PHP Strpos, Strstr and Stripos, stristr function analysis, strposstristr_php tutorial

Strpos, Strstr and Stripos, stristr function Analysis in PHP, STRPOSSTRISTR

This article for you to analyze the PHP strpos, strstr and Stripos, Stristr function, for your reference, the specific content as follows

Strpos

Mixed Strpos (String $haystack, mixed $needle [, int $offset = 0])
If offset is specified, the lookup starts at the position of offset. Offset cannot be a negative number.

Returns the location of the first occurrence of needle in haystack. Returns False if needle is not found in the haystack.

Needle, if needle is not a string, it is converted to an integer value and assigned the ASCII character of the numeric value. Take a look at the example below.

Example

$str = "Hello"; $pos = Strpos ($STR, 111);//111 ASCII value is O, so $pos = 4strpos core Source if (z_type_p (needle) = = is_string) {   if (! Z_strlen_p (needle)) {     php_error_docref (NULL tsrmls_cc, e_warning, "Empty needle");     Return_false;   }   Call the PHP_MEMNSTR function to find needle   found = php_memnstr (haystack + offset, z_strval_p              (needle), Z_strlen_p              (needle ),              haystack + haystack_len);   } else {     //If it is not a string, it is converted to a number and assigned to the ASCII character of the number.     if (Php_needle_char (needle, Needle_char tsrmls_cc)! = SUCCESS) {        return_false;     }     Set end character     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 is called to convert the needle to an integer number and to its ASCII value.

Find function

The function finally returns the method that the FOUND,PHP_MEMNSTR function implements to find. So go ahead and see what the PHP_MEMNSTR function does:

#define PHP_MEMNSTR Zend_memnstr
PHP_MEMNSTR is a macro definition of function zend_memnstr, see 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;  }  First optimization, find only end-needle_len times  end-= Needle_len;  while (P <= end) {    ///second optimization, first determine whether the beginning and end of the string are the same again to determine the entire string    if (p = (char *) MEMCHR (P, *needle, (end-p+1))) &&am P 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 found in End–needle_len + 1 (that is, haystack_len+1), if P is empty, the first character of Needle is never seen in P.

Strstr

String Strstr (String $haystack, mixed $needle [, bool $before _needle = false])

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

Returns False if the needle does not exist in the haystack.

If Before_needle is true, returns the string needle the first occurrence of the haystack in haystack.

STRSTR Core Source

if (found) {    //calculates the position of found    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, except that the STRSTR function needs to return the haystack part of the string after locating the position. The part variable is the Before_needle variable that is passed when the STRSTR function is called.

Stripos

Mixed Stripos (String $haystack, string $needle [, int $offset = 0])

Case-insensitive Strpos. The implementation is similar to the following, mainly by using a copy and then converting the string you want to compare to lowercase characters before you find it.

Stristr

string Stristr (String $haystack, mixed $needle [, bool $before _needle = false]) is case-insensitive strstr.

Core source

//copy one copy of Haystackhaystack_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));  Call the PHP_STRISTR function to find the value of the Orig_needle.  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;} Release the variable efree (haystack_dup); 

As you can see, found is obtained from PHP_STRISTR and continues to look at 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);  

The function is to turn the string into lowercase and call the PHP_MENNSTR function to find where needle first appeared in haystack.

Summarize

Because Strpos/stripos returns a position, the position is calculated from 0, so it is more appropriate to determine if the lookup failed with = = = False.

Read the source code of PHP is very much, on the one hand you can know the specific implementation of a function of how the principle, on the other hand can learn some programming optimization program.

The above is the whole content of this article, I hope that you learn PHP programming help.

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