


A brief discussion of PHP source code 7: About nl2br, ltrim, rtrim, trim functions
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浅谈PHP源码七:关于nl2br, ltrim, rtrim, trim函数
string nl2br ( string string )
Returns string with ‘
‘ inserted before all newlines.
在代码中有注释如下:
/* it is really faster to scan twice and allocate mem once insted scanning once
and constantly reallocing */
程序先计算需要替换的个数,然后一次性计算需要分配的内存大小。从而减少了每次替换都重新分配内存的开销。
由此可见PHP源码的作者的程序优化上下了不少功夫。
源码摘抄如下:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 |
|
ltrim — Strip whitespace (or other characters) from the beginning of a string
rtrim — Strip whitespace (or other characters) from the end of a string
trim — Strip whitespace (or other characters) from the beginning and end of a string
这三个函数都是调用static void php_do_trim(INTERNAL_FUNCTION_PARAMETERS, int mode)
===》PHPAPI char *php_trim(char *c, int len, char *what, int what_len, zval *return_value, int mode TSRMLS_DC)
实现,依据不同的mode(ltrim => 1, rtrim => 2, trim => 3)实现。
对于第二个参数,指过滤的字符,在默认情况下是 空格 \n\r\t\v\0
在程序中可以看到过滤用的字符仅有char mask[256];即ASCII 码的256个值
在使用php_charmask(unsigned char *input, int len, char *mask TSRMLS_DC)函数创建过滤用的字符HASH数组
如果是1或3(程序实现使用的是 mode & 1),则过滤源字符串前面的字符,从头开始遍历每个字符串,直接hash判断是否是需要过滤的字符,直到第一个不是过滤字符的位置结束
如果是2或 3(程序实现使用的是 mode & 2),则过滤源字符串后面的字符,过程与前面类似。
以上就是本文的全部内容,希望对大家的学习有所帮助,更多相关内容请关注PHP中文网!
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浅谈PHP源码六:关于stream_get_wrappers函数
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