C++ read text file into an array

Question

I'm trying to read a text file containing 20 names into an array of strings, and then print each string to the screen.

string monsters[20];
ifstream inData;
inData.open("names.txt");
for (int i=0;i<monsters->size();i++){
    inData >> monsters[i];
    cout << monsters[i] << endl;
}inData.close();

However when I run this code the loop is executed but nothing is read into the array. Where have I gone wrong?

how are the 20 names in the file separated? newline, space or a custom delimiter? — Evert, May 01 '12 at 11:16
It does compile and the rest of the program runs fine. And sorry forgot to mention that, the names are separated by new lines. — pjmil, May 01 '12 at 11:18
I don't know a lot about C++ but I would ask you to put a breakpoint inside the loop anc check. I suspect the "monsters->size()" statement. — maths-help-seeker, May 01 '12 at 11:20

score 6 · Accepted Answer · edited May 02 '12 at 12:08

6

Your for loop terminating condition is wrong:

i < monsters->size()

This will actually call size() on the first string in your array, since that is located at the first index. (monsters is equivalent to monsters[0]) Since it's empty by default, it returns 0, and the loop will never even run.

Remember, C++ does not have a size() operator for arrays. You should instead use the constant 20 for your terminating condition.

i < 20

edited May 02 '12 at 12:08

Ashwin

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answered May 01 '12 at 11:20

penguinvasion

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And the constant 20 should be declared somewhere as `const uint8_t numberOfMonsters = 20;` – Vincenzo Pii May 01 '12 at 11:21
OK, I've applied this, but it still isn't reading anything from the file. Do I need to add something to iterate through each newline? – pjmil May 01 '12 at 11:32
@pjmil116, does the file definitely get opened? Are the reads succeeding? – hmjd May 01 '12 at 11:40
Ifstream's >> operator is separated by spaces by default. It will automatically iterate through "words". You can use getline(inData, monsters[i]) if you want to do it by line. But I can't see any other reason why this code isn't working. – penguinvasion May 01 '12 at 11:42
@hmjd I've applied all of the changes, it still only displays 20 blank lines in the cout though. – pjmil May 01 '12 at 11:51
Also, the file is saved as names.txt in the project's folder. – pjmil May 01 '12 at 11:54
Make sure your working directory is set to that project folder that names.txt is located in. You can use the is_open() function on inData to check whether there were any errors opening the file. – penguinvasion May 01 '12 at 11:58
1

@puller `uint8_t` is probably overkill here. `int` or `unsigned int` are perfectly fine if there is no additional requirement. – Quentin Pradet May 01 '12 at 17:29

score 3 · Answer 2 · answered May 01 '12 at 11:21

monsters->size() is 0 at runtime. Change that line to for (int i=0;i<20;i++).

 string monsters[20];
    ifstream inData;
    inData.open("names.txt");
    for (int i=0;i<20;i++){
        inData >> monsters[i];
        cout << monsters[i] << endl;
    }inData.close();

C++ read text file into an array

2 Answers2