When to free up memory?

This is a discussion on When to free up memory? within the C Programming forums, part of the General Programming Boards category; I've read that when one uses pointers they must free up the memory to make it available to the system ...

  1. #1
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    When to free up memory?

    I've read that when one uses pointers they must free up the memory to make it available to the system again. However, it seems that I run across a lot of source code that uses pointers and does not free up memory aferwards. When exactly am I suppose to free up memory? By what method am I suppose to free up this memory?

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    If u allocate memory dynamically, that is, by using something like malloc ..then you need to free the memory after you are done with using the dynamically allocated space, so that it is available to the system.If you are talking about memory allocated when you declare a certain variable or pointer, you dont have to free it, because the variables(local ones) will be pushed off the stack once the function returns.

    You can use free() to free the memory.
    Last edited by PING; 09-27-2005 at 11:09 AM.
    Code:
    >+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.[-]>++++++++[<++++>-] <.>+++++++++++[<++++++++>-]<-.--------.+++.------.--------.[-]>++++++++[<++++>- ]<+.[-]++++++++++.

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    I don't know what you've read, but you call free() to "free up" memory, when you are done using the pointer. And, depending on the implmentation, a call to free() does not necessarily give the free()'d memory back to the system, especially in the sense that another process can then use that memory.

    You call malloc() or calloc() or maybe realloc() to allocate memory.

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    Does the function need to have the "return 0;" statement in it? Does this apply to both C and C++?

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    Registered User cbastard's Avatar
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    dynamic memory is allocated from heap.you allocate it using malloc...etc.if you allocate memory dynamically you have to deallocate it yourself otherwise there will be a memory leak or system will not get memory.For larger program it may go out of memory.To deallocate use free(argument is pointer to memory) function provided in standard library.free memory when you are done with it.

    >>Does the function need to have the "return 0;" statement in it?
    Only when you are defining a function you need to specify wat it will return,not when you are using it.free is defined in standard library you are just using it like any other function like printf() etc.

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    Frequently Quite Prolix dwks's Avatar
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    Example:
    Code:
    #include <stdio.h>
    
    int main(void) {
        char *s, buf[100];
    
        fgets(buf, sizeof(buf), stdin);
    
        s = malloc(strlen(buf)+1);  /* allocate enough memory for buf + NULL */
        strcpy(s, buf);
    
        /* display the two strings to show that they are the same */
        printf("%s%s", s, buf);
    
        free(s);  /* free the allocated memory */
        return 0;
    }
    dwk

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    Registered User white's Avatar
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    I always wondered... If someone doesn't free any memory ...after quiting the application does the memory "gets" free automaticaly ...or it just stays "taken"
    Last edited by white; 09-27-2005 at 03:27 PM.
    ----------------

  8. #8
    Frequently Quite Prolix dwks's Avatar
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    It depends on the OS. Most systems free allocated memory.
    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


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