strtok

This is a discussion on strtok within the C Programming forums, part of the General Programming Boards category; hi again, i have the following code and it has some problem. after doing strtok for the 1st time, when ...

  1. #1
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    strtok

    hi again, i have the following code and it has some problem. after doing strtok for the 1st time, when i print out the value of line[0], it returns "hello -a" which is correct. then after the next strtok in the for loop, the result by printing line[0] changes to "hello" i did not do anything to change the value.. so how did it got modified? isit because i did temp = strtok(line[i], ""); and line[i] got changed in the process? please help thanks!
    Code:
    char* string;
    string = "hello -a | world -b";
    char** line;
    char** line2;
    char* temp;
    int i, count;
    i = count = 0;
    //do malloc for line and line 2...
    ......
    .....
    
    /*count number of separated commands */
    for(i = 0; i < strlen(string); i++) {
        if(strcmp(string[1], "|") ==0){
            sector ++;
        }
    }
    
    if(sector) {
       temp = strtok(string, "|");
       while(temp) {
          line[i] = temp;
          i++;
          temp = strtok(NULL, "|");
      }
      printf("&#37;s", line[0]"); //returns hello -a
      for(i = 0; i <= count; i++) {
         temp = strtok(line[i], "");
         line2[i] = temp;
      }
      printf("%s", line[0]");  // returns hello
    }
    Last edited by cstudent; 04-23-2008 at 05:19 AM.

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Strtok damages the input string - it replaced the "token" with 0, so you are only seeing part of the string.
    If you don't like the behaviour, you can take a look at my strtok, which is not damaging (the input is always kept intact).
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    thanks i will try it out. however, im still interested in knowing how to overcome this problem. am i right to say that when i do temp = strtok(line[i], " "); , something is modified to line?

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    OK, say you have a string "Hello World". It's an array of chars as thus: 'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '\0'.
    When you print it, it detects the end at the '\0'. But when strtok is run with token " ", the char array will then look like:
    'H', 'e', 'l', 'l', 'o', '\0', 'W', 'o', 'r', 'l', 'd', '\0'.
    (Notice how the space was replaced by '\0'.)
    Therefore, functions think the string ends after "Hello" and stops there.
    That's why strtok is damaging.
    So yes, it modifies the input.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
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    hahahaha i understand now.. kinda crappy :/ now.. i gotta think of another way to overcome this cos i cant use another your awesome strtok function hopefully most of my brain cells will survive.

  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by cstudent View Post
    cos i cant use another your awesome strtok function hopefully most of my brain cells will survive.
    Any specific reason you can't?
    Or do you simply not understand how it works?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  7. #7
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    ah i thought of it. maybe if i create a duplicate of line and use strtok on it instead.... maybe it will work. yea theres a reason. i can only have a set of specific files

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    Yes, it will work. Not the best way, but sure, it will work.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  9. #9
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    heh thanks.

  10. #10
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    oh btw, how do u duplicate a copy of char **line with char** lineDup ??

    do a loop of line and assign values to lineDup??

  11. #11
    C++まいる!Cをこわせ! Elysia's Avatar
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    Depends on what char** is. But basically it's just a pointer to pointer, which probably means it's a dynamically allocated 2D array.
    Most likely (assuming you have a buffer with enough space), just loop through it using strcpy(dest[x], src[x]).
    Last edited by Elysia; 04-23-2008 at 05:49 AM.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  12. #12
    Registered User whiteflags's Avatar
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    >Most likely (assuming you have a buffer with enough space), just loop through it using strcmp(dest[x][y], src[x][y]).
    What?

    Malloc enough space for each line* in the new line**
    Copy over the data from the old line* to the new line*
    And then return the line**

  13. #13
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by citizen View Post
    >Most likely (assuming you have a buffer with enough space), just loop through it using strcmp(dest[x][y], src[x][y]).
    What?
    Oops, my bad. src[x] and dest[x] it should be along with strcpy.
    Ah, this isn't my "C day" it seems
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  14. #14
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    sigh wat a pain the the ass !

  15. #15
    C++まいる!Cをこわせ! Elysia's Avatar
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    Then use my strtok. No such pain in the ass.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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