A Little C Primer/C Standard Utility Library & Time Library

The utility functions library features a grab-bag of functions. It requires the declaration: #include <stdlib.h> Useful functions include: atof( <string> ) Convert numeric string to double value. atoi( <string> ) Convert numeric string to int value. atol( <string> ) Convert numeric string to long value. rand() Generates pseudorandom integer. srand( <seed> ) Seed random-number generator -- "seed" is an "int". exit( <status> ) Exits program -- "status" is an "int". system( <string> ) Tells system to execute program given by "string". abs( n ) Absolute value of "int" argument. labs( n ) Absolute value of long-int argument. The functions "atof()", "atoi()", and "atol()" will return 0 if they can't convert the string given them into a value. The time and date library includes a wide variety of functions, some of them obscure and nonstandard. This library requires the declaration: #include <time.h> The most essential function is "time()", which returns the number of seconds since midnight proleptic Coordinated Universal Time (UTC) of January 1, 1970, not counting leap seconds. It returns a value as "time_t" (a "long") as defined in the header file. The following function uses "time()" to implement a program delay with resolution in seconds: /* delay.c */ #include <stdio.h> #include <time.h> void sleep( time_t delay ); void main() { puts( "Delaying for 3 seconds." ); sleep( 3 ); puts( "Done!" ); } void sleep( time_t delay ) { time_t t0, t1; time( &t0 ); do { time( &t1 ); } while (( t1 - t0 ) < delay ); } The "ctime()" function converts the time value returned by "time()" into a time-and-date string. The following little program prints the current time and date: /* time.c */ #include <stdio.h> #include <time.h> void main() { time_t *t; time( t ); puts( ctime( t ) ); } This program prints a string of the form: Tue Dec 27 15:18:16 1994 Further reading C Programming/Standard libraries C Programming/C Reference C++ Programming/Code/Standard C Library