How does strtok work in this case?

[TheMathNoob]

Homework Statement

I have a file which has data set in this way
1
2 3
4 7
1 2
I have to make a graph with those values considering that the value of the first line corresponds to the vertices and the next two values per line to the edges. I am having troubles with a function that doesn't detect if the first line has two values or not. If it does, then it should displayed an error.

Homework Equations

[/b]

int ParseN(char line[])
{
    char* first;
    char* second;
    int true=1;
    int numberVertices=0;
    char* pt=strtok(line," -");
    printf("%s",pt);
    char* pt2=strtok(NULL," -");
    printf("%s",pt2);
    if(pt2==NULL) // in this case when I test my file with just one value in the first line, it doesn't detect the NULL
    {
        puts("yes");
    }
    else
        puts("no");
    return 1;

}

by the way sorry for not following the directions in the previous post. Now I understand what I have to do

The Attempt at a Solution

 

[Svein]

Use Google - you will get loads of answers. This is one of them: http://www.tutorialspoint.com/c_standard_library/c_function_strtok.htm.

 

[TheMathNoob]

Use Google - you will get loads of answers. This is one of them: http://www.tutorialspoint.com/c_standard_library/c_function_strtok.htm.

My code is not detecting the null

 

[Svein]

My code is not detecting the null

Maybe because NULL is an invalid pointer (by definition).

 

[TheMathNoob]

Maybe because NULL is an invalid pointer (by definition).

even the code in the website that you gave me doesn't work

char str[5]="jk kj";
    char s=" ";
    char* token;
    int counter=0;
    token = strtok(str,s);

      while( token != NULL )
      {
         printf( " %s\n", token );
         token = strtok(NULL,s);
      }    free(str);

 

[Svein]

A slight error: Your first line (char str[5]="jk kj";) has no room for a string terminator. You should use char *str="jk kj"; (or char str[]="jk kj";).