Pure C function pointer on printing vowels twice Post: 302997654

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Top Forums Programming Pure C function pointer on printing vowels twice Post 302997654 by yifangt on Wednesday 17th of May 2017 04:54:17 PM

05-17-2017

Registered User

Thanks Don and corona688!
I think my problem is my mis-understanding of the function putchar(c) so that I re-wrote it with putc() which helped me understand it.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>

/*Print a char twice like putchar, return char if successful, or EOF on error.*/

int putcharTwice(int c)
{
    if (putc(c, stdout) == EOF || putc(c, stdout) == EOF)  {//Q1
    return EOF;
    } else {
    return 0;        //NOT return c;
    }
}

#define NUM_CHARS (UCHAR_MAX + 1)    //UCHAR_MAX is in limits.h

  int (*table[NUM_CHARS]) (int);   //Q2, So moved outside main() to see this function pointer

int main(int argc, char **argv)
{
/*This declares table as array of function pointers */
    int i;
    int c;

    for (i = 0; i < UCHAR_MAX; i++) {
    // default is to call putchar 
    table[i] = putchar;
    }

    // but lower-case vowels show up twice 
    table['a'] = putcharTwice; //Q3, and following 4 lines
    table['e'] = putcharTwice; //Q3
    table['i'] = putcharTwice; //Q3
    table['o'] = putcharTwice; //Q3
    table['u'] = putcharTwice; //Q3

    while ((c = getchar()) != EOF) {
    table[c] (c); //Q4,
    }
    return 0;
}

Thanks a lot again!

yifangt

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LEARN ABOUT NETBSD

fputc

PUTC(3) 						   BSD Library Functions Manual 						   PUTC(3)

NAME

     fputc, putc, putchar, putc_unlocked, putchar_unlocked, putw -- output a character or word to a stream

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdio.h>

     int
     fputc(int c, FILE *stream);

     int
     putc(int c, FILE *stream);

     int
     putchar(int c);

     int
     putc_unlocked(int c, FILE *stream);

     int
     putchar_unlocked(int c);

     int
     putw(int w, FILE *stream);

DESCRIPTION

     The fputc() function writes the character c (converted to an ``unsigned char'') to the output stream pointed to by stream.

     putc() acts essentially identically to fputc(), but is a macro that expands in-line.  It may evaluate stream more than once, so arguments
     given to putc() should not be expressions with potential side effects.

     putchar() is identical to putc() with an output stream of stdout.

     The putc_unlocked() and putchar_unlocked() functions provide functionality identical to that of putc() and putchar(), respectively, but do
     not perform implicit locking of the streams they operate on.  In multi-threaded programs they may be used only within a scope in which the
     stream has been successfully locked by the calling thread using either flockfile(3) or ftrylockfile(3), and may later be released using
     funlockfile(3).

     The putw() function writes the specified int to the named output stream.

RETURN VALUES

     The functions, fputc(), putc() and putchar() return the character written.  If an error occurs, the value EOF is returned.  The putw() func-
     tion returns 0 on success; EOF is returned if a write error occurs, or if an attempt is made to write a read-only stream.

SEE ALSO

     ferror(3), fopen(3), getc(3), stdio(3)

STANDARDS

     The functions fputc(), putc(), and putchar(), conform to ANSI X3.159-1989 (``ANSI C89'').	The functions putc_unlocked() and
     putchar_unlocked() conform to ISO/IEC 9945-1:1996 (``POSIX.1'').

HISTORY

     The functions putc(), putchar(), and putw() first appeared in Version 6 AT&T UNIX.  The function fputc() appeared in Version 7 AT&T UNIX.

BUGS

     The size and byte order of an int varies from one machine to another, and putw() is not recommended for portable applications.

BSD
								    May 6, 2010 							       BSD

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