zend php 动态数组

对C语言有过了解的同学,都知道C语内置了数组类型,可是C数组是静态的—数组的长度在编译时期便已确定了长度(分配了内存)。甚至你都不能这么着

对C语言有过了解的同学,都知道C语内置了数组类型,可是C数组是静态的—数组的长度在编译时期便已确定了长度(分配了内存)。甚至你都不能这么着使用

const int arr_size = 100;char foo[arr_size];

使用数组即有较高的随机访问特性,但我们在很多实际运用场景都无法预先知道加载数据的长度,却又不舍得一开始就建立一个“巨大”的固定长度的表(数组)。解决这个问题,可以使用链表(参见链表ADT),或者使用动态数组。这里主要介绍一下后者—-动态数组。其基本思路是先使用库函数mallo()分配一块内存,这块内存块连续存放着相应的数据单元,每个单元占用的内存空间是一样大小,然后,像引用数组那样借用指针引用这块内存,通过指针和偏移量可以随机访问各个单元的数据。当这块内存写满的时候,可以调用库函数realloc()重新分配更大空间的内存(函数realloc()不会丢失原来的内存块上的数据)。

我从php源码目录里zend目录扒了一份动态数据源代码,供大家一起学习。(http://lxr.php.net/xref/PHP_5_2/Zend/zend_dynamic_array.c)

/* file:zend_dynamic_arr.h */#ifndef cstuff_zend_dynamic_arr_h#define cstuff_zend_dynamic_arr_h typedef struct _zend_dynamic_array { char *array; unsigned int element_size; unsigned int current; unsigned int allocated;} dynamic_array; int zend_dynamic_array_init(dynamic_array *darr, unsigned int element_size, unsigned int size);void *zend_dynamic_array_push(dynamic_array *darr);void *zend_dynamic_array_pop(dynamic_array *darr);void *zend_dynamic_array_get(dynamic_array *darr, unsigned int index);int zend_dynamic_array_destroy(dynamic_array *darr);int zend_dynamic_array_length(dynamic_array *darr); #endif /* @file:zend_dynamic_arr.c */#include <stdio.h>#include <stdlib.h>#include "zend_dynamic_arr.h" int zend_dynamic_array_init(dynamic_array *darr, unsigned int element_size, unsigned int size) { darr->array = (char *)malloc(element_size * size); if (darr->array == NULL) { fprintf(stderr, "init(), out of memory/n"); return -1; } darr->element_size = element_size; darr->allocated = size; darr->current = 0; return 0;} void *zend_dynamic_array_push(dynamic_array *darr) { if (darr->current >= darr->allocated) { darr->allocated *= 2; darr->array = (char *)realloc(darr->array, darr->allocated); if (!darr->array) { fprintf(stderr, "push(), out of memory/n"); exit(EXIT_FAILURE); } } return (void *)(darr->array + (darr->current++) * darr->element_size);} void *zend_dynamic_array_get(dynamic_array *darr, unsigned int index) { if (index >= darr->current) { fprintf(stderr, "get(), key error/n"); return NULL; } return (void *)(darr->array + index * darr->element_size);} void *zend_dynamic_array_pop(dynamic_array *darr) { if (darr->current > 0) { return (void *)(darr->array + (--(darr->current)) * darr->element_size); } return NULL;} int zend_dynamic_array_destroy(dynamic_array *darr) { if (!darr->array) { free(darr->array); darr->current = 0; darr->allocated = 0; } return 0;} int zend_dynamic_array_length(dynamic_array *darr) { return darr->current;} char *zend_dynamic_array_ref(dynamic_array *darr) { if (darr->current > 0) { return (char *)darr->array[0]; } return NULL;} /* @file:zend_dynamic_arr_echo.c */#include <stdio.h>#include <stdlib.h>#include "zend_dynamic_arr.h" #define INIT_SIZE 1024 int main(int argc, char **argv) { dynamic_array buffer; char *bp; int c; if (zend_dynamic_array_init(&buffer, sizeof(char), INIT_SIZE) == -1 ) { fprintf(stderr, "init failed/n"); exit(EXIT_FAILURE); } while ((c = getchar()) != EOF) { if ((bp = zend_dynamic_array_push(&buffer)) != NULL) { *bp = (char)c; } } bp = zend_dynamic_array_push(&buffer); if (bp != NULL) { *bp = '/0'; } bp = zend_dynamic_array_get(&buffer, 0); if (bp != NULL) {printf("%s", bp); zend_dynamic_array_destroy(&buffer); } return 0;} /* @file:Makefile_ZDarray */echo_darr:zend_dynamic_arr.o zend_dynamic_arr_echo.c cc -o echo_darr zend_dynamic_arr.o zend_dynamic_arr_echo.czend_dynamic_arr.o:zend_dynamic_arr.hclean: -rm -f echo_zd_array zend_dynamic_arr.o

我们可以另外用一个例程(使用数组)对比,参见代码如下:

#include <stdio.h> #define MAX_SIZE 1024 int main(int argc, char **argv) { char buffer[MAX_SIZE]; int i, c, limit; i = 0, limit = MAX_SIZE; while (--limit > 0 && (c = getchar()) != EOF) { buffer[i++] = (char)c; } if (i > 0) { buffer[i] = '/0';printf("%s", buffer); } return 0;}

最后,我们可以看看两个例程(echo_arr和echo_darr)输出对比,可以看到dynamic array和array的应用场景会不同。

ryoumatoMacBook-Pro:cstuff 3river$ cat linklist.c |./echo_darr |wc -c 3755ryoumatoMacBook-Pro:cstuff 3river$ cat linklist.c |./echo_arr |wc -c 1023ryoumatoMacBook-Pro:cstuff 3river$ cat linklist.c |wc -c 3755
未登录用户
全部评论0
到底啦