char arrays, "cutting", resizing etc.

This is a discussion on char arrays, "cutting", resizing etc. within the C Programming forums, part of the General Programming Boards category; I'm doing this (quite simple) operation: - Read a line from a semi-colon-separate file: 00:name:22:name2:blablablablablahblahblah This string has a length ...

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    char arrays, "cutting", resizing etc.

    I'm doing this (quite simple) operation:

    - Read a line from a semi-colon-separate file:

    00:name:22:name2:blablablablablahblahblah

    This string has a length of 104, allowing for the these substring lengths (plus the delimiters):
    2
    16
    2
    16
    64

    However, the size of the strings can be shorter, so the entire string will most often be less than the max length of 104.

    My problem is that I then need to split the elements in this string (based on the delimiters) into new strings (and a couple of ints), which I've defined with the above sizes.

    What I then want to do (which is the actual problem) is:

    1: Cut down the size of the arrays. F.ex. the array which includes the "Name" part of the string has a size of 16 characters. But if the actual contents is only 5 characters, I'd like to get rid of the rest. I know I cannot just resize an array, but is there an "elegant" way of solving this?

    2: More importantly: The string created by fgets(), and hence the last of the new arrays including the last substring (blablablablablahblahblah in this example) includes a line-break character, placed there by fgets(). This i really need to remove. However, I cannot just remove the last two characters of the string, since it might just as well be only 40 characters in the 64-characer long array, and hence a bunch of empty spaces between the last character and the line-break. Is there a good way to loop through a char array looking for a line break, and then removing it?

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    &TH of undefined behavior Fordy's Avatar
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    Registered User ssharish2005's Avatar
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    How about this

    Code:
    if( sscanf( buffer, "%[^:]:%[^:]:%[^:]:%[^:]:%s", part1, part2, part3, part4, part5 ) == 5 )
    {  ... }
    ssharish
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

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    Fordi: Thanks, but C != C++

    ssharinsh: Hmm....exactly what does that do?

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    strtok() is part of the C++ standard library because it was inherited from the C standard library.

    Incidentally, C != C++ will always be false in C and C++ (for all basic types for which the expression compiles).
    Last edited by grumpy; 06-20-2011 at 06:33 AM.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

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    Yah, of course you're right. And I've looked at strtok. The problems remain, however, as strtok just gets the substrings. I can do that manually as well. But:

    1. How to resize a char array of size 16, which only has 5 characters, to size 5.
    2. How to remove a newline character from a char array when you don't know at which index it is?

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    Quote Originally Posted by cnewbie1 View Post
    Yah, of course you're right. And I've looked at strtok. The problems remain, however, as strtok just gets the substrings. I can do that manually as well. But:

    1. How to resize a char array of size 16, which only has 5 characters, to size 5.
    2. How to remove a newline character from a char array when you don't know at which index it is?
    You're missing the point... strtok() splits a string into its sub-parts by inserting nulls at the tokens and returning the start address of the first non-token character after that. In essence it has cut the string down and no part is longer than it needs to be. If you want to copy the strings out of your original buffer --to put them in structs or arrays for example-- you can use malloc() and strcpy() or strdup().

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    I'm running this string through strtok():

    00:name:2:morename:2204a3741a4f4c636acb71cca5da1b0 041446e554d9fb1a2dceec29428491a17

    Code:
    - calling function - reads the above line from a text file and sends it to the split function
    csflsplit_b(line, sizeof(line)/sizeof(char), ":");
    
    void split_b (char line[], int len, char delims[]) {
    	char *result = NULL;						
    	result = strtok(line, delims);
    
    	while (result != NULL) {
    		printf("%s\n", result);
    		result = strtok(NULL, delims);
            }
    }
    Now, this prints out the following:
    Code:
    bob@host ~/stuff $ ./test 
    00
    Neuni
    2
    neuni
    2204a3741a4f4c636acb71cca5da1b0041446e554d9fb1a2dceec29428491a17
    
    bob@host ~/Working-copies/cprojects/nettconf-cli $
    This shows that the last part - 2204a3741a4f4c636acb71cca5da1b0041446e554d9fb1a2dc eec29428491a17 - must have a line-break which strtok includes, doesn't it?

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    You can have more than one delimiter in strtok... in your case you could use ":\n\r\t" to remove tabs and line endings.

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    Ah, of course. Should've read the specification more closely. Frightningly simple. Thanks.

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    Registered User ssharish2005's Avatar
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    Quote Originally Posted by cnewbie1
    This shows that the last part - 2204a3741a4f4c636acb71cca5da1b0041446e554d9fb1a2dc eec29428491a17 - must have a line-break which strtok includes, doesn't it?
    small update to reflect the OP's statment

    Code:
    if( sscanf( buffer, "%[^:]:%[^:]:%[^:]:%[^:]:%[^\n]", part1, part2, part3, part4, part5 ) == 5 )
    { ... }
    ssharish
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

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    Quote Originally Posted by ssharish2005 View Post
    small update to reflect the OP's statment

    Code:
    if( sscanf( buffer, "%[^:]:%[^:]:%[^:]:%[^:]:%[^\n]", part1, part2, part3, part4, part5 ) == 5 )
    { ... }
    ssharish
    Or he could have used ... sscanf(str,"%s:%s:%s:%s:%s"...
    It will do pattern matching with that as well.

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    Building on ssharish2005's code:
    Code:
    if( fscanf( file, "%2[^:]:%16[^:]:%2[^:]:%16[^:]:%64[^\n]", part1, part2, part3, part4, part5 ) == 5 )
    { ... }
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

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    Registered User ssharish2005's Avatar
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    Quote Originally Posted by CommonTater
    Or he could have used ... sscanf(str,"%s:%s:%s:%s:%s"...
    It will do pattern matching with that as well.
    Why do you think this code will work? I say it wont and shall leave it to you to workout why?

    ssharish
    Last edited by ssharish2005; 06-20-2011 at 05:03 PM.
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

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    Quote Originally Posted by ssharish2005 View Post
    Why do you think this could will work? I say it wont and shall leave it to you to workout why?
    ssharish
    Don't be changing the colons to semi-colons like that...
    Editing quoted text is some serious bad juju.

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