递归算法中的分段错误

Question

I'm trying to write a recursive algorith which prints all posible combinations of a numbers character representives from a cellphone. Like the good old phones; 2: ABC, 3: DEF and so on.

Ex 23 should print AD, AE, AF, BD, BE, BF, CD, CE and CF. I've written the following algorithm, and I belive it should work. Though I don't know, because none of my compilers will let it finish.

#include <iostream>
#include <string>
#include <cstring>

using namespace std;
static int totalNbr = 0;


void coolKey(string number, string result)
{
   totalNbr++;
   string keychar[] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};


int nbrSize = number.length(); 


if (nbrSize == 0)   // Basecase - We've reached 0 didgets
{
     cout << result << endl;    
     return;
}

else
{

    for (int i = 0; i < keychar[(number[0]-'0')].length(); i++)
    {

        result += keychar[(number[0]-'0')][i]; // Append char to result.
        number = number.erase(0,1);            // Remove  first didget of the number (eg. "234" becomse "34")
        coolKey(number,result);                // Call coolKey with the new variables.
    }

}

}


int main()
{

    coolKey("23", "");
    return 0;
}

The output is:

ad                                                                                                                                                                                         
Segmentation fault                                                                                                                                                                         

I've tried searching for the error, and it seems to be some kind of stack overflow, or access to read only memory - but i can't seem to figure out where this happens. I first thought it was the deletion of string chars, but this didn't solve the problem.

I would be so thankfull if anybody could give me a hint here :-)

Best regards, Ben

Answer 1

You apparently try to erase the first digit ( number = number.erase(0,1); ) for each possible letter represented by the digit.

You should write that line before the for loop, not inside the loop. And even before that, store the digit being erased to be later used in the loop header.