Problems when using strtok function

Question

Good morning to everybody, :)

I have writen a code in C++ that reads information from a txt file. It takes the information in the first row saving it in a string and then I want to work with this info. I want to read this string and when it finds a "|" character it must jump to a new line. Its something quite easy but I'm having problems when executing and I've been trying to find the problem for hours and I haven't suceed. :( I attached the code.

Thanks in advance for your help.

#include <string>
#include <fstream>
#include <vector>
#include <iostream>

using namespace std;

int main()
{

    ifstream ifs( "C:\\a\\text.txt" );
    string temp;

    getline( ifs, temp ); 
    cout<<temp<<endl;

    string * pch;
    pch = strtok (temp,"|");

    while (pch != NULL)
    {
        printf ("%s\n",pch);
        pch = strtok (NULL, "|");
    }

    system("pause");
    return 0;

}

Answer 1

strtok works with char*, not string*. That's probably why you're experiencing issues.

Since you're implementing this with c++, I suggest you use the string functions instead of strtok:

int main()
{

    ifstream ifs( "C:\\a\\text.txt" );
    string temp;

    getline( ifs, temp ); 
    cout<<temp<<endl;

    size_t tokenPos = temp.find("|");   

    while (tokenPos != string::npos)
    {
        cout << temp.substr(0, tokenPos) << endl;
        temp.erase(0, tokenPos+1);
        tokenPos = temp.find("|");  
    }

    system("pause");
    return 0;

}

To store your text in the values you described in your comment, you'd do the following:

int main() 
{ 
    ifstream ifs( "C:\\a\\text.txt" ); 

    int id; 
    int type; 
    int columns; 
    string temp; 

    getline( ifs, temp ); 
    cout<<temp<<endl; 

    size_t tokenPos = temp.find("|");
    while (tokenPos != string::npos) 
    { 
        int i=0; 
        tokenPos = temp.find("|"); 
        cout << temp.substr(0, tokenPos) << endl; 

        if(i==0)
        { 
            id = atoi(temp.substr(0, tokenPos).c_str()); 
        }
        else if(i==1) 
        { 
            type = atoi(temp.substr(0, tokenPos).c_str()); 
        } 
        else if(i==2) 
        { 
            columns = atoi(temp.substr(0, tokenPos).c_str()); 
        } 

        ++i; 
        temp.erase(0, tokenPos+1); 
    } 

    cout << "ID: " << id << ", Type: " << type << ", Columns: " << columns << endl; 
    system("pause"); 
    return 0; 
}

Answer 2

There are many ways to tokenize a std::string. Here is one way; I chose this primarily because it's simple and self-contained:

int main() {
  using namespace std;
  ifstream ifs("C:/a/text.txt");
  vector<string> bits;  // if you want to save to process
  for (string temp; getline(ifs, temp, '|');) {
    bits.push_back(temp);
    cout << temp << '\n';  // if you want to output each as processed
  }
  return 0;
}

Answer 3

You will find some ways to do that in that question. As you use C++, it is usually not the way to resort to C style functions. Concerning your code, try to give us the exact error. It helps ...

I see lots of problems in your code. Here is a working example from C++ reference :

/* strtok example */
#include <stdio.h>
#include <string.h>

int main ()
{
    char str[] ="- This, a sample string.";
    char * pch;
    printf ("Splitting string \"%s\" into tokens:\n",str);
    pch = strtok (str," ,.-");
    while (pch != NULL)
    {
        printf ("%s\n",pch);
        pch = strtok (NULL, " ,.-");
    }
    return 0;
}

As stated in the doc, you need to give strtok a non-const c-string as it will modify it in order to process tokens.

my2c

Answer 4

Try to change this line

  pch = strtok (temp,"|");

to

  pch = strtok (temp.c_str(),"|");

strtok takes char* (c-style string) not ::std::string (c++ string).

UPDATE2 My mistake. I haven't used strtok for so long. Ok. Try this one:

char* s = new char[temp.size() + 1];
memcpy(s, temp.c_str(), temp.size() + 1);  // copy c-style string with '\0' at the end
const char* pch = strtok(s, "|");
...
delete[] s;