Solved

Loading arrays from text file...again :P

Posted on 2003-10-29
7
277 Views
Last Modified: 2010-04-02
I asked a very similar qustion earlier here and got the answer I needed,
but now my program has changed and I'm running into some small problems.
I can load the values from the file into the 2d array perfectly, but when I try to
run an if to test the values i get screwed. This code should printf("%s", textures[0]); but
prints nothing.  the first value of map.txt is 9, i.e.
cat map.txt
9 0 0 1 1 3 3 4 5 6 7

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;

int main () {
  FILE * pFile;
  long lSize;
  char * buffer;

  pFile = fopen ("map.txt" , "rb" );
  if (pFile==NULL) exit (1);
  fseek (pFile , 0 , SEEK_END);
  lSize = ftell (pFile);
  rewind (pFile);
.
  buffer = (char*) malloc (lSize);
  if (buffer == NULL) exit (2);
  fread (buffer,1, lSize,pFile);

  char * pch;
  pch = strtok (buffer," ");

  int x = 0;
  int y = 0;

  char* matrix[15][20];

  while (pch != NULL)
  {
    if(y <= 19)
    {
      matrix[x][y] = pch;
      pch = strtok (NULL, " ,.");
      y++;
    }
    else
    {
     y = 0;
     x++;
    }
  }
/* ======================================================================*/
  char *textures[] = {".\\images\\stone.bmp", ".\\images\\woodtile.bmp"};
 
  for(int row = 0; row<15; row++){
    for(int col = 0; col<20; col++){
      if(matrix[0][0] == "9"){        //test matrix[0][0] to see if to equals "9"
        printf("%s", textures[0]);    //if it does then printf
      }
    }
  }
/* ======================================================================*/
  fclose (pFile);
  free (buffer);
  return 0;
}
0
Comment
Question by:w00t
  • 4
7 Comments
 

Author Comment

by:w00t
ID: 9647190
that period around line 19 shouldn't be there :P
0
 
LVL 8

Expert Comment

by:Exceter
ID: 9647260
>> char *textures[] = {".\\images\\stone.bmp", ".\\images\\woodtile.bmp"};
>>
>> ...
>> 
>> printf("%s", textures[0]);    //if it does then printf

textures is a char array. Its type is char*. textures[0] is a char, not a char*. You are attempting to display a string using the first char in the array as the pointer to the array. You could do this by saying,

printf("%s", &textures[0]);

but it is easiuer to simply say,

printf("%s", textures);

Exceter
0
 
LVL 8

Expert Comment

by:Exceter
ID: 9647348
Oops, strike that, I didn't notice that textures had multiple dimensions...
0
Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 
LVL 8

Expert Comment

by:Exceter
ID: 9647363
Here's the actual culprit, unless the sleepy seed demon is still haunting me,

>> char* matrix[15][20];

...

>>      if(matrix[0][0] == "9"){        //test matrix[0][0] to see if to equals "9"
>>        printf("%s", textures[0]);    //if it does then printf

matrix[0][0] is a char. "9" is a null terminated string containing the character 9 and a terminating null byte. Therefore its type is char*, not char. Replacing the double quotes with single quotes tells the compiler that this is a single character and not a string. Therefore, this should read,

if(matrix[0][0] == '9')
    printf("%s", textures[0]);

Cheers!
Exceter
0
 
LVL 8

Accepted Solution

by:
Exceter earned 100 total points
ID: 9647391
Grrr....

>> char* matrix[15][20];

Okay, I'm getting annoyed with myself now... This is an array of char* pointers and not chars...

>>      if(matrix[0][0] == "9"){        //test matrix[0][0] to see if to equals "9"
>>        printf("%s", textures[0]);    //if it does then printf

Understand that this comparison is still wrong, I simply stated the wrong reason for this. Both matrix[0][0] and "9" are char* pointers to a string. However, they can point to different arrays that contain the same data. Therefore, the pointer value of "9" is not equal to the pointer value for matrix[0][0] and the comparison fails. The actual data in the arrays is never compared. You need to use the strcmp function for this task, for example,

if( strcmp( matrix[0][0], "9" ) == 0 ) // If the data in the strings are equal, print textures[0]
   printf("%s", textures[0]);

I should have read your question more carefully from the beginning. My apologies.

Cheers!
Exceter
0
 
LVL 9

Expert Comment

by:tinchos
ID: 10546306
No comment has been added lately, so it's time to clean up this question.
I will leave the following recommendation for this question in the Cleanup topic area:

Accept: Exceter {http:#9647391}

Please leave any comments here within the next four days.
PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!

Tinchos
EE Cleanup Volunteer
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Written by John Humphreys C++ Threading and the POSIX Library This article will cover the basic information that you need to know in order to make use of the POSIX threading library available for C and C++ on UNIX and most Linux systems.   [s…
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

856 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question