Static array is allocated in undefined area

This is a discussion on Static array is allocated in undefined area within the C Programming forums, part of the General Programming Boards category; Hi all. In the following code the array 'splitbuf' is allocated outside any of the output sections defined by my ...

  1. #1
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    Static array is allocated in undefined area

    Hi all.

    In the following code the array 'splitbuf' is allocated outside any of the output sections defined by my linker command file.

    Code:
    #define QMFB_SPLITBUFSIZE_BATCH (8192/JPC_BATCH_SIZE) .
    
    typedef struct {
    	jpc_fix_t vec[JPC_BATCH_SIZE]; 
    } jpc_batch_t;
    
    static void jpc_qmfb1d_split_batch(jpc_fix_t *startptr, int startind, int endind,
      register int step, jpc_fix_t *lstartptr, int lstartind, int lendind,
      jpc_fix_t *hstartptr, int hstartind, int hendind)
    {
    	jpc_batch_t splitbuf[QMFB_SPLITBUFSIZE_BATCH];
                    .....
                    .....
    I should mean that I have set the stack size sufficiently large, so how come it is not allocated there?

    Regards,
    Esben.

  2. #2
    ATH0 quzah's Avatar
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    How come it's not allocated where? It is a local variable. Provided your array isn't some stupidly huge size, it's allocated on the stack when the function is called. It's destroyed when the function ends. The static keyword as you use it, is only making a static function. Static functions are just like non-static functions, except their scope of visibility is limited to the file they're declared in. It doesn't mean that all of the variables in the function are static.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    >How come it's not allocated where?
    The stack...

    Btw, the array size is rather large, but I have allocated around 20 KB of stack, so I guess it should fit...

  4. #4
    and the hat of wrongness Salem's Avatar
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    > so how come it is not allocated there?
    Because local variables are allocated on the stack at run-time, not link time.

    At best, all the linker knows is that there is a block of memory called .stack or something, and that is where the startup routine will set the initial stack pointer to point to.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  5. #5
    ATH0 quzah's Avatar
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    Quote Originally Posted by esben
    >How come it's not allocated where?
    The stack...
    Quote Originally Posted by quzah
    It is a local variable. [snip]...[/snip] it's allocated on the stack when the function is called. It's destroyed when the function ends.
    See what happens when you actually read?


    Quzah.
    Hope is the first step on the road to disappointment.

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