[PHP source code reading] strpos, strstr and stripos, stristr function, strposstristr_PHP tutorial

[PHP source code reading] strpos, strstr and stripos, stristr function, strposstristr

strpos

<span>mixed</span> <span>strpos</span> ( <span>string</span> <span>$haystack</span>, <span>mixed</span> <span>$needle</span> [, int <span>$offset</span> = 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

<span>$str</span> = "hello"<span>;
</span><span>$pos</span> = <span>strpos</span>(<span>$str</span>, 111<span>);
</span><span>//</span><span> 111的ASCII值是o，因此$pos = 4</span>

strpos core source code

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

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

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:

<span>#define</span> php_memnstr zend_memnstr

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

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

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

    </span><span>//</span><span> 第一个优化，只查找end - needle_len次</span>
    end -=<span> needle_len;

    </span><span>while</span> (p <=<span> end) {
        </span><span>//</span><span> 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</span>
        <span>if</span> ((p = (<span>char</span> *)memchr(p, *needle, (end-p+<span>1</span>))) && ne == p[needle_len-<span>1</span><span>]) {
            </span><span>if</span> (!memcmp(needle, p, needle_len-<span>1</span><span>)) {
                </span><span>return</span><span> p;
            }
        }

        </span><span>if</span> (p ==<span> NULL) {
            </span><span>return</span><span> NULL;
        }

        p</span>++<span>;
    }

    </span><span>return</span><span> NULL;
}</span>

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

never appear in p.

strstr

<span>string</span> <span>strstr</span> ( <span>string</span> <span>$haystack</span>, <span>mixed</span> <span>$needle</span> [, bool <span>$before_needle</span> = <span>false</span> ] )

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

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

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

<span>mixed</span> <span>stripos</span> ( <span>string</span> <span>$haystack</span>, <span>string</span> <span>$needle</span> [, int <span>$offset</span> = 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

<span>string</span> <span>stristr</span> ( <span>string</span> <span>$haystack</span>, <span>mixed</span> <span>$needle</span> [, bool <span>$before_needle</span> = <span>false</span> ] )

Case-insensitive strstr.

Core source code

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

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

        found </span>= php_stristr(haystack_dup, needle_char,    haystack_len, <span>1</span><span>);
    }

    </span><span>if</span><span> (found) {
        found_offset </span>= found -<span> haystack_dup;
        </span><span>if</span><span> (part) {
            RETVAL_STRINGL(haystack, found_offset, </span><span>1</span><span>);
        } </span><span>else</span><span> {
            RETVAL_STRINGL(haystack </span>+ found_offset, haystack_len - found_offset, <span>1</span><span>);
        }
    } </span><span>else</span><span> {
        RETVAL_FALSE;
    }
    
    </span><span>//</span><span> 释放变量</span>
    efree(haystack_dup);

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

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

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 suitable 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.

This is the end of this article. If you still have any questions or suggestions, you can communicate more. It is an original article. The writing style is limited and the talent is shallow. If there is anything wrong in the article, please let me know.

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