Unclear pointer and array Post: 302884150

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Top Forums Programming Unclear pointer and array Post 302884150 by yifangt on Friday 17th of January 2014 04:49:19 PM

01-17-2014

Registered User

Unclear pointer and array

Hello,
The purpose of the program is to print a sub string from the prompt inputs. I do not understand why char pointer does not work but char array will for line 40 and Line 41.

Code:

./a.out thisisatest 0 8
substring = "thisisat"

And my code is:

Code:

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

char *substring(size_t start, size_t stop, const char *src, char *dst,
        size_t size)
{
    unsigned int count = stop - start;
    if (count >= --size) {
    count = size;
    }
    sprintf(dst, "%.*s", count, src + start);
    return dst;
}

int main(int argc, char **argv)
{

    char *text; //Line 40, change to text[100] will work
    char *a;    //Line 41, change to a[100] will work
    int start, end;

    if (argc != 4) {
    printf("Error! Usage:\n\t \
argv[0]=program;\n\t \
argv[1]=input string\n\t \
argv[2]=start_position of string\n\t \
argv[3]=end_postion of string\n");

    return 1;
    }

    strcpy(text, argv[1]);
    start = atoi(argv[2]);
    end = atoi(argv[3]);

    printf("substring = \"%s\"\n",
       substring(start, end, text, a, sizeof(a)));

    return 0;
}

Thanks a lot!

Last edited by yifangt; 01-17-2014 at 05:50 PM.. Reason: adding tags

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LEARN ABOUT DEBIAN

colorreset

COLORS(3)						   libbash colors Library Manual						 COLORS(3)

NAME

     colors -- libbash library for setting tty colors.

SYNOPSIS

     colorSet	  <color>
     colorReset
     colorPrint   [<indent>] <color> <text>
     colorPrintN  [<indent>] <color> <text>

DESCRIPTION

   General
     colors is a collection of functions that make it very easy to put colored text on tty.

     The function list:
	   colorSet	    Sets the color of the prints to the tty to COLOR
	   colorReset	    Resets current tty color back to normal
	   colorPrint	    Prints TEXT in the color COLOR indented by INDENT (without adding a newline)
	   colorPrintN	    The same as colorPrint, but trailing newline is added

     Detailed interface description follows.

   Available colors:
	   Green
	   Red
	   Yellow
	   White
     The color parameter is non-case-sensitive (i.e. RED, red, ReD, and all the other forms are valid and are the same as Red).

FUNCTIONS DESCRIPTIONS

   colorSet <color>
     Sets the current printing color to color.

   colorReset
     Resets current tty color back to normal.

   colorPrint [<indent>] <color>
     Prints text using the color color indented by indent (without adding a newline).

     Parameters:

       <indent>
	 The column to move to before start printing.  This parameter is optional. If ommitted - start output from current cursor position.

       <color>
	 The color to use.

       <color>
	 The text to print.

   colorPrintN [<indent>] <color>
     The same as colorPrint, except a trailing newline is added.

EXAMPLES

     Printing a green 'Hello World' with a newline:

	  Using colorSet:
		  $ colorSet green
		  $ echo 'Hello World'
		  $ colorReset

	  Using colorPrint:
		  $ colorPrint 'Hello World'; echo

	  Using colorPrintN:
		  $ colorPrintN 'Hello World'

AUTHORS

     Hai Zaar <haizaar@haizaar.com>
     Gil Ran <gil@ran4.net>

SEE ALSO

     ldbash(1), libbash(1)

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