vector of characters
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Thread: vector of characters

  1. #1
    Join Date
    Dec 2009
    Posts
    58

    vector of characters

    Dear all,
    I am a newbie in C++ and having some difficulty storing value in a vector of characters. I am getting error "subscript out of range". Can a kind soul help me understand how to store the values 'id' in the vector 'AA' and access/output it.

    I have declared
    Code:
    int Nlinks, i;
    char  id[31];
    
    std::vector<int> AA; //Create an empty vector of type int ********** 
    
    for (i = 1; i <= Nlinks; i++)
        {
            ENgetlinkid(i,id);
            AA.push_back (id[31]);
        }
    for (i = 0; i < (char)AA.size(); i++)
        {
            cout << AA[i] << endl;
        }

  2. #2
    Join Date
    Apr 1999
    Posts
    27,423

    Re: vector of characters

    Quote Originally Posted by RePrasad View Post
    Dear all,
    I am a newbie in C++ and having some difficulty storing value in a vector of characters. I am getting error "subscript out of range".
    What is wrong with this program?
    Code:
    #include <iostream>
    int main()
    {
      char id[31];
      std::cout << id[31];
    }
    Hint: arrays are accessed starting at index 0 up to n-1, where n is the number of elements. The id array has 31 elements, but how is it being used in the cout statement?

    That is the same error you have in your program.

    Regards,

    Paul McKenzie

  3. #3
    Join Date
    Jan 2010
    Posts
    3

    Re: vector of characters

    Hi Paul,

    First of all I whould describe you what I understood from the function you have coded. I suppose you wanted to read out a link id belonging to a number 1-Nlinks.

    It's not clear why have you declared a vector of integer and get back in the function type of character and pushed into the vector of integer.

    It's also not clear how many ids you expect to receive from ENgetlinkid. Supposed you need a single integer only I would modify your code the following way.

    void ENgetlinkid(int i,int& id); // declared elsewhere

    int Nlinks=50, i;
    int id;
    std::vector<int> AA; //Create an empty vector of type int **********

    for (i = 1; i <= Nlinks; i++)
    {
    ENgetlinkid(i,id);
    AA.push_back(id);
    }
    for (vector<int>::iterator it = vector<int>::begin(); it != vector<int>::end() ;++it)
    {
    cout << *it << endl;
    }

    You got an exception because the upper bound of index in char id[31]; is 30.

    Best regards.

    Janos

  4. #4
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Hi Janos,
    The standard format in the software I am using for the coding to get the linkid is
    Code:
     DLLEXPORT int _stdcall  ENgetlinkid(int, char *);
    Here, I cannot use
    Code:
     int id
    This is why I have to use
    Code:
     char[31];
    An id with character and numbers (example, Pipe110)
    please guide me on how can I fix this one.

    Regards,
    RePrasad

  5. #5
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    The one I mentioned is from the header file (epanet2.h) of the software EPANET
    Code:
    DLLEXPORT int _stdcall  ENgetlinkid(int, char *);
    Just an additional clarification.

    Regards,
    RePrasad

  6. #6
    Join Date
    Apr 1999
    Posts
    27,423

    Re: vector of characters

    Quote Originally Posted by RePrasad View Post
    Here, I cannot use
    Code:
     int id
    This is why I have to use
    Code:
     char[31];
    Did you understand my post?
    Code:
    char x[31];  // an array declaration
    //...
    // The valid indexes of x are x[0], x[1], x[2], ... x[30].
    // There is no such element as x[31].
    If you don't understand how to properly access arrays, I suggest you go back and study the basics on arrays. Again, if an array has n elements, arrays are accessed starting at 0 and going to n-1, not n.

    Regards,

    Paul McKenzie

  7. #7
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Thanks a lot Paul. Pl. have patience. Sometimes there are simple mistakes which wont get caught easily

  8. #8
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Thank you very much for the quick response sir. I think I am trying to do exactly as you thought. I tried changing the storage from

    Code:
    AA.push_back (id[31]);
    to

    Code:
    AA.push_back(id[i]);
    and the cout line of the code accordingly. However I have a condition to add

    Code:
    if  
            ( fromnode == Nr || tonode == Nr)
            AA.push_back(id[i])

    and then cout
    Also, I have changed the vector type to char i.e.

    Code:
    vector<char> AA;

    I am getting weird characters

    Code:
    |[
    as output on console on 11 lines. Could you please help me identify and help me understand my mistake.

    Regards,
    RePrasad

  9. #9
    John E is offline Elite Member Power Poster
    Join Date
    Apr 2001
    Location
    Manchester, England
    Posts
    4,235

    Re: vector of characters

    So your code now looks like this...?

    Code:
    int Nlinks, i;
    char  id[31];
    
    std::vector<int> AA; //Create an empty vector of type int ********** 
    
    for (i = 1; i <= Nlinks; i++)
        {
            ENgetlinkid(i,id);
            AA.push_back (id[i]);
        }
    Nlinks is just some totally arbitrary number. If it's anything higher than 30 you will (again) be accessing elements that are off the end of the array (i.e. off the end of id[]).

    Apart from that, id[] has never been initialised anywhere so it will be a random chunk of memory filled with completely arbitrary data. That's why you're seeing weird characters. Don't assume that your computer knows what you know. If you want it to do something sensible, you need to give it every relevant instruction. You can't miss some of them out and assume it will know what you intended.
    "A problem well stated is a problem half solved. - Charles F. Kettering

  10. #10
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    The vector is a vector of characters instead of vector of integers

    Code:
    int Nlinks, i;
    char  id[31];
    
    std::vector<char> AA; //Create an empty vector of type char ********** 
    
    for (i = 1; i <= Nlinks; i++)
        {
            ENgetlinkid(i,id);
            AA.push_back (id[i]);
        }
    I am extremely sorry but could you please help me understand how to initialize the id[]
    Code:
    ENgetlinkid(i,id);
    would get the id of the link from the network within the loop 1 thru Nlinks (Nlinks is number of links which is obtained earlier)

  11. #11
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Thank you very much,
    I was able to initialize the vector. But now it prints blank (shows nothing) Please recommend a quick fix on this one.

  12. #12
    John E is offline Elite Member Power Poster
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    Apr 2001
    Location
    Manchester, England
    Posts
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    Re: vector of characters

    Quote Originally Posted by RePrasad View Post
    I am extremely sorry but could you please help me understand how to initialize the id[]
    Code:
    ENgetlinkid(i,id);
    would get the id of the link from the network within the loop 1 thru Nlinks (Nlinks is number of links which is obtained earlier)
    Okay, in which case you've left out the most important code which is probably heppening in ENgetlinkid(). Also, do you check anywhere that Nlinks can never be more than 30?

    Regarding the blank spaces, nobody can tell you why that's happening because you haven't shown enough code for anyone to be able to tell what's supposed to happen. It looks as if ENgetlinkid() gets an id of some sort - but only one character of that id ever gets pushed back to your vector. Is that what you intend to happen? I strongly suspect that you probably need a multi-dimensional array for id[], rather than the single dimension array that you specified. Or maybe you wanted a vector of strings, rather than a vector of single characters. Maybe you should be using AA.push_back (id); to some other kind of vector. It's impossible to guess because your intentions just aren't clear from the code you've provided.

    The bottom line is that if another programmer can't work out what you intended, the computer's got no chance!
    Last edited by John E; February 10th, 2010 at 12:54 AM.
    "A problem well stated is a problem half solved. - Charles F. Kettering

  13. #13
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Hello John,
    Thank you very much for your step-by-step advise.

    Here is the detailed code. What I intend to do is to read a network file and get its linkid "id" for a particular condition where either the starting or ending nodes are equal to root node.

    However, after going thru the code it is printing either weird characters or blank. I completely understand that I should have provided the complete code to you.

    MY INTEREST HERE IS TO STORE THE LINKS FOR THE CONDITION IN A VECTOR CALLED AA AND THEN ACCESS IT. SINCE I AM LEARNING THIS I AM TAKING MORE TIME THAN NORMAL.

    Regards,
    RePrasad

    HERE IS THE CODE FOR YOUR QUICK REFERENCE
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include<conio.h>
    #include "epanet2.h"
    #include <iostream>
    #include <cstdlib>
    #include <ctime>
    #include <vector> 
    #include <cmath>
    #include <fstream>
    #include <string>
    
    using namespace std;
    int main(int argc, char *argv[])
     {
    	fstream SaveFile("C:/tmp/Results.txt");
    	if ( !SaveFile )
    	{
    		cerr << "ERROR: could not open file '" << SaveFile << endl;
    		throw (-1);
    	}
    	char  input1[] = "Net1.inp";
    	char  input2[] = "NewNet1.inp";
        char  output2[] = "NewNet1.rpt";
    
        int   Nlinks;
        long  i;
        long  t;
        long  tstep;
        int   fromnode, tonode;
        char  id[31];
        int Nr;
    	
    
    	std::vector<char> AA; 
    
    	ENopen(input1);
    	ENgetcount(EN_LINKCOUNT, &Nlinks);
    
    	
    	printf("\nEnter the root node:Nr  ");
    	cin >> Nr;
    
    	for (i = 1; i <= Nlinks; i++)
    	{
    	
    	ENgetlinkid(i,id);
    	ENgetlinknodes(i,&fromnode,&tonode);
    		if  
    		( fromnode == Nr || tonode == Nr) 
    		SaveFile << id << endl;
    		AA.push_back (id[i]);
    	}
    		for (i = 0; i < (int)AA.size(); i++)
        		{
    		cout << AA[i] << endl;
       		}
    	
    	ENcloseQ();
        	ENreport();
        	ENclose();
    	SaveFile.close();
    
        return 0;
    }

  14. #14
    Join Date
    Aug 2000
    Location
    West Virginia
    Posts
    7,564

    Re: vector of characters

    The main problem is we do not know what ENgetlinkid(i,id) does.
    Assuming the id is returned via a strcpy, Is a char [31] big enough ?

    My guess is that John's suggest of using a vector<string> is what you want.

    relevant lines that change:

    Code:
    std::vector<std::string> AA; 
    
    //
    AA.push_back (id);

  15. #15
    Join Date
    Dec 2009
    Posts
    58

    Re: vector of characters

    Thank you very much for the analysis Phillip and Paul. Just to bring to your attention. The line corresponding the ENgetlinkid from the
    Code:
    epanet.h
    file is given below which I cannot make any changes to.

    Code:
    DLLEXPORT int _stdcall  ENgetlinkid(int, char *);
    Also given below is a standard format of retrieving id is given just for your reference from the toolkit help. It does not accept vector of string

    Code:
    ENgetlinkid
    int ENgetlinkid( int index, char* id )
    Description: Retrieves the ID label of a link with a specified index.
    Arguments:
    index: link index
    id: ID label of link
    Returns: Returns an error code.
    Notes:
    The ID label string should be sized to hold at least 15 characters.
    Link indexes are consecutive integers starting from 1.

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