Read file into array

This is a discussion on Read file into array within the C Programming forums, part of the General Programming Boards category; I'm trying to read a file into an array. The data (.txt) is in a large table (200X10) and contains ...

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    Read file into array

    I'm trying to read a file into an array. The data (.txt) is in a large table (200X10) and contains both text and integers. I'm just coming back to C after using matlab for a long time, so I'm really just looking for a link to a good refresher on how I can simply import and organize the data using C. Thanks.

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    The "import" of the data would best be done by fgets() to read a line, and then suitable line-parsing. Depending on the format you have two choices:
    1. manually separate out the portions of the string, using for example strtok(). Once you have the component of a string, you would use strcpy() to copy string data and the strtod(), strtol() functions to convert to double and long respectively/
    2. use sscanf() to read the string.

    Which one of the above you use would depend on the exact formatting of the string. If you could post a few "typical" lines of your data it would help.

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    Depends on the format of the file and exactly how much you have to read. If it's line-based entries of numbers and strings, you could create a struct for each entry and a function to read such a line from a FILE *.

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    ZaC
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    I think you could like the example in this reference to fread() function: http://www.cplusplus.com/reference/c...dio/fread.html

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    Quote Originally Posted by ZaC View Post
    I think you could like the example in this reference to fread() function: http://www.cplusplus.com/reference/c...dio/fread.html
    Although fread() tends to be tricky to use with text-input. It would possibly work out OK if every line is the same length. But the benefit over fgets() is small - for large files, the majority of the time consumed would be idle-time waiting for the disk to deliver the file-content. On a small file (and 200 lines is definitely small in this circumstance), I would expect fgets() to read the whole file in less than 0.1 seconds, and you wouldn't be able to see a noticeable improvement on that in using fread(), but with a distinct loss in flexibility.

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    Note when using fgets() that a newline character (\n) will also be stored, so you may want to remove that

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    . . . but if you're using sscanf() or strtol(), you don't have to, because those functions (generally) ignore whitespace.

    Still, here's how you can remove the newline if you so choose:
    Code:
    #include <string.h>
    
    char buffer[BUFSIZ], *p;
    fgets(buffer, sizeof(buffer), stdin);
    if((p = strchr(buffer, '\n'))) *p = 0;
    dwk

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    alright cool, fgets does the trick. now, i used strtok to chop up the array into pieces, but how should i convert from char into float? thanks for your help.

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    Deathray Engineer MacGyver's Avatar
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    If you really meant char * to float, then you could use strtod() to convert it to a double.

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    ok, thanks that seems to work well. one last problem: the file being read begins with a label of non-uniform length before proceeding to the numerical data.

    one string looks like this:
    200004_at 2501.67 2434.94 2424.03 2861.59 2537.48 2656.73

    is there some way i can skip over the label at the beginning so the string only consists of numbers? i'm having some trouble accounting for the labels not being all the same character length.

    thanks.

  11. #11
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    If you can guarantee that there is no whitespace in the label, then that is easily done by reading the label string until you hit upon whitespace. Otherwise, this will be slightly more difficult.

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