Freeing memory issues

This is a discussion on Freeing memory issues within the C Programming forums, part of the General Programming Boards category; Code: char MakeBig(char c) /*input: letter. output: CAP letter.*/ { if (c >=97 && c<=122) c-=32; return c; } /*------------------------------------------*/ ...

  1. #1
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    Freeing memory issues

    Code:
    char MakeBig(char c) /*input: letter. output: CAP letter.*/
    {
         if (c >=97 && c<=122)
            c-=32;
         return c;
    }
    /*------------------------------------------*/
    char *trim(char *str)
    /*input: a sentence*/
    /*output: the sentence without spaces, and post-space letters capped.*/
    {
    char *str2;
    int str2l=0;
    int Big=1;
    str2=(char *)malloc((strlen(str)+1)*sizeof(char))
    if str2=='\0'
       {
                 printf("Allocation failed!");
                 exit(0);
       }
    for (i=0; i<strlen(str); i++)
       if (str[i]==' ') 
          Big=1;
       else 
            if (Big==1)
               {
                       str2[str2l]=MakeBig(str[i]);
                       Big=0;
                       str2l++;
               }
            else
                {
                       str2[str2l]=str[i];
                       str2l++;
                }
    str2[str2l]='\0';
    /*LINE IN QUESTION FOLLOWS*/
    free(&str2[str2l+1]);
    return str2;
    }
    /*afternote: the idea was of course to release any spare memory.
    Would this be the right way to do it? If not, why? 
    and how to alternatively implement the solution?*/
    Those are 2 functions, the program wasn't written.

    My questions are outlined in the last comment.

    Expecting your reply,

    -Sp00nk.

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    Don't cast malloc(), it's in the FAQ. Include <stdlib.h> and it should work.

  3. #3
    Frequently Quite Prolix dwks's Avatar
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    Code:
    char *p = malloc(sizeof(char)*100);
    if(!p) exit(1);
    /* ... */
    free(p);
    That should work.

    [edit]
    In other words, you don't have to free each char. You can free the whole string in one swoop.
    [/edit]

  4. #4
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    you were not following. I am not to release the whole string. I have to keep the data.

    I was aiming at releasing the spare allocated memory that wasn't used.

    Thanks for the tip on the malloc casting, but my question still stands.

  5. #5
    Frequently Quite Prolix dwks's Avatar
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    realloc()?

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    unfamiliar with it.

    Wouldn't using a pointer be like freeing a complete string from that point on? therefore effectively freeing the spare memory that was allocated and not used?

  7. #7
    Frequently Quite Prolix dwks's Avatar
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    realloc() frees the data, and allocates a new string of the specified size. It chops off all the data on the end if the new size is smaller than the old.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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  8. #8
    Frequently Quite Prolix dwks's Avatar
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    Wouldn't using a pointer be like freeing a complete string from that point on?
    Yes.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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    brilliant. Note taken.
    ---

    However, I still need an answer whether or not the way that I implemented it would work or not. This was in a test, and therefore the question is not directed at "how to fix this program to make it work better" - rather on "should I have points taken off".

    Now, it would seem realloc would be the way to go, but we didn't learn that. Therefore if the implementation above works, I should not be ducked points.

  10. #10
    Frequently Quite Prolix dwks's Avatar
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    I don't know if it will work, but
    Code:
    char MakeBig(char c) /*input: letter. output: CAP letter.*/
    sounds a lot like toupper(), which is in <ctype.h>.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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  11. #11
    Frequently Quite Prolix dwks's Avatar
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    It won't work if you leave out the parantheses in this:
    Code:
    if str2=='\0'
    i is not declared:
    Code:
    for (i=0; i<strlen(str); i++)
    (And I think that < should be a <=).
    dwk

    Seek and ye shall find. quaere et invenies.

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    first comment: you're correct. my mistake in copying the code.

    i is undeclared indeed. The person who checked the test didn't notice either. =)

    no, the < is fine. remember that the index starts from 0; therefore it must run only up until the index which is 1 below the length of the string.

    Ch33rs.

    Still waiting to see if anybody knows if the memory freeing could be done in the way that I did it.

  13. #13
    Frequently Quite Prolix dwks's Avatar
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    What about the toupper() post?
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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  14. #14
    Frequently Quite Prolix dwks's Avatar
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    Code:
    free(&str2[str2l+1]);
    I don't think that will work. str2l+1 isn't an integer, &str2[x] isn't a pointer.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
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    erhm, str2l is an integer. look again.

    and &str2[x] creates a pointer that points to that specific variable. That is good enough when sending to different functions.

    Therefore, in conclusion, this is the equivilent of sending a string pointer "str" without an index. It should effectively free all cells in such a string, since the pointer would point to the first link in the chain, and all the rest of the linked boxes will be freed as well. therefore clearing the memory that is unused.

    ----

    This is my take on things, theoretically, it should work.

    However, I really need an expert opinion on this to confirm.

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