adding string objects to an array via loop

Question

What i'm trying to do is create a template array class that will store values of a data type into an array. I have it working fine with int values, however working with string objects things start to break down.

I've taken out the block of code and tried it on it's own and I do get the same error. I'm sure I've learnt this, and I'm almost positive that the answer is something simple, trying to wrap my head around the pace in which we're learning c++ is a little crazy at times!

My best guess right now, is that I would need to tokenize the string and look for spaces. I tend to over think things though which lead to more confusion - thus me seeking out a answer here!

The code:

// Test String: Hello World this is a String Object
int stringSize = 7;
int count = 0;

string s[stringSize];

cout << "\nEnter " << stringSize << " one-word string values:\n";

while (count < stringSize) {

    string tmpVal;

    cin >> tmpVal;
    s[count] = tmpVal;

    count ++;
}

Answer 1

string s[stringSize]; is illegal because stringSize is not a constant. You must either use dynamic memory (i.e. string* s = new string [stringSize];), include stringsize as a template argument (don't do this, it doesn't actually solve the problem), use a fixed size value, or use an existing structure (I'd suggest vector, as in Bill's answer). The code below works fine on my compiler:

int main(int argc, char *argv[]) {
int stringSize = 7;
int count = 0;
string* s = new string [stringSize];
cout << "\nEnter " << stringSize << " one-word string values:\n";
while (count < stringSize) {
    string tmpVal;
    cin >> tmpVal;
    s[count] = tmpVal;
    count ++;
    }
    delete[] s;
}

Answer 2

I am a little confused as to exactly what you're looking for, but I suggest looking into the standard library.

Perhaps something like:

list<string> s;

and then, in the loop use push_back.

Answer 3

I am also confused what is your actual question, because your code works. However, FWIW, I would suggest the following. The changes are: (1) use of const (already suggested by others), (2) use of size_t, (3) change of variable name stringSize to numStrings (because of this I was confused at first glance), and (4) avoiding string copy.

#include <iostream>
#include <string>
using namespace std;

int main()
{
    const size_t numStrings = 7;
    size_t count = 0;

    string s[ numStrings ];

    cout << "\nEnter " << numStrings << " one-word string values:\n";

    while (count < numStrings) {
        cin >> s[ count ];
        count++;
    }

    return 0;
}

Answer 4

Why not read in the entire line, then find all spaces and using the substr method, split the string?

You will need the following methods: getline() find_first_of() substr()

Also, searching around this site for splitting strings in c++ will give you a lot of tips.

Answer 5

First of all, the size of your array should be constant:

const int stringSize = 7;

Secondly, as dbrien said, you should use std::vector unless you're doing this for the learning experience:

std::string tmpVal;
std::vector<std::string> s;
cout << "\nEnter " << stringSize << " one-word string values:\n"; 

while (cin >> tmpVal)
{ 
    s.push_back(tmpVal);
}

Answer 6

First, the array dimension must be constant, so it should be const int stringsize = 7; Also, I would suggest using std::vector rather than std::list, additionally What was the error?

Answer 7

Not sure what error you're getting, but this is wrong because you need to use a constant integral value to allocate arrays on the stack.. Change:

int stringSize = 7;
int count = 0;

string s[stringSize];

... to:

const int stringSize = 7;
int count = 0;

string s[stringSize];

You can and probably should also use a vector instead of using C-style arrays, or trying to hand roll your own templated array class:

vector<string> s;
const int stringSize = 7;

cout << "\nEnter " << stringSize << " one-word string values:\n";

while (s.size()  < stringSize) {

    string tmpVal;

    cin >> tmpVal;
    s.push_back(tmpVal);
}

Answer 8

So it turns out it was the compiler. I was using xCode and getting:

cin_cout(7307) malloc: *** error for object 0x1000072c0: pointer being freed was not allocated

*** set a breakpoint in malloc_error_break to debug

Running the same block in Visual c++ seemed to be ok... Sorry for my stupidity and thanks kindly for all the quick feedback!