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The macro ALLOC_GROW manages several aspects of dynamic memory allocations for arrays: It performs overprovisioning in order to avoid reallocations in future calls, updates the allocation size variable, multiplies the item size and thus allows users to simply specify the item count, performs the reallocation and updates the array pointer. Sometimes this is too much. Add the macro REALLOC_ARRAY, which only takes care of the latter three points and allows users to specfiy the number of items the array can store. It can increase and also decrease the size. Using the macro avoid duplicating the variable name and takes care of the item sizes automatically. Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
40 lines
1.1 KiB
Plaintext
40 lines
1.1 KiB
Plaintext
allocation growing API
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======================
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Dynamically growing an array using realloc() is error prone and boring.
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Define your array with:
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* a pointer (`item`) that points at the array, initialized to `NULL`
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(although please name the variable based on its contents, not on its
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type);
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* an integer variable (`alloc`) that keeps track of how big the current
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allocation is, initialized to `0`;
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* another integer variable (`nr`) to keep track of how many elements the
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array currently has, initialized to `0`.
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Then before adding `n`th element to the item, call `ALLOC_GROW(item, n,
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alloc)`. This ensures that the array can hold at least `n` elements by
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calling `realloc(3)` and adjusting `alloc` variable.
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------------
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sometype *item;
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size_t nr;
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size_t alloc
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for (i = 0; i < nr; i++)
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if (we like item[i] already)
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return;
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/* we did not like any existing one, so add one */
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ALLOC_GROW(item, nr + 1, alloc);
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item[nr++] = value you like;
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------------
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You are responsible for updating the `nr` variable.
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If you need to specify the number of elements to allocate explicitly
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then use the macro `REALLOC_ARRAY(item, alloc)` instead of `ALLOC_GROW`.
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