CODEWITHSUNDEEP
c++
Jim
Jim

Reputation: 101

C++ char/string reading problem

Again, I'm trying to make a simple program. It will read some kind of board, at the size of RxC. Each items on the board are letters, separated with spaces. This is a sample board:

A B C
D E F
G H I

After that, it will read an integer N, and for next N lines, read a string and process them one by one based on the given board. But now, I'm facing a problem with how to read them. Here is the code : 

#include<iostream>
using namespace std;

int r,c,el; char **arr;

int main()
{
    char *tes;
    int n;

    //start reading the puzzle
    cin >> r >> c; el=r;
    cout << el << endl;
    arr = new char * [3*(r+c)-6];
    for(int i=0;i<r;i++)
    {
        arr[i] = new char[c+1];
        for(int j=0;j<c;j++) cin >> arr[i][j];
        arr[i][c] = '\0';
    }
    for(int i=0;i<el;i++) cout << arr[i] << endl;

    cin >> n;
    while(n>0)
    {
        n--;
        cin >> tes;
        cout << tes << endl;
    }
}

I don't know what's wrong with this, it's seems OK to me. However, it always get runtime errors. I'm using latest MinGW and gdb debugger. On gdb I saw something like

"received signal SIGSEGV. Segmentation fault"

, and an 0xC0000005 error. I really have no idea what's going on here. I've tried both iostream(cin&cout) and cstdio(scanf,puts,etc.)

P.S.: I declare the variables globally, because I will process them on a different function out of the main() function. I set the size of the "height" of the array to (3*(r+c)-6), not to the normal (r) is because I will use the same array to store another strings later.

Upvotes: 0

Views: 682

Answers (4)

Kerrek SB
Kerrek SB

Reputation: 476930

Further to unwind's answer, your array has size 3*(r+c)-6, but you are looping over values i = 0; i < r;, which depending on the values may just run out of bounds (plus it makes no sense).

Upvotes: 0

Dan
Dan

Reputation: 13373

Segmentation fault usually means you are trying to access memory which hasn't been allocated, for instance

char* mystr = (char*)malloc(3*sizeof(char));
mystr[4] = 0.0;

will (most likely) cause a seg fault because you're accessing memory which you didn't allocate (mystr goes from 0 - 2).

Are you sure you're allocating the memory correctly? I'm not sure why you have 3*(r+c)-6.

Upvotes: 2

Paul R
Paul R

Reputation: 212929

In addition to the problems already noted by others, you haven't allocated any memory for tes - it's just a dangling pointer.

Change:

char *tes;

to, e.g.:

char tes[80];

Upvotes: 3

unwind
unwind

Reputation: 399703

A board of size R*C needs, not very surprisingly, r*c chars of storage. I fail to understand why you're allocating the board in so many steps. A single char* board = new char[r * c]; should do it, then just keep track of where in the array your're reading.

Upvotes: 3

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