深入理解PHP之strpos

概述

在php中经常用 strpos 判断字符串是否在另一个字符串中存在, 本文介绍 strpos 函数及其实现。

strpos应用

<?php/* strpos示例 */// testecho 'match:', strpos('xasfsdfbk', 'xasfsdfbk') !== false ? 'true' : 'false', ';', PHP_EOL;echo 'match:', strpos('xasfsdfbk', 'fbk') !== false ? 'true' : 'false', ';', PHP_EOL;echo 'match:', strpos('xasfsdfbk', 'xs') != false ? 'true' : 'false', ';', PHP_EOL;echo 'match:', strpos('xasfsdfbk', 'sfs') !== false ? 'true' : 'false', ';', PHP_EOL;// codestrpos('xasfsdfbk', 'sfs');

Warning: strpos 函数可能返回布尔值 FALSE，但也可能返回等同于 FALSE 的非布尔值。请阅读 布尔类型章节以获取更多信息。应使用 === 运算符来测试此函数的返回值。

strpos系列函数

mb* 相关的函数也可, 比如说mb_strpos是基于字符数执行一个多字节安全的 strpos() 操作。

PHP(strpos)源码

strpos(ext/standard/string.c)

• PHP源码地址

PHP_FUNCTION(strpos){ ???zval *needle; ???zend_string *haystack; ???char *found = NULL; ???char ?needle_char[2]; ???zend_long ?offset = 0;#ifndef FAST_ZPP ???if (zend_parse_parameters(ZEND_NUM_ARGS(), "Sz|l", &haystack, &needle, &offset) == FAILURE) { ???????return; ???}#else ???ZEND_PARSE_PARAMETERS_START(2, 3) ???????Z_PARAM_STR(haystack) ???????Z_PARAM_ZVAL(needle) ???????Z_PARAM_OPTIONAL ???????Z_PARAM_LONG(offset) ???ZEND_PARSE_PARAMETERS_END();#endif ???if (offset < 0) { ???????offset += (zend_long)ZSTR_LEN(haystack); ???} ???if (offset < 0 || (size_t)offset > ZSTR_LEN(haystack)) { ???????php_error_docref(NULL, E_WARNING, "Offset not contained in string"); ???????RETURN_FALSE; ???} ???if (Z_TYPE_P(needle) == IS_STRING) { ???????if (!Z_STRLEN_P(needle)) { ???????????php_error_docref(NULL, E_WARNING, "Empty needle"); ???????????RETURN_FALSE; ???????} ???????found = (char*)php_memnstr(ZSTR_VAL(haystack) + offset, ???????????????????????????Z_STRVAL_P(needle), ???????????????????????????Z_STRLEN_P(needle), ???????????????????????????ZSTR_VAL(haystack) + ZSTR_LEN(haystack)); ???} else { ???????if (php_needle_char(needle, needle_char) != SUCCESS) { ???????????RETURN_FALSE; ???????} ???????needle_char[1] = 0; ???????found = (char*)php_memnstr(ZSTR_VAL(haystack) + offset, ???????????????????????????needle_char, ???????????????????????????1, ???????????????????????????ZSTR_VAL(haystack) + ZSTR_LEN(haystack)); ???} ???if (found) { ???????RETURN_LONG(found - ZSTR_VAL(haystack)); ???} else { ???????RETURN_FALSE; ???}}

php_memnstr(main/php.h)

• PHP源码地址

#define php_memnstr zend_memnstr /* 338 line*/

zend_memnstr(Zend/zend_operators.h)

• PHP源码地址

/* * 此函数的作用是在haystack中查找needle,如果不存在返回null,如果存在，返回指向haystack中needle头字符的指针 */zend_memnstr(const char *haystack, const char *needle, size_t needle_len, const char *end){ ???const char *p = haystack; ???const char ne = needle[needle_len-1]; ???ptrdiff_t off_p; ???size_t off_s; ???if (needle_len == 1) { ???????return (const char *)memchr(p, *needle, (end-p)); ???} ???off_p = end - haystack; ???off_s = (off_p > 0) ? (size_t)off_p : 0; ???if (needle_len > off_s) { ???????return NULL; ???} ???if (EXPECTED(off_s < 1024 || needle_len < 3)) { ???????// 第一个优化，只查找end - needle_len次 ???????end -= needle_len; ???????while (p <= end) { ???????????// 第二个优化，先判断字符串的开头和结尾是否一样再判断整个字符串 ???????????if ((p = (const char *)memchr(p, *needle, (end-p+1))) && ne == p[needle_len-1]) { ???????????????if (!memcmp(needle, p, needle_len-1)) { ???????????????????return p; ???????????????} ???????????} ???????????if (p == NULL) { ???????????????return NULL; ???????????} ???????????p++; ???????} ???????return NULL; ???} else { ???????return zend_memnstr_ex(haystack, needle, needle_len, end); ???}}

memchr(string.h)

• Linux内核版-源码地址

/*头文件：#include <string.h>定义函数：void * memchr(const void *s, char c, size_t n);函数说明：memchr()从头开始搜寻s 所指的内存内容前n 个字节，直到发现第一个值为c 的字节，则返回指向该字节的指针。返回值：如果找到指定的字节则返回该字节的指针，否则返回0。*/#ifndef __HAVE_ARCH_MEMCHRvoid *memchr(const void *s, int c, size_t n){ ???const unsigned char *p = s; ???while (n-- != 0) { ???????????if ((unsigned char)c == *p++) { ???????????return (void *)(p - 1); ???????} ???} ???return NULL;}EXPORT_SYMBOL(memchr);#endif

memcmp(string.h)

• Linux内核版-源码地址

/* 字符串函数memcmp ??原型：extern int memcmp(void *buf1, void *buf2, unsigned int count); ???功能：比较内存区域buf1和buf2的前count个字节 ??说明：当buf1<buf2时，返回值<0 　 ??　 ????当buf1=buf2时，返回值=0 　　 ????????当buf1>buf2时，返回值>0 ???????????????????????????????????????*/#ifndef __HAVE_ARCH_MEMCMP#undef memcmp__visible int memcmp(const void *cs, const void *ct, size_t count){ ???const unsigned char *su1, *su2; ???int res = 0; ???for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--) ???????if ((res = *su1 - *su2) != 0) ???????????break; ???return res;}EXPORT_SYMBOL(memcmp);#endif

提示

strpos函数对大小写敏感。

参考

• php strpos官方文档
• 字符串查找算法

原文地址：https://segmentfault.com/a/1190000015786500

深入理解PHP之strpos

原文地址：https://www.cnblogs.com/lalalagq/p/9979058.html