atio-What am I doing wrong?

This is a discussion on atio-What am I doing wrong? within the C Programming forums, part of the General Programming Boards category; Part of my current assignment requires reading input from a file (Using I/O redirection) into a string of char, then ...

  1. #1
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    atio-What am I doing wrong?

    Part of my current assignment requires reading input from a file (Using I/O redirection) into a string of char, then parsing it, converting the numbers to int and saving that to an array of int. However, I can't get atoi to work for it-I'm using a wrong argument for it, but I don't know exactly how to fix it.

    Here's the segment in question:
    Code:
    i = atoi(input[cnt2]);
    I can provide the whole program if you need that as well. What's wrong with my argument?

  2. #2
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    Looks right to me. What is the result, and what is the content of input[cnt2]?

    I prefer to use strtol, as it gives a bit more control over what you do and detection cababilities for errors, but other than that, it shouldn't make any differences.

    --
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  3. #3
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by Acolyte View Post
    Here's the segment in question:
    Code:
    i = atoi(input[cnt2]);
    I can provide the whole program if you need that as well. What's wrong with my argument?
    Might you mean either
    Code:
    i = atoi(input);
    or
    Code:
    i = atoi(&input[cnt2]);
    ?
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  4. #4
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    Changing it to
    Code:
    i = atoi(&input[cnt2]);
    removed the error, but it's still not working. Here's the whole section:

    Code:
    for (cnt2 = 0; cnt2 < 30; cnt2++)
                            {
                                    if (input[cnt2] != ' ')
                                    {
                                            i = atoi(&input[cnt2]);
                                            stack[cnt3] = i;
                                            cnt3++;
                                    }
                            }
    Basically, what it does is counts through (char input[30] and is supposed to, when it finds anything that is not a space (The only inputs will be numbers and spaces), it converts it to int and puts it into (int stack[cnt3].

  5. #5
    Code Goddess Prelude's Avatar
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    >when it finds anything that is not a space
    That strikes me as suspicious. Will all of the numbers only be one digit? If not, are you expecting something like 123 to be broken down into 123, 23, and 3? I'm not sure this is the effect you want:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main ( void )
    {
      const char *p = "123 456 789";
    
      while ( *p != '\0' ) {
        if ( *p != ' ' )
          printf ( "%d\n", atoi ( p ) );
        ++p;
      }
    
      return 0;
    }
    My best code is written with the delete key.

  6. #6
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    Damn-that's something I hadn't considered. How would I go about dealing with multiple-digit numbers, then?

  7. #7
    Code Goddess Prelude's Avatar
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    >How would I go about dealing with multiple-digit numbers, then?
    Use strtol instead. It'll tell you where the conversion stopped, and you can use that to continue. Even better, strtol (and atoi) skip leading whitespace, so it's as simple as this:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main ( void )
    {
      const char *p = "123 456 789";
      char *end = p;
    
      while ( end != NULL && *end != '\0' )
        printf ( "%d\n", strtol ( end, &end, 0 ) );
    
      return 0;
    }
    My best code is written with the delete key.

  8. #8
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    EDIT: NVM, found the problem.
    Last edited by Acolyte; 10-05-2007 at 05:24 PM.

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