Question

I am new to C++, I’m working on tokenizing input. The commented line “cout<< “p: ” << p << endl;” makes the 2nd function call not execute, why?

#include <iostream>
#include <string>
#include <string.h> //for library strtok()
#include <sstream> //for useStringStream()
using namespace std;

void useStrTok(){
    char myString[] = "The quick brown fox";
    char *p = strtok(myString, " ");
    while (p) {
        cout<< "token: " << p<< endl;
        p = strtok(NULL, " ");
        //cout<< "p: " << p << endl;
    }
}    

void useStringStream(){
    string myText("The quick brown fox");
    istringstream iss(myText);
    string token;
    while(getline(iss,token, ' '))
    {
        cout << token << endl;
    }
}

int main(){
    useStrTok();
    useStringStream();
    return 0;
}

Answer 1

Because a null pointer maybe returned by strtok and print null pointer causes the crash. Check validation of pointer before accessing it:

if (p)
{
    cout<< "p: " << p << endl;
}

See strtok reference