C.Interface.And.Implementations—dynamic arrays的实现

本文链接：https://blog.youkuaiyun.com/ict2014/article/details/18098889

本文深入探讨了动态数组的概念，解释了其作为编程语言中基本数据类型的应用，并详细介绍了数组的创建、初始化、获取元素、修改元素、长度与大小调整、复制等核心操作的实现原理。

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1、An array is a homogeneous sequence of values in which the elements in the sequence are associated one-to-one with indices in a contiguous range.

2、Arrays in some form appear as built-in data types in virtually all programming languages.

动态数组，底层的数据结构很简单，如下图所示：

=========================array.h========================

#ifndef ARRAY_INCLUDED
#define ARRAY_INCLUDED

#define T Array_T
typedef struct T *T;

//exported functions
extern T     Array_new   (int length, int size);
extern void  Array_free  (T *array);
extern int   Array_length(T array);
extern int   Array_size  (T array);
extern void *Array_get   (T array, int i);
extern void *Array_put   (T array, int i, void *elem);
extern void  Array_resize(T array, int length);
extern T     Array_copy  (T array, int length);


#undef T
#endif

========================arrayrep.h===========================

#ifndef ARRAYREP_INCLUDED
#define ARRAYREP_INCLUDED

#define T Array_T

struct T{
    int length;
    int size;
    char *array;
};

extern void ArrayRep_init(T array, int length,
    int size, void *ary);

#undef T
#endif

========================array.c===============================

#include <stdlib.h>
#include <string.h>
#include "assert.h"
#include "array.h"
#include "arrayrep.h"
#include "mem.h"

#define T Array_T

//functions
T Array_new(int length, int size){
    T array;

    NEW(array);
    if(length > 0){
        ArrayRep_init(array, length, size,
            CALLOC(length, size));
    }else{
        ArrayRep_init(array, length, size, NULL);
    }

    return array;
}

void ArrayRep_init(T array, int length, int size,
    void *ary){
    assert(array);
    assert(ary && length > 0 || length == 0 && ary == NULL);
    assert(size > 0);
    array->length = length;
    array->size = size;
    if(length > 0)
        array->array = ary;
    else
        array->array = NULL;
}

void Array_free(T *array){
    assert(array && *array);
    FREE((*array)->array);
    FREE(*array);
}

void *Array_get(T array, int i){
    assert(array);
    assert(i >= 0 && i < array->length);
    return array->array + i*array->size;
}

void *Array_put(T array, int i, void *elem){
    assert(array);
    assert(i >= 0 && i < array->length);
    assert(elem);
    memcpy(array->array + i * array->size, elem, array->size);
    return elem;
}

int Array_length(T array){
    assert(array);
    return array->length;
}

int Array_size(T array){
    assert(array);
    return array->size;
}

void Array_resize(T array, int length){
    assert(array);
    assert(length >= 0);
    if(length == 0){
        FREE(array->array);
    }else if(array->length == 0){
        array->array = ALLOC(length*array->size);
    }else{
        RESIZE(array->array, length*array->size);
    }
    array->length = length;
}

T Array_copy(T array, int length){
    T copy;

    assert(array);
    assert(length >= 0);
    copy = Array_new(length, array->size);
    if(copy->length >= array->length
        && array->length > 0){
        memcpy(copy->array, array->array,
            array->length*array->size);
    }else if(array->length > copy->length
        && copy->length > 0){
        memcpy(copy->array, array->array,
            copy->length*array->size);
    }

    return copy;
}