Analysis of strpos, strstr and stripos, stristr functions in PHP, strposstristr_PHP tutorial

Analysis of strpos, strstr, stripos, and stristr functions in PHP, strposstristr

This article analyzes strpos, strstr, stripos, and stristr functions in PHP for your reference. Specific content As follows

strpos

mixed strpos ( string $haystack, mixed $needle [, int $offset = 0 ] )
If offset is specified, the search will start from the offset position. offset cannot be negative.

Returns the position where needle first appeared in haystack. Returns FALSE if needle is not found in haystack.

needle, if needle is not a string, it will be converted to an integer value and assigned the ASCII character of the value. Please see the example below.

Example

$str = "hello";
$pos = strpos($str, 111);
// 111的ASCII值是o，因此$pos = 4
strpos核心源码

if (Z_TYPE_P(needle) == IS_STRING) {
   if (!Z_STRLEN_P(needle)) {
     php_error_docref(NULL TSRMLS_CC, E_WARNING, "Empty needle");
     RETURN_FALSE;
   }

   // 调用php_memnstr函数查找needle
   found = php_memnstr(haystack + offset,
              Z_STRVAL_P(needle),
              Z_STRLEN_P(needle),
              haystack + haystack_len);
   } else {
     // 如果不是字符串，转换成数字并赋值为该数字的ASCII字符。
     if (php_needle_char(needle, needle_char TSRMLS_CC) != SUCCESS) {
        RETURN_FALSE;
     }
     //设置结束字符
     needle_char[1] = 0;
     found = php_memnstr(haystack + offset,
              needle_char,
              1,
              haystack + haystack_len);
　　 }
}

One thing to note is that if needle is not a string, the php_needle_char function will be called to convert needle into an integer number and its ASCII value.

Find function

The function finally returns found, and the php_memnstr function implements the search method. Then continue and see what the php_memnstr function does:

#define php_memnstr zend_memnstr
php_memnstr is the macro definition of the function zend_memnstr. View the zend_memnstr function as follows:

static inline char *
zend_memnstr(char *haystack, char *needle, int needle_len, char *end)
{
  char *p = haystack;
  char ne = needle[needle_len-1];
  if (needle_len == 1) {
    return (char *)memchr(p, *needle, (end-p));
  }

  if (needle_len > end-haystack) {
    return NULL;
  }

  // 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 = (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;
}

The first optimization, because (char *)memchr(p, *needle, (end-p 1) is searched in end – needle_len 1 (ie haystack_len 1). If p is empty, it means the first of needle characters

strstr

string strstr ( string $haystack, mixed $needle [, bool $before_needle = false ] )

Returns the string from the first occurrence of needle in haystack to the end.
This function is case-sensitive.

If needle does not exist in haystack, return FALSE.

If before_needle is true, return the string in haystack before the position where needle appears for the first time in haystack.

strstr core source code

if (found) {
    // 计算出found的位置
    found_offset = found - haystack;
    if (part) {
      RETURN_STRINGL(haystack, found_offset, 1);
    } else {
      RETURN_STRINGL(found, haystack_len - found_offset, 1);
    }
}

The first half of the strstr function is similar to strpos. The difference is that after the strstr function finds the position, it needs to return the string in the haystack part. The part variable is the before_needle variable passed when calling the strstr function.

stripos

mixed stripos ( string $haystack, string $needle [, int $offset = 0 ] )

Case-insensitive strpos. The implementation method is similar to the one below, mainly using a copy and converting the strings to be compared into lowercase characters before searching.

stristr

string stristr ( string $haystack, mixed $needle [, bool $before_needle = false ] ) Case-insensitive strstr.

Core source code

// 拷贝一份haystack
haystack_dup = estrndup(haystack, haystack_len);

if (Z_TYPE_P(needle) == IS_STRING) {
  char *orig_needle;
  if (!Z_STRLEN_P(needle)) {
    php_error_docref(NULL TSRMLS_CC, E_WARNING, "Empty needle");
    efree(haystack_dup);
    RETURN_FALSE;
  }
  orig_needle = estrndup(Z_STRVAL_P(needle), Z_STRLEN_P(needle));
  // 调用php_stristr函数找出orig_needle的值。
  found = php_stristr(haystack_dup, orig_needle,  haystack_len, Z_STRLEN_P(needle));
  efree(orig_needle);
} else {
  if (php_needle_char(needle, needle_char TSRMLS_CC) != SUCCESS) {
    efree(haystack_dup);
    RETURN_FALSE;
  }
  needle_char[1] = 0;

  found = php_stristr(haystack_dup, needle_char,  haystack_len, 1);
}

if (found) {
  found_offset = found - haystack_dup;
  if (part) {
    RETVAL_STRINGL(haystack, found_offset, 1);
  } else {
    RETVAL_STRINGL(haystack + found_offset, haystack_len - found_offset, 1);
  }
} else {
  RETVAL_FALSE;
}

// 释放变量
efree(haystack_dup);

You can know that found is obtained from php_stristr. Continue to check the php_stristr function:

PHPAPI char *php_stristr(char *s, char *t, size_t s_len, size_t t_len)
{
  php_strtolower(s, s_len);
  php_strtolower(t, t_len);
  return php_memnstr(s, t, t_len, s + s_len);
} 

The function of this function is to convert the string into lowercase and then call the php_mennstr function to find the position where needle first appears in haystack.

Summary

Because strpos/stripos returns the position, and the position is calculated from 0, it is more appropriate to use === FALSE when judging the search failure.

There is a lot to gain from reading the source code of PHP. On the one hand, you can know the specific implementation principle of a certain function, and on the other hand, you can learn some programming optimization solutions.

The above is the entire content of this article. I hope it will be helpful to everyone in learning PHP programming.