element. 0 Optional with the field width to specify that the field is right-justified and padded with zeros. This cannot be used with the -- element. field width A decimal integer that specifies the maximum field width .precision A decimal integer that specifies the precision of data in a field. For the d, H, I, j, m, M, o, S, U, w, W, y, and Y conversion specifiers, the precision specifier is the minimum number of digits to appear in the field. If the conversion specification has fewer digits than that specified by the precision, leading zeros are added.
For the a, A, b, B, c, D, E, h, n, N, p, r, t, T, x, X, Z, and % conversion specifiers, the precision specifier is the maximum number of characters to appear in the field. If the conversion specification has more characters than that specified by the the precision, characters are truncated on the right.
The default precision for the d, H, I, m, M, o, S, U, w, W, y and Y conversion specifiers is 2; the default precision for the j conversion specifier is 3.
Note that the list of conversion specifications in Table REF-7 are extensions to the XPG4 specification.
Table REF-8 lists the conversion specifiers. The strftime function uses fields in the LC_TIME category of the program's current locale to provide a value. For example, if %B is specified, the function accesses the mon field in LC_TIME to find the full month name for the month specified in the tm structure. The result of using invalid conversion specifiers is undefined.
Table REF-8 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 C The century number (the year divided by 100 and truncated to an integer) as a decimal number (00 -- 99) d The day of the month as a decimal number (01 -- 31) D Same as %m/%d/%y e The day of the month as a decimal number (1 -- 31) in a 2-digit field with the leading space character fill Ec The locale's alternative date and time representation EC The name of the base year (period) in the locale's alternative representation Ex The locale's alternative date representation EX The locale's alternative time representation Ey The offset from the base year ( %EC ) in the locale's alternative representation EY The locale's full alternative year representation h Same as %b 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) n The new-line character Od The day of the month using the locale's alternative numeric symbols Oe The date of the month using the locale's alternative numeric symbols OH The hour (24-hour clock) using the locale's alternative numeric symbols OI The hour (12-hour clock) using the locale's alternative numeric symbols Om The month using the locale's alternative numeric symbols OM The minutes using the locale's alternative numeric symbols OS The seconds using the locale's alternative numeric symbols Ou The weekday as a number in the locale's alternative representation (Monday=1) OU The week number of the year (Sunday as the first day of the week) using the locale's alternative numeric symbols OV The week number of the year (Monday as the first day of the week) as a decimal number (01 -- 53) using the locale's alternative numeric symbols. If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1. Ow The weekday as a number (Sunday=0) using the locale's alternative numeric symbols OW The week number of the year (Monday as the first day of the week) using the locale's alternative numeric symbols Oy The year without the century using the locale's alternative numeric symbols p The locale's equivalent of the AM/PM designations associated with a 12-hour clock r The time in AM/PM notation R The time in 24-hour notation ( %H:%M ) S The second as a decimal number (00 -- 61) t The tab character T The time ( %H:%M:%S ) u The weekday as a decimal number between 1 and 7 (Monday=1) U The week number of the year (the first Sunday as the first day of week 1) as a decimal number (00 -- 53) V The week number of the year (Monday as the first day of the week) as a decimal number (00 -- 53). If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1. 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 Time-zone name or abbreviation. If time-zone information is not available, no character is output. % Literal % character.
x The number of characters placed into the array pointed to by s, not including the terminating null character. 0 Indicates an error occurred. The contents of the array are indeterminate.
#include <stdlib.h> #include <stdio.h> #include <time.h> #include <locale.h> #include <errno.h> #define NUM_OF_DATES 7 #define BUF_SIZE 256 /* This program formats a number of different dates, once */ /* using the C locale and then using the fr_FR.ISO8859-1 */ /* locale. Date and time formatting is done using strftime(). */ main() { int count, i; char buffer[BUF_SIZE]; struct tm *tm_ptr; time_t time_list[NUM_OF_DATES] = {500, 68200000, 694223999, 694224000, 704900000, 705000000, 705900000}; /* Display dates using the C locale */ printf("\nUsing the C locale:\n\n"); setlocale(LC_ALL, "C"); for (i = 0; i < NUM_OF_DATES; i++) { /* Convert to a tm structure */ tm_ptr = localtime(&time_list[i]); /* Format the date and time */ count = strftime(buffer, BUF_SIZE, "Date: %A %d %B %Y%nTime: %T%n%n", tm_ptr); if (count == 0) { perror("strftime"); exit(EXIT_FAILURE); } /* Print the result */ printf(buffer); } /* Display dates using the fr_FR.ISO8859-1 locale */ printf("\nUsing the fr_FR.ISO8859-1 locale:\n\n"); setlocale(LC_ALL, "fr_FR.ISO8859-1"); for (i = 0; i < NUM_OF_DATES; i++) { /* Convert to a tm structure */ tm_ptr = localtime(&time_list[i]); /* Format the date and time */ count = strftime(buffer, BUF_SIZE, "Date: %A %d %B %Y%nTime: %T%n%n", tm_ptr); if (count == 0) { perror("strftime"); exit(EXIT_FAILURE); } /* Print the result */ printf(buffer); } }
Running the example program produces the following result:
Using the C locale: Date: Thursday 01 January 1970 Time: 00:08:20 Date: Tuesday 29 February 1972 Time: 08:26:40 Date: Tuesday 31 December 1991 Time: 23:59:59 Date: Wednesday 01 January 1992 Time: 00:00:00 Date: Sunday 03 May 1992 Time: 13:33:20 Date: Monday 04 May 1992 Time: 17:20:00 Date: Friday 15 May 1992 Time: 03:20:00 Using the fr_FR.ISO8859-1 locale: Date: jeudi 01 janvier 1970 Time: 00:08:20 Date: mardi 29 février 1972 Time: 08:26:40 Date: mardi 31 décembre 1991 Time: 23:59:59 Date: mercredi 01 janvier 1992 Time: 00:00:00 Date: dimanche 03 mai 1992 Time: 13:33:20 Date: lundi 04 mai 1992 Time: 17:20:00 Date: vendredi 15 mai 1992 Time: 03:20:00 |
Returns the length of a string of ASCII characters. The returned length does not include the terminating null character (\0).
#include <string.h>size_t strlen (const char *str);
str
A pointer to the character string.
x The length of the string.
Does a case-insensitive comparison between two 7-bit ASCII strings.
#include <strings.h>int strncasecmp (const char *s1, const char *s2, size_t n);
s1
The first of two strings to compare.s2
The second of two strings to compare.n
The maximum number of bytes in a string to compare.
The strncasecmp function is case-insensitive. The returned lexicographic difference reflects a conversion to lowercase. The strncasecmp function is similar to the strcasecmp function, but also compares size. If the size specified by n is read before a NULL, the comparison stops.The strcasecmp function works for 7-bit ASCII compares only. Do not use this function for internationalized applications.
n An integer value greater than, equal to, or less than 0 (zero), depending on whether s1 is greater than, equal to, or less than s2.
Appends not more than maxchar characters from str_2 to the end of str_1.
#include <string.h>Function Variants The strncat function has variants named _strncat32 and _strncat64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.10 for more information on using pointer-size-specific functions.char *strncat (char *str_1, const char *str_2, size_t maxchar);
str_1, str_2
Pointers to null-terminated character strings.maxchar
The number of characters to concatenate from str_2, unless strncat first encounters a null terminator in str_2. If maxchar is 0, no characters are copied from str_2.
A null character is always appended to the result of the strncat function. If strncat reaches the specified maximum, it sets the next byte in str_1 to the null character.
x The address of the first argument, str_1, which is assumed to be large enough to hold the concatenated result.
Compares not more than maxchar characters of two ASCII character strings and returns a negative, 0, or positive integer, indicating that the ASCII values of the individual characters in the first string are less than, equal to, or greater than the values in the second string.
#include <string.h>int strncmp (const char *str_1, const char *str_2, size_t maxchar);
str_1, str_2
Pointers to character strings.maxchar
The maximum number of characters (beginning with the first) to search in both str_1 and str_2. If maxchar is 0, no comparison is performed and 0 is returned (the strings are considered equal).
The strncmp function compares no more than maxchar characters from the string pointed to by str_1 to the string pointed to by str_2. The strings are compared until a null character is encountered, the strings differ, or maxchar is reached. Characters that follow a difference or a null character are not compared.
< 0 Indicates that str_1 is less than str_2. = 0 Indicates that str_1 equals str_2. > 0 Indicates that str_1 is greater than str_2.
| #1 |
|---|
#include <string.h>
#include <stdio.h>
main()
{
printf( "%d\n", strncmp("abcde", "abc", 3));
}
|
When linked and executed, this example returns 0, because the first 3 characters of the 2 strings are equal:
$ run tmp 0
| #2 |
|---|
#include <string.h>
#include <stdio.h>
main()
{
printf( "%d\n", strncmp("abcde", "abc", 4));
}
|
When linked and executed, this example returns a value greater than 0 because the first 4 characters of the 2 strings are not equal (The "d" in the first string is not equal to the null character in the second):
$ run tmp 100
Copies not more than maxchar characters from source into dest.
#include <string.h>Function Variants The strncpy function has variants named _strncpy32 and _strncpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.10 for more information on using pointer-size-specific functions.char *strncpy (char *dest, const char *source, size_t maxchar);
dest
Pointer to the destination character string.source
Pointer to the source character string.maxchar
The maximum number of characters to copy from source to dest up to but not including the null terminator of source.
The strncpy function copies no more than maxchar characters from source to dest, up to but not including the null terminator of source. If source contains less than maxchar characters, dest is padded with null characters. If source contains greater than or equal to maxchar characters, as many characters as possible are copied to dest. Be aware that the dest argument might not be terminated by a null character after a call to strncpy .
x The address of dest.
| Previous | Next | Contents | Index |