12570 - LAB12_Useful library functions   

Description

char * fgets ( char * str, int num, FILE * stream );


Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first.

A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.

A terminating null character is automatically appended after the characters copied to str.

/* fgets example */
#include <stdio.h>

int main()
{
   FILE * pFile;
   char mystring [100];

   pFile = fopen ("myfile.txt" , "r");
   if (pFile == NULL) perror ("Error opening file");
   else {
     if ( fgets (mystring , 100 , pFile) != NULL )
       puts (mystring);
     fclose (pFile);
   }
   return 0;
}

 

char * strtok ( char * str, const char * delimiters );

A sequence of calls to this function split str into tokens, which are sequences of contiguous characters separated by any of the characters that are part of delimiters.

On a first call, the function expects a C string as argument for str, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of the last token as the new starting location for scanning.

To determine the beginning and the end of a token, the function first scans from the starting location for the first character not contained in delimiters (which becomes the beginning of the token). And then scans starting from this beginning of the token for the first character contained in delimiters, which becomes the end of the token. The scan also stops if the terminating null character is found.

This end of the token is automatically replaced by a null-character, and the beginning of the token is returned by the function.

Once the terminating null character of str is found in a call to strtok, all subsequent calls to this function (with a null pointer as the first argument) return a null pointer.

The point where the last token was found is kept internally by the function to be used on the next call (particular library implementations are not required to avoid data races).

/* strtok example */
#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok (str," ,.-");
  while (pch != NULL)
  {
    printf ("%s\n",pch);
    pch = strtok (NULL, " ,.-");
  }
  return 0;
}

Input

Output

Sample Input  Download

Sample Output  Download

Tags




Discuss