Storing words from a file to an array

This is a discussion on Storing words from a file to an array within the C Programming forums, part of the General Programming Boards category; Hi I'm trying to store some words from an input file to an array, but I keep getting segmentation faults. ...

  1. #1
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    Storing words from a file to an array

    Hi I'm trying to store some words from an input file to an array, but I keep getting segmentation faults.
    The input text file looks something like this
    135 hello
    124 help
    1 first
    each word is separated by a tab after the number

    The following are some of my codes that are relevant:

    typedef struct mydata Mydata;
    struct mydata {
    int key[5000];
    char *name;
    };

    void inputfile() {
    FILE *input;
    int i, key;
    char name[100];
    Mydata array;

    input = fopen ("testdata.txt", "r");

    for(i=0;i<=MAX && !feof(input); i++)
    {
    fscanf (input, "%d%s", &key, &name);
    array.key[i] = key;
    array.name[i] = strdup (name);
    }

    now say, if I want to do
    printf ("%d%s", array.key[0], array.name[0]);
    I get segmentation fault

    the problem here I think it's I've used strdup wrong, or storing the words in wrong. As it can store numbers with no errors.

    Can someone suggest to me what I'm doing wrong? Have I not assigned spaces for array.name correctly?

    Thanks in advance,
    Will

  2. #2
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    Re: Storing words from a file to an array

    Hi SIKCAR,

    The strdup looks fine. Only the array and indexing the array is not correct:
    Code:
    typedef struct mydata Mydata;
    
    struct mydata {
              int key; /* removed 5000 (I asume MAX = 5000?) */
              char *name;
    };
    
    void inputfile() {
            FILE *input;
            int i, key;
            char name[100];
            Mydata array[MAX];
    
            input = fopen ("testdata.txt", "r");
    
            for(i=0;i<=MAX && !feof(input); i++)
            {
                   fscanf (input, "%d%s", &key, &name);
                   array[i].key = key;
                   array[i].name = strdup (name);
            }
    
    printf ("%d%s", array[0].key, array[0].name);

  3. #3
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    B.t.w. always check return values:
    Code:
    if((input = fopen ("testdata.txt", "r")) == NULL)
    {
       /* fopen failed... */
    }
    
    if(fscanf (input, "%d%s", &key, &name) != 2)
    {
       /* failed to scan 2 items... */
    }

  4. #4
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    >>for(i=0;i<=MAX && !feof(input); i++)
    Don't use feof() in this manner. There are plenty of posts on here telling you why this is wrong.

    And the struct would be better written like this:
    Code:
    typedef struct 
    {
        int key; 
        char *name;
    } Mydata;
    Also, check the return from fopen() to ensure it worked.

    Don't forget to free() all the data you malloc()'d (they're hidden within strdup() ).
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  5. #5
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    Thanks for that, I have also checked for the return values.

    But now I have error compiling the line
    array[i].name = strdup (name);

    "warning: assignment makes pointer from integer without a cast"

    I've tried changing
    char *name; to juse char name;
    in my struct
    but get segmentation fault that way.

  6. #6
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    also, I'm not too familiar at using strdup
    can you please explain how to free the memory malloc()'d by this function?

    Thanks,
    Will

  7. #7
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    >>"warning: assignment makes pointer from integer without a cast"
    What libraries are you #include'ing ? Do you have string.h?

    Freeing the malloc'd data example:
    Code:
    char *name;
    name = strdup(SomeCharArray);
    /* strdup could return NULL, we should really be checking for that. */
    puts(name);
    free(name);
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  8. #8
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    Oh, I forgot to include string.h
    thanks for that

  9. #9
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    Bug

    And just a bug in the program, with the very same code.
    I somehow take in the last element of my input file in twice, and printing them out twice in my for loop.
    ie it prints
    456 aaa
    124 abc
    124 abc
    where there was only one 124 abc in the input file.

    Can anyone see the problem?

  10. #10
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    Re: Bug

    Originally posted by SIKCAR
    And just a bug in the program, with the very same code.
    I somehow take in the last element of my input file in twice, and printing them out twice in my for loop.
    ie it prints
    456 aaa
    124 abc
    124 abc
    where there was only one 124 abc in the input file.

    Can anyone see the problem?
    Yes, and I've already told you why. You're using feof() incorrectly. Check the return from the reading function to determine if you're reached the end of the input.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  11. #11
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    alright thanks

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