我的博客
运行以下代码：
$tag = "互联网产品、";$text = rtrim($tag, "、");print_r($text);
我们可能以为会得到的结果是互联网产品，实际结果是互联网产�。为什么会这样呢？
科普
PHP 里使用mb_前缀的都是多字节函数
比如
$str = "abcd";print_r(strlen($str)."\n"); // 4print_r(mb_strlen($str)."\n"); // 4$str = "周梦康";print_r(strlen($str)."\n"); // 9print_r(mb_strlen($str)."\n"); // 3
mb_系列函数是以“多个字节组成的一个字符”为颗粒度来操作的，不带mb_则是按实际的字节数来操作的。
原理
trim 函数文档
string trim ( string $str [, string $character_mask = " \t\n\r\0\x0B" ] )
该函数不是多字节函数，也就是说，汉字这样的多字节字符，会拿其头或尾的单字节来和后面的$character_mask对应的char数组进行匹配，如果在后面的数组中，则删掉，继续匹配。比如：
echo ltrim("bcdf","abc"); // df 如下面的 demo 中的函数string_print_char所示：
、由0xe3 0x80 0x81三字节组成，品由0xe5 0x93 0x81三字节组成。所以在执行rtrim的时候，通过字节比对，会将0x81去掉，导致了最后出现了乱码。 源码探究
查看 PHP7 的源码，然后提炼出下面的小 demo ，方便大家一起学习，其实PHP源码的学习并不难，每天进步一点点。
//// main.c// trim//// Created by 周梦康 on 2017/10/18.// Copyright © 2017年 周梦康. All rights reserved.//#include#include #include void string_print_char(char *str);void php_charmask(unsigned char *input, size_t len, char *mask);char *ltrim(char *str,char *character_mask);char *rtrim(char *str,char *character_mask);int main(int argc, char const *argv[]){ printf("%s\n",ltrim("bcdf","abc")); string_print_char("品"); // e5 93 81 string_print_char("、"); // e3 80 81 printf("%s\n",rtrim("互联网产品、","、")); return 0;}char *ltrim(char *str,char *character_mask){ char *res; char mask[256]; register size_t i; int trimmed = 0; size_t len = strlen(str); php_charmask((unsigned char*)character_mask, strlen(character_mask), mask); for (i = 0; i < len; i++) { if (mask[(unsigned char)str[i]]) { trimmed++; } else { break; } } len -= trimmed; str += trimmed; res = (char *) malloc(sizeof(char) * (len+1)); memcpy(res,str,len); return res;}char *rtrim(char *str,char *character_mask){ char *res; char mask[256]; register size_t i; size_t len = strlen(str); php_charmask((unsigned char*)character_mask, strlen(character_mask), mask); if (len > 0) { i = len - 1; do { if (mask[(unsigned char)str[i]]) { len--; } else { break; } } while (i-- != 0); } res = (char *) malloc(sizeof(char) * (len+1)); memcpy(res,str,len); return res;}void string_print_char(char *str){ unsigned long l = strlen(str); for (int i=0; i < l; i++) { printf("%02hhx\t",str[i]); } printf("\n");}void php_charmask(unsigned char *input, size_t len, char *mask){ unsigned char *end; unsigned char c; memset(mask, 0, 256); for (end = input+len; input < end; input++) { c = *input; mask[c]= 1; }}
如果觉得 demo 还不够清晰的，复制下来，自己执行一次吧~
C 语言基础较差的同学也不用担心，我准备后面专门写一个PHP小白学习 C 语言的系列入门短文哈。解决方案
那么我们就依葫芦画瓢，用 php 本身的多字节函数来实现下吧：
function mb_rtrim($string, $trim, $encoding){ $mask = []; $trimLength = mb_strlen($trim, $encoding); for ($i = 0; $i < $trimLength; $i++) { $item = mb_substr($trim, $i, 1, $encoding); $mask[] = $item; } $len = mb_strlen($string, $encoding); if ($len > 0) { $i = $len - 1; do { $item = mb_substr($string, $i, 1, $encoding); if (in_array($item, $mask)) { $len--; } else { break; } } while ($i-- != 0); } return mb_substr($string, 0, $len, $encoding);}mb_internal_encoding("UTF-8");$tag = "互联网产品、";$encoding = mb_internal_encoding();print_r(mb_rtrim($tag, "、",$encoding)); 当然你也可以使用正则来做。通过上面的函数学习，单字节函数和多字节函数，你学会了吗？
PHP7 相关源码
PHP_FUNCTION(trim){ php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 3);}PHP_FUNCTION(rtrim){ php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 2);}PHP_FUNCTION(ltrim){ php_do_trim(INTERNAL_FUNCTION_PARAM_PASSTHRU, 1);} static void php_do_trim(INTERNAL_FUNCTION_PARAMETERS, int mode){ zend_string *str; zend_string *what = NULL; ZEND_PARSE_PARAMETERS_START(1, 2) Z_PARAM_STR(str) Z_PARAM_OPTIONAL Z_PARAM_STR(what) ZEND_PARSE_PARAMETERS_END(); ZVAL_STR(return_value, php_trim(str, (what ? ZSTR_VAL(what) : NULL), (what ? ZSTR_LEN(what) : 0), mode));} PHPAPI zend_string *php_trim(zend_string *str, char *what, size_t what_len, int mode){ const char *c = ZSTR_VAL(str); size_t len = ZSTR_LEN(str); register size_t i; size_t trimmed = 0; char mask[256]; if (what) { if (what_len == 1) { char p = *what; if (mode & 1) { for (i = 0; i < len; i++) { if (c[i] == p) { trimmed++; } else { break; } } len -= trimmed; c += trimmed; } if (mode & 2) { if (len > 0) { i = len - 1; do { if (c[i] == p) { len--; } else { break; } } while (i-- != 0); } } } else { php_charmask((unsigned char*)what, what_len, mask); if (mode & 1) { for (i = 0; i < len; i++) { if (mask[(unsigned char)c[i]]) { trimmed++; } else { break; } } len -= trimmed; c += trimmed; } if (mode & 2) { if (len > 0) { i = len - 1; do { if (mask[(unsigned char)c[i]]) { len--; } else { break; } } while (i-- != 0); } } } } else { if (mode & 1) { for (i = 0; i < len; i++) { if ((unsigned char)c[i] <= ' ' && (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) { trimmed++; } else { break; } } len -= trimmed; c += trimmed; } if (mode & 2) { if (len > 0) { i = len - 1; do { if ((unsigned char)c[i] <= ' ' && (c[i] == ' ' || c[i] == '\n' || c[i] == '\r' || c[i] == '\t' || c[i] == '\v' || c[i] == '\0')) { len--; } else { break; } } while (i-- != 0); } } } if (ZSTR_LEN(str) == len) { return zend_string_copy(str); } else { return zend_string_init(c, len, 0); }} /* { { { php_charmask * Fills a 256-byte bytemask with input. You can specify a range like 'a..z', * it needs to be incrementing. * Returns: FAILURE/SUCCESS whether the input was correct (i.e. no range errors) */static inline int php_charmask(unsigned char *input, size_t len, char *mask){ unsigned char *end; unsigned char c; int result = SUCCESS; memset(mask, 0, 256); for (end = input+len; input < end; input++) { c=*input; if ((input+3 < end) && input[1] == '.' && input[2] == '.' && input[3] >= c) { memset(mask+c, 1, input[3] - c + 1); input+=3; } else if ((input+1 < end) && input[0] == '.' && input[1] == '.') { /* Error, try to be as helpful as possible: (a range ending/starting with '.' won't be captured here) */ if (end-len >= input) { /* there was no 'left' char */ php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the left of '..'"); result = FAILURE; continue; } if (input+2 >= end) { /* there is no 'right' char */ php_error_docref(NULL, E_WARNING, "Invalid '..'-range, no character to the right of '..'"); result = FAILURE; continue; } if (input[-1] > input[2]) { /* wrong order */ php_error_docref(NULL, E_WARNING, "Invalid '..'-range, '..'-range needs to be incrementing"); result = FAILURE; continue; } /* FIXME: better error (a..b..c is the only left possibility?) */ php_error_docref(NULL, E_WARNING, "Invalid '..'-range"); result = FAILURE; continue; } else { mask[c]=1; } } return result;}/* }}} */