6.087-10 C standard library: stdio.h, ctype.h, stdlib.h, assert.h,

OutlineReview Standard Library 1 6.087 Lecture 10 – January 25, 2010Review Standard Library 2 Review: Libraries• linking: binds symbols to addresses. • static linkage: occurs at compile time (static libraries). • dynamic linkage: occurs at run time (shared libraries). shared libraries: • ld.so -locates shared libraries • • ldconfig -updates links seen by ld.so • dlopen(),dlsym(),dlclose() -load shared libraries on demand. • compiling static libraries: gcc,ar • compiling shared libraries: gcc,ldconfig 2 Review: BTree• generalized search tree–multiple children. • except for root, each node can have between t and 2t children. • tree is always balanced. • Used in file systems, databases etc. 3 Review: Priority Queue• abstract data structure: many implementations • common implementations: heaps,bst,linked list • elements are queued and dequeued in order of priority. • operations: peek(),insert(),extract-max()/extract-min() 4 6.087 Lecture 10 – January 25, 2010Review Standard Library 5 : Opening, closing filesFILE∗ fopen(const char∗ filename,const char∗ mode) mode can be "r"(read),"w"(write),"a"(append). • "b" can be appended for binary input/output (unnecessary • in *nx)returns NULL on error.• FILE∗ freopen(const char∗ filename,const char∗ mode,FILE∗ stream) • redirects the stream to the file. • returns NULL on error. • Where can this be used? (redirecting stdin,stdout,stderr) int fflush (FILE∗ stream) flushes any unwritten data. • if stream is NULL flushes all outputs streams. • returns EOF on error. • 5 : File operationsint remove(const char∗ filename) removes the file from the file system. • retrn non-zero on error. • int rename(const char∗ oldname,const char∗ newname) renames file • returns non-zero on error (reasons?: permission, • existence) 6 :Temporary filesFILE∗ tmpfile(void) creates a temporary file with mode "wb+". • the file is removed automatically when program • terminates. char∗ tmpnam(char s[L_tmpnam]) creates a string that is not the name of an existing file. • return reference to internal static array if s is NULL. • Populate s otherwise.generates a new name every call.• 7 : Raw I/Osize_t fread(void∗ ptr,size_t size,size_t nobj,FILE∗ stream) reads at most nobj items of size size from stream into • ptr.returns the number of items read.• feof and ferror must be used to test end of file. • size_t fwrite (const void∗ ptr,size_t size,size_t nobj,FILE∗ stream) write at most nobj items of size size from ptr onto• stream.returns number of objects written.• 8 : File positionint fseek(FILE∗ stream, long offset,int origin ) sets file position in the stream. Subsequent read/write • begins at this locationorigin can be SEEK_SET, SEEK_CUR, SEEK_END.• returns non-zero on error. • long ftell (FILE∗ stream) returns the current position within the file. (limitation? long • data type).returns -1L on error.• int rewind(FILE∗ stream) sets the file pointer at the beginning. • equivalent to fseek(stream,0L,SEEK_SET);• 9 : File errorsvoid clearerr(FILE∗ stream) clears EOF and other error indicators on stream. • int feof(FILE∗ stream) • return non-zero (TRUE) if end of file indicator is set for stream. • only way to test end of file for functions such as fwrite(),fread() int ferror (FILE∗ stream) returns non-zero (TRUE) if any error indicator is set for • stream. 10 : Testing charactersisalnum(c) isalpha(c) || isdigit (c) iscntrl (c) control characters isdigit (c) 0-9 islower(c) ’a’-’z’ isprint (c) printable character (includes space) ispunct(c) punctuation isspace(c) space, tab or new line isupper(c) ’A’-’Z’ 11 : Memory functionsvoid∗ memcpy(void∗ dst,const void∗ src,size_t n) copies n bytes from src to location dst• returns a pointer to dst.• src and dst cannot overlap.• void∗ memmove(void∗ dst,const void∗ src,size_t n) behaves same as memcpy() function.• src and dst can overlap.• int memcmp(const void∗ cs,const void∗ ct,int n) compares first n bytes between cs and ct.• void∗ memset(void∗ dst,int c,int n) fills the first n bytes of dst with the value c.• returns a pointer to dst• 12 :Utilitydouble atof(const char∗ s) int atoi (const char∗ s) long atol(const char∗ s) converts character to float,integer and long respectively. • int rand() returns a pseduo-random numbers between 0 and • RAND_MAX void srand(unsigned int seed) sets the seed for the pseudo-random generator! • 13 : Exitingvoid abort(void) • causes the program to terminate abnormally. void exit (int status) • causes normal program termination. The value status is returned to the operating system. • 0 EXIT_SUCCESS indicates successful termination. Any other value indicates failure (EXIT_FAILURE) 14 :Exitingvoid atexit (void (∗fcn)(void)) • registers a function fcn to be called when the program terminates normally; • returns non zero when registration cannot be made. • After exit() is called, the functions are called in reverse order of registration. int system(const char∗ cmd) • executes the command in string cmd. • if cmd is not null, the program executes the command and returns exit status returned by the command. 15 :Searchign and sortingvoid bsearch ( const void key , const ∗∗void∗ base , size _t n, size _t size , int (∗cmp ) ( const void∗ keyval , const void∗ datum ) ); • searches base[0] through base[n-1] for *key. • function cmp() is used to perform comparison. • returns a pointer to the matching item if it exists and NULL otherwise. void qsort ( void∗ base,size _t n, size _t sz , int (∗cmp ) ( const void ∗ , const void ∗ ))! • sorts base[0] through base[n-1] inascending/descending order.• function cmp() is used to perform comparison. 16 :Diagnosticsvoid assert(int expression) used to check for invariants/code consistency during • debugging.does nothing when expression is true.• prints an error message indicating, expression, filename • and line number. Alternative ways to print filename and line number during execution is to use: __FILE__,__LINE__ macros. 17 :Variable argument listsVariable argument lists: functions can variable number of arguments. • the data type of the argument can be different for each • argument.atleast one mandatory argument is required.• Declaration: • int printf (char∗ fmt ,...); /∗fmt is last named argument∗/va_list ap ap defines an iterator that will point to the variable • argument.before using, it has to be initialized using va_start.• 18 :Variable argument listva_start( va_list ap, lastarg) ap lastarg refers to the name of the last named argument. • va_start is a macro. • va_arg(va_list ap, type) each call of va_arg points ap to the next argument. • type has to be inferred from the fixed argument (e.g. printf) • or determined based on previous argument(s). va_end(va_list ap) must be called before the function is exited. • 19 :Variable argument list(cont.)int sum( int num, . . . ) { va _list ap; int total =0; va _start (ap,num); while (num>0) { t o t a l +=va_arg ( ap , int ); num−−;}va_end(ap );return total ;} int suma=sum(4 ,1 ,2 ,3 ,4); /∗ called with five args ∗ /int sumb=sum(2 ,1 ,2); /∗ called with three args ∗ /20 time_t,clock_t, struct tm data types associated with time. struct tm:int tm_sec seconds int tm_min minutes int tm_hour hour since midnight (0,23) int tm_mday day of the month (1,31) int tm_mon month int tm_year years since 1900 int tm_wday day since sunday (0,6) int tm_yday day since Jan 1 (0,365) int tm_isdst DST flag 21 clock_t clock() returns processor time used since beginning of program. • divide by CLOCKS_PER_SEC to get time in seconds. • time_t time(time_t ∗ tp) returns current time (seconds since Jan 1 1970). • if tp is not NULL, also populates tp. • double difftime(time_t t1,time_t t2) returns difference in seconds. • time_t mktime(struct tm∗ tp) converts the structure to a time_t object.• returns -1 if conversion is not possible. • 22 char∗ asctime(const struct tm∗ tp) returns string representation of the form "Sun Jan 3 • 15:14:13 1988".returns static reference (can be overwritten by other calls).• struct tm∗ localtime(const time_t ∗ tp) converts calendar time to local time". • char∗ ctime(const time_t ∗ tp) converts calendar time to string representation of local • time".equivalent to sctime(locltime(tp))!• 23 size_t strftime (char∗ s,size_t smax,const char∗ fmt,const struct tm∗ tp) returns time in the desired format. • • does not write more than smax characters into the string s. %a abbreviated weekday name %A full weekday name %b abbreviated month name %B full month name %d day of the month %H hour (0-23) %I hour (0-12) %m month %M minute %p AM/PM %S second 24 MIT OpenCourseWarehttp://ocw.mit.edu 6.087 Practical Programming in CJanuary (IAP) 2010For information about citing these materials or our Terms of Use,visit: http://ocw.mit.edu/terms.