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How does strtok work in this case?

  1. Oct 11, 2015 #1
    1. The problem statement, all variables and given/known data
    I have a file which has data set in this way
    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 doesnt detect if the first line has two values or not. If it does, then it should displayed an error.

    2. Relevant equations
    Code (Text):

    int ParseN(char line[])
        char* first;
        char* second;
        int true=1;
        int numberVertices=0;
        char* pt=strtok(line," -");
        char* pt2=strtok(NULL," -");
        if(pt2==NULL) // in this case when I test my file with just one value in the first line, it doesnt detect the NULL
        return 1;

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

    3. The attempt at a solution
    Last edited by a moderator: Oct 11, 2015
  2. jcsd
  3. Oct 11, 2015 #2


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  4. Oct 11, 2015 #3
  5. Oct 11, 2015 #4


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    Maybe because NULL is an invalid pointer (by definition).
  6. Oct 11, 2015 #5
    even the code in the website that you gave me doesnt work
    Code (Text):

    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);


  7. Oct 11, 2015 #6


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    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";).
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