分析PHP的similar_text函数

//比较字串,返回两个字串第一个相同字符的区域static void php_similar_str(const char *txt1, int len1, const char *txt2, int len2, int *pos1, int *pos2, int *max){char *p, *q;char *end1 = (char *) txt1 + len1;char *end2 = (char *) txt2 + len2;int l;*max = 0;//遍历字串for (p = (char *) txt1; p < end1; p++) { for (q = (char *) txt2; q < end2; q++) { for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++); if (l > *max) { //保存相同区域信息 *max = l; *pos1 = p - txt1; *pos2 = q - txt2; } }}}

//递归函数,比较txt1和txt2的相同字符数量static int php_similar_char(const char *txt1, int len1, const char *txt2, int len2){int sum;int pos1, pos2, max;

php_similar_str(txt1, len1, txt2, len2, &pos1, &pos2, &max);if ((sum = max)) {//这样写有什么意义?????!!!!!

//递归上次不同部分的前部 if (pos1 && pos2) { sum += php_similar_char(txt1, pos1, txt2, pos2); }

//递归上次不同部分的后部 if ((pos1 + max < len1) && (pos2 + max < len2)) { sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max, txt2 + pos2 + max, len2 - pos2 - max); }}

//返回本次比较后的相同字符数量return sum;}

//PHP函数本身，一堆宏，做了些串转换和返回值换算,主功能由上面两个函数做了。PHP_FUNCTION(similar_text){zval **t1, **t2, **percent;int ac = ZEND_NUM_ARGS();int sim;if (ac < 2 || ac > 3 || zend_get_parameters_ex(ac, &t1, &t2, &percent) == FAILURE) { WRONG_PARAM_COUNT;}

convert_to_string_ex(t1);convert_to_string_ex(t2);

if (ac > 2) { convert_to_double_ex(percent);}if (Z_STRLEN_PP(t1) + Z_STRLEN_PP(t2) == 0) { if (ac > 2) { Z_DVAL_PP(percent) = 0; }

RETURN_LONG(0);}sim = php_similar_char(Z_STRVAL_PP(t1), Z_STRLEN_PP(t1), Z_STRVAL_PP(t2), Z_STRLEN_PP(t2));

if (ac > 2) { Z_DVAL_PP(percent) = sim * 200.0 / (Z_STRLEN_PP(t1) + Z_STRLEN_PP(t2));}

RETURN_LONG(sim);}

所有看出similar_text是根据ASCII做比较的，是不考虑词组问题的。

测试了一下，结果如下：

int main(int argc, char *argv[]){ char *str1='weican wuxin'; char *str2='wuxin weican'; int pos1,pos2,max; php_similar_str(str1,strlen(str1),str2,strlen(str2),&pos1,&pos2,&max); printf('php_similar_str:%d,%d=%dn',pos1,pos2,max); max=php_similar_char(str1,strlen(str1),str2,strlen(str2)); printf('php_similar_char:%dn',max); system('PAUSE'); return 0;}

php_similar_str:0,6=6php_similar_char:6

char *str1='TCP协议通讯工作原a理';char *str2='TCPa协议通讯工作原理';

php_similar_str:3,4=14php_similar_char:19