String manipulation issues

IDE - CodeBlocks
Compiler - GNU GCC

Hello,

I ran into a C++ exercise has me stumped. A program is to ask for a sentance, then it splits it up into individual words and puts the sentance back together with ampersands inplace of the white space.

My program is able to take the sentance and show it split into words. However, when it goes to show the sentance with the ampersands it errors and ends with "Process terminated with status -1073741819"

I don't understand how I have errored. Any suggestions would be greatly apprecaited.

My code:

Code:

---

#include <iostream>
#include <cstring>

using namespace std;

int main(){
    char *p;
    char string[81];
    char string2[81];

    cout << "Input a string to parse: ";
    cin.getline(string, 81);

    p = strtok(string, ", ");  // gets first token
    strncpy(string2, p, 81);    // copies first token to string2
    strcat(string2, "&");      // concatenate string "&" to string 2
    cout << p << endl;          // print out token

    while(p != NULL){              // Do until end of sentance
        p = strtok(NULL, ", ");    // gets next token
        strncpy(string2, p, 81);    // copies token to string2
        strcat(string2, "&");      // concatenate string "&" to string 2
        cout << p << endl;          // print out token
    }

    cout << string2 << endl;        // print out string2

    return 0;

---

Obviously, "p == NULL". Do this:

Code:

---

if (p)
    cout << p << endl;

---

Don't use strtok, strncpy, strcat or char arrays.
Use std::string and std::cin >> instead.

Thanks for the reply.
The point of this exercise is to use <cstring> functions. The <string> functions have not been covered yet.

This is working code that I am building on. It takes a sentance and prints out the words individually. I am trying to put the words back into a string with ampersands instead of white space.

Code:

---

#include <iostream>
#include <cstring>

using namespace std;

int main()
{
    char *p;
    char string[81];

    cout << "Input a string to parse: ";
    cin.getline(string, 81);

    p = strtok(string, ", ");  // gets first token
    cout << p << endl;          // print out token

    while(p != NULL){              // Do until end of sentance
        p = strtok(NULL, ", ");    // gets next token
        cout << p << endl;          // print out token
    }

    return 0;
}

---

There is a subtle mistake in the while loop. You call strtok and then print out the result, but you do not check if the pointer is null before using cout with the pointer.

Compare your code to the following, which does not result in an exception (note that the degenerate case of a user entering an empty or all-delimiter sentence is also covered):

Code:

---

#include <iostream>
#include <cstring>
 
using namespace std;
 
int main()
{
    char *p;
    char string[81];
 
    cout << "Input a string to parse: ";
    cin.getline(string, 81);
 
    p = strtok(string, ", ");
 
    while (p != nullptr)
    {
        cout << p << endl;
        p = strtok(nullptr, ", ");
       
    }
 
    cout << "Press any key to exit . . ." << endl;
    cin.get();

    return 0;
}

---

You should go through the program step-by-step (mentally or otherwise) to understand what it is doing. You should also use the keyword nullptr instead of NULL.