Why doesn't this function with strpbrk() work?

Question

Why does my program crash when I try to put delimiter into vector::operators?I'm trying to make a working calculator and I need to find all the operators of the input string in order. All the necessary libraries were included, and the code worked when I was only using 2 numbers and 1 operator. Is the problem that I used the loop incorrectly? I also have a similar function to find the numbers that works and crashes in the same spots.

vector<char>operators;

int main()
{
    string input;
    cin >> input;
    find_operators(input);
}

void find_operators(string X)
{
    char * cX = new char[X.length()];
    strcpy(cX, X.c_str());
    char * delimiter = strpbrk(cX,"+*-/");
    operators.push_back(*delimiter);     //this worked
    while (delimiter != NULL)
    {
        delimiter = strpbrk(delimiter+1, "+-*/");
        cout << "OK";      //makes it to this point then crashes
        operators.push_back(*delimiter);   //this doesn't work
    }
    delete[] cX;
}

Answer 1

You have a couple issues with your code. First:

char * cX = new char[X.length()];
strcpy(cX, X.c_str());

Is incorrect as you are not accounting for the null terminator that you need in cX . length() only returns the number of character in the string and does not count the null terminator. To fix that all you need to do is:

char * cX = new char[X.length() + 1];
strcpy(cX, X.c_str());   //    ^^^^ add one to the size 

The second issue you have is in:

while (delimiter != NULL)
{
    delimiter = strpbrk(delimiter+1, "+-*/");
    cout << "OK";      //makes it to this point then crashes
    operators.push_back(*delimiter);   //this doesn't work
}

You check if delimiter is not null and then you reassign it using strpbrk() . If strpbrk() returns NULL then operators.push_back(*delimiter) is going to fail because you are dereferencing a null pointer. You should be able to change your code to the following to get it to work:

//...
char * delimiter = strpbrk(cX,"+*-/");  // get operator
while (delimiter != NULL) // keep looping while we have an operator
{
    operators.push_back(*delimiter);  // add the operator to the vector
    delimiter = strpbrk(delimiter+1, "+-*/");  // find the next operator     
}
//...