尋隱者不遇

尋隱者不遇 松下問童子，言師採藥去。只在此山中，雲深不知處。 ~賈島

C Time Library <ctime> • Types • clock_t-Clock type • size_t- Unsigned integral type • time_t - Time type • struct tm - Time structure (See Chapter 7) • Time manipulation • clock - Ticks since the program was launched • time - Get current time • mktime - Convert tm structure to time_t • Macro • CLOCKS_PER_SEC - Clock ticks per second • Conversion • asctime - Convert tm structure to string • ctime - Convert time_t value to string • gmtime- Convert time_t to tm as UTC time • localtime - Convert time_t to tm as local time • strftime - Format time as string

#include <ctime> time_t time ( time_t * timer ); time() /* time example */ #include <iostream> #include <ctime> int main () { time_t seconds; seconds = time(NULL); std::cout << seconds/3600 << " hours since" << " January 1, 1970\n"; return 0; } /* time example */ #include <iostream> #include <ctime> int main () { time_t seconds; time(&seconds); std::cout << seconds/3600 << " hours since" << " January 1, 1970\n"; return 0; }

#include <ctime> char * ctime ( const time_t * timer ); ctime() • Converts the time_t object (seconds since 1970.1.1) to a C string containing a human-readable version of the corresponding local time and date. /* ctime example */ #include <iostream> #include <ctime> int main () { time_t rawtime; time ( &rawtime ); std::cout << "The current local time is: " << ctime (&rawtime) << std::endl; return 0; } The current local time is: Sat Nov 10 11:57:33 2012 output

String Manipulation

<assert.h> <ctype.h> <errno.h> <float.h> <iso646.h> <limits.h> <locale.h> <math.h> <setjmp.h> <signal.h> <stdarg.h> <stddef.h> <stdio.h> <stdlib.h> <string.h> <time.h> <wchar.h> <wctype.h> Standard Header Q: What’s the difference between <cstring> and <string.h>?A: In C++, we include <cstring>; in C, we include <string.h>. Actually, including the standard header <cstring>will effectively include the standard C library header <string.h> within the std namespace.

strlen() #include <cstring> size_t strlen( char *str ); • Find length of string. #include <iostream> #include <cstring> using std::cout; using std::endl; int main() { char str[10]="Hello"; cout << sizeof str; cout << strlen(str); } 10 5 output

strchr() #include <cstring> char *strchr( const char *str, int ch ); • Find first occurrence of specified character in string. char str1[]="Hello"; char* r= strchr(str1, 108); cout << r << endl; llo output

strstr() #include <cstring> char *strstr( const char *str1, const char *str2 ); • Find first occurrence of specified string in another string. char str1[]="Hello Hello"; char str2[]="el"; char* r= strstr(str1, str2); cout << r << endl; ello Hello output

strcmp() #include <cstring> int strcmp( const char *str1, const char *str2 ); • Compare two strings. • char str1[] = "Hello"; • char str2[] = "Hello"; • int r= strcmp(str1, str2); • cout << r << endl; 0 output char str1[] = "Hello"; char str2[] = "He"; int r= strcmp(str1, str2); cout << r << endl; 1 output a positive number char str1[] = "Hello"; char str2[] = "Hello!!"; int r= strcmp(str1, str2); cout << r << endl; -1 output a negative number

strcpy() #include <cstring> char *strcpy(char *str1, const char *str2); • Copy str2 to str1, including its terminating null character. char str1[] = "Hello"; char str2[] = "abc"; strcpy(str1, str2); cout << str1 << endl; abc output

#include <cstring> char *strncpy( char *str1, const char *str2, size_t n); strncpy() • Copy at most n characters of str2 to str1, notincluding its terminating null character. char str1[] = "Hello"; char str2[] = "abc"; strncpy(str1, str2,2); cout << str1 << endl; abllo output

strcat() #include <cstring> char *strcat( char *str1, const char *str2 ); • Append one string to another. char str1[10] = "Hello"; char str2[] = "!!"; strcat(str1, str2); cout << str1 << endl; Hello!! output

Reference • Standard C Library • http://www.mers.byu.edu/docs/standardC/index.html • http://www.elook.org/programming/c/ • MSDN – String Manipulation

Exercise • Design a function int lower_string(char* str) to convert every lowercase letters in a string to uppercase. For example, • char str[] = "WoW"; • lower_string(str); • cout << str << endl; • The result will be "wow" • You may also utilize the tolower() function defined in C library ctype.

Exercise • Write a function int find(char* text, char* pattern), which can count the occurrence of pattern in text. For example, • find("This is an island.", "is") == 3 • find("Hello", "g") == 0 • Test your function with this main program. • Hint: You may utilize the strstr() function, or define a new function by yourself.

尋隱者不遇

尋隱者不遇

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