217 lines
8.6 KiB
C
217 lines
8.6 KiB
C
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// stretchy_buffer.h - v1.02 - public domain - nothings.org/stb
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// a vector<>-like dynamic array for C
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//
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// version history:
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// 1.02 - compiles as C++, but untested
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// 1.01 - added a "common uses" documentation section
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// 1.0 - fixed bug in the version I posted prematurely
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// 0.9 - rewrite to try to avoid strict-aliasing optimization
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// issues, but won't compile as C++
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//
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// Will probably not work correctly with strict-aliasing optimizations.
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//
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// The idea:
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//
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// This implements an approximation to C++ vector<> for C, in that it
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// provides a generic definition for dynamic arrays which you can
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// still access in a typesafe way using arr[i] or *(arr+i). However,
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// it is simply a convenience wrapper around the common idiom of
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// of keeping a set of variables (in a struct or globals) which store
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// - pointer to array
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// - the length of the "in-use" part of the array
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// - the current size of the allocated array
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//
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// I find it to be single most useful non-built-in-structure when
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// programming in C (hash tables a close second), but to be clear
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// it lacks many of the capabilities of C++ vector<>: there is no
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// range checking, the object address isn't stable (see next section
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// for details), the set of methods available is small (although
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// the file stb.h has another implementation of stretchy buffers
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// called 'stb_arr' which provides more methods, e.g. for insertion
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// and deletion).
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//
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// How to use:
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//
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// Unlike other stb header file libraries, there is no need to
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// define an _IMPLEMENTATION symbol. Every #include creates as
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// much implementation is needed.
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//
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// stretchy_buffer.h does not define any types, so you do not
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// need to #include it to before defining data types that are
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// stretchy buffers, only in files that *manipulate* stretchy
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// buffers.
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//
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// If you want a stretchy buffer aka dynamic array containing
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// objects of TYPE, declare such an array as:
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//
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// TYPE *myarray = NULL;
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//
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// (There is no typesafe way to distinguish between stretchy
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// buffers and regular arrays/pointers; this is necessary to
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// make ordinary array indexing work on these objects.)
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//
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// Unlike C++ vector<>, the stretchy_buffer has the same
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// semantics as an object that you manually malloc and realloc.
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// The pointer may relocate every time you add a new object
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// to it, so you:
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//
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// 1. can't take long-term pointers to elements of the array
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// 2. have to return the pointer from functions which might expand it
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// (either as a return value or by passing it back)
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//
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// Now you can do the following things with this array:
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//
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// sb_free(TYPE *a) free the array
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// sb_count(TYPE *a) the number of elements in the array
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// sb_push(TYPE *a, TYPE v) adds v on the end of the array, a la push_back
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// sb_add(TYPE *a, int n) adds n uninitialized elements at end of array & returns pointer to first added
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// sb_last(TYPE *a) returns an lvalue of the last item in the array
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// a[n] access the nth (counting from 0) element of the array
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//
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// #define STRETCHY_BUFFER_NO_SHORT_NAMES to only export
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// names of the form 'stb_sb_' if you have a name that would
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// otherwise collide.
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//
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// Note that these are all macros and many of them evaluate
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// their arguments more than once, so the arguments should
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// be side-effect-free.
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//
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// Note that 'TYPE *a' in sb_push and sb_add must be lvalues
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// so that the library can overwrite the existing pointer if
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// the object has to be reallocated.
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//
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// In an out-of-memory condition, the code will try to
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// set up a null-pointer or otherwise-invalid-pointer
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// exception to happen later. It's possible optimizing
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// compilers could detect this write-to-null statically
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// and optimize away some of the code, but it should only
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// be along the failure path. Nevertheless, for more security
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// in the face of such compilers, #define STRETCHY_BUFFER_OUT_OF_MEMORY
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// to a statement such as assert(0) or exit(1) or something
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// to force a failure when out-of-memory occurs.
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//
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// Common use:
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//
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// The main application for this is when building a list of
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// things with an unknown quantity, either due to loading from
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// a file or through a process which produces an unpredictable
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// number.
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//
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// My most common idiom is something like:
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//
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// SomeStruct *arr = NULL;
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// while (something)
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// {
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// SomeStruct new_one;
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// new_one.whatever = whatever;
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// new_one.whatup = whatup;
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// new_one.foobar = barfoo;
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// sb_push(arr, new_one);
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// }
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//
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// and various closely-related factorings of that. For example,
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// you might have several functions to create/init new SomeStructs,
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// and if you use the above idiom, you might prefer to make them
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// return structs rather than take non-const-pointers-to-structs,
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// so you can do things like:
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//
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// SomeStruct *arr = NULL;
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// while (something)
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// {
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// if (case_A) {
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// sb_push(arr, some_func1());
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// } else if (case_B) {
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// sb_push(arr, some_func2());
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// } else {
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// sb_push(arr, some_func3());
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// }
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// }
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//
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// Note that the above relies on the fact that sb_push doesn't
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// evaluate its second argument more than once. The macros do
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// evaluate the *array* argument multiple times, and numeric
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// arguments may be evaluated multiple times, but you can rely
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// on the second argument of sb_push being evaluated only once.
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//
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// Of course, you don't have to store bare objects in the array;
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// if you need the objects to have stable pointers, store an array
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// of pointers instead:
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//
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// SomeStruct **arr = NULL;
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// while (something)
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// {
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// SomeStruct *new_one = malloc(sizeof(*new_one));
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// new_one->whatever = whatever;
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// new_one->whatup = whatup;
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// new_one->foobar = barfoo;
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// sb_push(arr, new_one);
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// }
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//
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// How it works:
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//
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// A long-standing tradition in things like malloc implementations
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// is to store extra data before the beginning of the block returned
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// to the user. The stretchy buffer implementation here uses the
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// same trick; the current-count and current-allocation-size are
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// stored before the beginning of the array returned to the user.
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// (This means you can't directly free() the pointer, because the
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// allocated pointer is different from the type-safe pointer provided
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// to the user.)
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//
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// The details are trivial and implementation is straightforward;
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// the main trick is in realizing in the first place that it's
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// possible to do this in a generic, type-safe way in C.
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//
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// LICENSE
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//
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// This software is in the public domain. Where that dedication is not
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// recognized, you are granted a perpetual, irrevocable license to copy,
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// distribute, and modify this file as you see fit.
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#ifndef STB_STRETCHY_BUFFER_H_INCLUDED
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#define STB_STRETCHY_BUFFER_H_INCLUDED
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#ifndef NO_STRETCHY_BUFFER_SHORT_NAMES
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#define sb_free stb_sb_free
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#define sb_push stb_sb_push
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#define sb_count stb_sb_count
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#define sb_add stb_sb_add
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#define sb_last stb_sb_last
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#endif
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#define stb_sb_free(a) ((a) ? free(stb__sbraw(a)),0 : 0)
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#define stb_sb_push(a,v) (stb__sbmaybegrow(a,1), (a)[stb__sbn(a)++] = (v))
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#define stb_sb_count(a) ((a) ? stb__sbn(a) : 0)
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#define stb_sb_add(a,n) (stb__sbmaybegrow(a,n), stb__sbn(a)+=(n), &(a)[stb__sbn(a)-(n)])
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#define stb_sb_last(a) ((a)[stb__sbn(a)-1])
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#define stb__sbraw(a) ((int *) (a) - 2)
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#define stb__sbm(a) stb__sbraw(a)[0]
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#define stb__sbn(a) stb__sbraw(a)[1]
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#define stb__sbneedgrow(a,n) ((a)==0 || stb__sbn(a)+(n) >= stb__sbm(a))
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#define stb__sbmaybegrow(a,n) (stb__sbneedgrow(a,(n)) ? stb__sbgrow(a,n) : 0)
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#define stb__sbgrow(a,n) ((a) = stb__sbgrowf((a), (n), sizeof(*(a))))
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#include <stdlib.h>
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static void * stb__sbgrowf(void *arr, int increment, int itemsize)
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{
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int dbl_cur = arr ? 2*stb__sbm(arr) : 0;
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int min_needed = stb_sb_count(arr) + increment;
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int m = dbl_cur > min_needed ? dbl_cur : min_needed;
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int *p = (int *) realloc(arr ? stb__sbraw(arr) : 0, itemsize * m + sizeof(int)*2);
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if (p) {
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if (!arr)
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p[1] = 0;
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p[0] = m;
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return p+2;
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} else {
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#ifdef STRETCHY_BUFFER_OUT_OF_MEMORY
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STRETCHY_BUFFER_OUT_OF_MEMORY ;
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#endif
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return (void *) (2*sizeof(int)); // try to force a NULL pointer exception later
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}
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}
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#endif // STB_STRETCHY_BUFFER_H_INCLUDED
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