C++ list/vector problem

weiss

I'm trying to learn some C++ and a simple program i've written keeps crashing.. i can't see any bug in the code, but i'd like a second opinion on what the problem is.

it crashes on exit and after a little tracing in debugger, it looks like a null dereference pointer passed to a string copy function part of the call to free()

so it's a compiler problem or my code isn't written properly?

i'm using mingw g++ but it also crashes with intel compiler.

[PHP]
#include <algorithm>
#include <iostream>
#include <string>
#include <list>

using namespace std;

/*
mutate case of letters in a word and
store the results in a list of strings

example for "cat"

cat
Cat
cAt
CAt
caT
CaT
cAT
CAT
*/
void mutate_case(list<string>& wordlist, string word)
{
int *index = new int[word.length()];
int len;
string str;
int perms = 1;

for(size_t i(0);i < word.length();i++) {
str.push_back(tolower(word));
index = 0;
perms *= 2;
}

for(int i(0);i < perms;i++) {
wordlist.push_back(str);

if(++index[0] > 1) {
index[0] = 0;

for(len = 1;++index[len] > 1;len++)
index[len] = 0;

for(int j(1);j <= len;j++)
str[j] = (index[j] == 0) ? word[j] : toupper(word[j]);
}
str[0] = (index[0] == 0) ? word[0] : toupper(word[0]);
}

delete []index;
}

/*
create all permutations of a word

example for "cat"

act
atc
cat
cta
tac
tca
*/
void permutate(list<string>& wordlist, string word)
{
sort(word.begin(),word.end());

do {
wordlist.push_back(word);
} while(next_permutation(word.begin(),word.end()));
}
int main(int argc, char *argv[])
{
list<string> permutations;
list<string> wordlist;

if(argc != 2) {
cout << "\nUsage:perm <WORD>\n";
return(0);
}

mutate_case(wordlist,argv[1]);
permutate(permutations,argv[1]);

system("pause");
return(0);
}

[/PHP]

thanks in advance for any advice.

Señor Juárez

I might be totally off here, but shouldn't it be

delete index;

instead of

delete []index;

?

weiss

delete index;

instead of

delete []index;

no, i think the second way is "proper" way to remove dynamic array.
found problem in mutate_case()

[PHP]
for(len = 1;++index[len] > 1;len++)
index[len] = 0;
[/PHP]

there's no bounds checking so it overwrites memory outside array.
changed it to

[PHP]
for(len = 1;++index[len] > 1 && len < str.length();len++)
index[len] = 0;
[/PHP]

and also:

[php]int *index = new int[word.length()];[/php]

[php]int *index = new int[word.length() + 1];[/php]

which works..but the whole function needs to be written better.