Control

• errno - an external int which holds error numbers for the most recent error. Declared as extern int errno; in errno.h, and accessed by most error functions.
• perror - prints an error message
  • void perror(char s1[])
  • Prints s1 and an implementation defined error message out to stderr.
  • The error message is that indicated by the current value of errno, and may be accessed directly by char *strerror(int error_number)
• OpenFileError.c - Program that tests for the readability of a file

• The assert.h file provides a function void assert(int expression).
• If expression is 0, an error message of the form

  Assertion failed: expression, file <filename>, line <line> 

  is output to stderr, and execution is aborted.
• If NDEBUG is defined at the time <assert.h> is included, the assert macros are ignored.
• AssertNonZero.c - Program that asserts a divisor is non-zero

• This provides a facility to exit from deeply nested function calls.
• The declarations are in setjmp.h.
• int setjmp(jmp_buf environment) stores the current state information in environment, and returns 0.
• void longjmp(jmp_buf environment,int value) returns again from the setjmp that created the environment, returning the value specified.
• The function containing the setjmp must not have terminated.
• Some variables retain their values between the setjmp and return with longjmp.
• LongJump.c - Program that escapes from recursion using longjmp

• The time.h header declares several functions for manipulating the time and date.
• time_t time(time_t *tloc) - Returns the time since 00:00:00 GMT, Jan. 1, 1970, measured in seconds. If tloc is not NULL, the return value is also stored in the location to which tloc points.
• struct tm *localtime_r(const time_t *clock, struct tm *res); - Converts an elapsed time since epoch to a struct tm:

  struct  tm {
       int   tm_sec;    /* seconds after the minute - [0, 61], 61 for leap seconds */
       int   tm_min;    /* minutes after the hour - [0, 59] */
       int   tm_hour;   /* hour since midnight - [0, 23] */
       int   tm_mday;   /* day of the month - [1, 31] */
       int   tm_mon;    /* months since January - [0, 11] */
       int   tm_year;   /* years since 1900 */
       int   tm_wday;   /* days since Sunday - [0, 6] */
       int   tm_yday;   /* days since January 1 - [0, 365] */
       int   tm_isdst;  /* flag for alternate daylight savings time */
  };
  

• char *asctime_r(const struct tm *tm, char *buf, int buflen); - Converts a struct tm to a readable string.
• char *ctime(time_t *clock) - Converts the time pointed to by clock, representing the time in seconds since the Epoch (00:00:00 UTC, January 1, 1970), to local time in the form of a 25 character string.
• MyDate.c - Program that prints the date
• clock_t clock(void); - Returns the amount of CPU time (in clock ticks, often microseconds) used since the start of the calling process. Use CLOCKS_PER_SEC to convert to seconds.
• TimeFib.c - Program that times recursive Fibonacci

• unsigned int sleep(unsigned int seconds); - Suspends the calling process for seconds.
• void exit(int status); - Closes files, etc, and returns status to the OS.
• int atexit(void (*func)(void)); - Registers func as a function to be called at the start of exit processing.
• Exit.c - Program that sleeps, and exits with an exit function

int i1,i2;

scanf("%d %d",&i1,&i2);
printf("%d\n:,i1/i2); 

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void Byeee(void) {

    time_t elapsedSinceEpoch;

    time(&elapsedSinceEpoch);
    printf("My time is %s\n",ctime(&elapsedSinceEpoch));
}

int main(void) {

    FILE *File;

    atexit(Byeee);

    if ((File = fopen("/bin/ls","w")) == NULL) {
        perror("Opening system file");
        exit(-1);
    }
    fclose(File);
    return(0);
}