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Reading in strings in C

  1. Oct 28, 2005 #1
    I have to read a list of strings in from stdin and store them, stopping when a blank line is entered. Here's what I tried...
    Code (Text):

            const int LINE_CAP = 100;
            const int MAX_LENGTH = 80;

            char *strings[LINE_CAP];
            int strings_index = 0;
            char buffer[MAX_LENGTH];

            printf("%s", "Enter words:\n");
            scanf("%s", buffer);
            while(buffer != "")
                            strings[strings_index] = buffer;
                            scanf("%s", buffer);
    No luck. Does anyone know how to do it?
  2. jcsd
  3. Oct 28, 2005 #2
    is that the proper way to declare an array of strings? if it is then "" may not be the correct termination for a blank.
  4. Oct 28, 2005 #3
    There's quite a few problems with this code.

    First of all, you can't do things like buffer != "" in C. To compare strings you'll need to use the strcmp function. Doing buffer != "" just compares two pointers, which is not at all what you want.

    Second, when you do strings[string_index] = buffer, it does not copy the contents of buffer into strings[string_index]. It merely sets strings[string_index] to point to the same location in memory as buffer. That's certainly not what you want to do. Buffer gets overwritten every pass through the loop.

    Third, there's no guarantee that the lines you read in will fit into buffer. You need to use a formatting option like %79s in scanf to ensure that it doesn't try to read data in past the end of the buffer (and you'll have to make sure that the last character in the string is a NUL, or else functions like strcpy and strcmp and printf will not work). You may want to consider using fgets instead. In fact, since you want to read in lines, you may want to use fgets anyway; scanf will stop when it hits whitespace, not when it hits the end of a line.
  5. Oct 28, 2005 #4
    Ok, I thought I got what you were saying, but I seem to be confused...

    So I tried using while(strcmp(buffer, "")), but that doesn't stop it when I
    enter a blank line.

    And I tried doing *strings[strings_index] = buffer, that didn't work either.

    I'm kind of lost again.
    Last edited: Oct 28, 2005
  6. Oct 28, 2005 #5
    scanf discards whitespace. If you enter a blank line it skips over it and keeps waiting for you to enter data.

    To copy buffer into strings[strings_index] you can use strcpy, as in strcpy(strings[string_index], buffer). But that won't work unless you allocate memory for the string first. strings[string_index] is just a pointer, and since you don't initialize it, it could be pointing anywhere. Either use malloc() to allocate memory for it first, or declare strings using "char strings[LINE_CAP][MAX_LENGTH];" instead.
  7. Oct 29, 2005 #6
    Ok, I got it working! Thanks so much!
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