Dividng a word into smaller segments

Question

I'm trying to implement a suffix tree.

int _tmain(int argc, _TCHAR* argv[])
{
    std::string text;
    cin >> text;
    int n = text.size();
    std::string first_array[sizeof(text) / sizeof(text[0])];

    for (int i = 0; i < text.size();i++)
    {
        first_array[i] = text.substr(i, n - i);
    }

    int T = sizeof(first_array) / sizeof(first_array[0]);
    sort(first_array, first_array + T);

    cout << endl << "The sorted tree:" << endl;
    for (int j = 0; j < sizeof(first_array) / sizeof(first_array[0]); j++)
        cout << j+1 << " | " << first_array[j] << endl;
}

That is my code. And for example, if the user inputs "hello", then the program should and I want it to show me this:

1 | ello
2 | hello
3 | llo
4 | lo
5 | o

But, it is showing me this instead (which is wrong and is NOT what I want):

1  |
2  |
3  |
4  |
5  |
6  |
7  |
8  |
9  |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
23 |
24 | ello
25 | hello
26 | llo
27 | lo
28 | o

Print the values of `sizeof(text) / sizeof(text[0])` for various inputs. (`sizeof` does not do what you think it does.) — molbdnilo, Feb 19 '15 at 10:39
cout << sizeof(text) / sizeof(text[0]) shows me the value "28". — deleteduser28283132112, Feb 19 '15 at 10:39
you use a std::string. Just use std::string::size() to get the text length — Vinz, Feb 19 '15 at 10:41
@suresegul So `first_array` is an array with 28 elements. That *could* be the problem. — molbdnilo, Feb 19 '15 at 10:52

emvee · Accepted Answer · 2015-02-19T11:23:02.760

1

sizeof(std::string) reports the size of the C++ string object (which is, apparently, 28 bytes large), which has nothing to do with the actual length of the string it contains. Use the ".size()" member function for the amount of characters contained in the string and sizing your array.

An alternative would be to use std::vector<std::string> and let it sort out the memory management:

std::vector<std::string> first_array;
for (int i = 0; i < text.size();i++)
         first_array.push_back( text.substr(i, n - i) );

For completeness' sake, here's a working program:

std::string text;
cout << "Please enter your text: ";
cin >> text;
std::vector<std::string> first_array;

for (int i = 0; i < text.size();i++)
    first_array.push_back( text.substr(i, n - i) );

sort(first_array.begin(), first_array.end());

cout << endl << "Suffix Tree (alphabetical order):" << endl;

std::vector<std::string>::iterator  ptr;
for(ptr=first_array.begin(); p!=first_array.end(); ptr++)
    cout << *ptr;
cout << endl;

edited Feb 19 '15 at 11:23

answered Feb 19 '15 at 10:55

emvee

4,371
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23

std::sort(first_array.begin(), first_array.end()) for in-place sort. See e.g. http://www.cplusplus.com/reference/algorithm/sort/ – emvee Feb 19 '15 at 11:07
Then you're declaring a C-style array of 20 std::string objects. – emvee Feb 19 '15 at 11:13
You don't. That's why you use "std::vector" and let the ".push_back()" allocate the elements for you. Then first_array.size() will tell you how many elements there are in the vector, after you're done appending all the suffixes. ["vector" is C++ speak for 'array', for all practical purposes] – emvee Feb 19 '15 at 11:19

Dividng a word into smaller segments

1 Answers1