Pure C function pointer on printing vowels twice Post: 302997580

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Top Forums Programming Pure C function pointer on printing vowels twice Post 302997580 by yifangt on Tuesday 16th of May 2017 11:30:58 PM

05-17-2017

Registered User

Pure C function pointer on printing vowels twice

Have difficulty to understand this pure C code to only print vowels twice from input string. Questions are commented at the end of each place.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
/*
 *Demonstrate the use of dispatch tables
 */

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

int putcharTwice(int c)
{
    if (putchar(c) == EOF || putchar(c) == EOF)  {//Q1
    return EOF;
    } else {
    return c;
    }
}

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

int main(int argc, char **argv)
{
/*This declares table as array of function pointers */
    int (*table[NUM_CHARS]) (int);   //Q2
    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;
}

The code was compiled without any problem,

Code:

$ echo "The quick brown fox jumps over the lazy dog!" | ./a.out
$ Thee quuiick broown foox juumps ooveer thee laazy doog!

Q1: How does the logic work by repeating the same condition on both sides of "||" ? I tried using only one side of the OR condition, the code compiled without error but did not work as expected.

Q2:Even not quite sure how to ask this question. Is this a prototype of a function? But the calling is without any parameter see Q3.

Q3: Calling of the function does not have a parameter at all. How does it work?

Q4: I thought I understand this line, but I must have wrong catch because of Q2.

Thanks a lot!

yifangt

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LEARN ABOUT OPENDARWIN

set_color

set_color(1)							       fish							      set_color(1)

NAME

       set_color - set_color - set the terminal color

set_color - set the terminal color
   Synopsis
       set_color [-v --version] [-h --help] [-b --background COLOR] [COLOR]

   Description
       Change the foreground and/or background color of the terminal. COLOR is one of black, red, green, brown, yellow, blue, magenta, purple,
       cyan, white and normal.

       o -b, --background Set the background color

       o -c, --print-colors Prints a list of all valid color names

       o -h, --help Display help message and exit

       o -o, --bold Set bold or extra bright mode

       o -u, --underline Set underlined mode

       o -v, --version Display version and exit

       Calling set_color normal will set the terminal color to whatever is the default color of the terminal.

       Some terminals use the --bold escape sequence to switch to a brighter color set. On such terminals, set_color white will result in a grey
       font color, while set_color --bold white will result in a white font color.

       Not all terminal emulators support all these features. This is not a bug in set_color but a missing feature in the terminal emulator.

       set_color uses the terminfo database to look up how to change terminal colors on whatever terminal is in use. Some systems have old and
       incomplete terminfo databases, and may lack color information for terminals that support it. Download and install the latest version of
       ncurses and recompile fish against it in order to fix this issue.

Version 1.23.1							  Sun Jan 8 2012						      set_color(1)

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