PHP的内置函数是如何在内部实现的？

如果你想扩展PHP(编辑/写入)自己的功能,请检查：http://www.php.net/~wez/extending-php.pdf

编辑：

干得好 ：

这是该函数的原始C代码：

/* {{{ proto mixed filter_var(mixed variable [,long filter [,mixed options]])
 * Returns the filtered version of the vriable.
 */
PHP_FUNCTION(filter_var)
{
    long filter = FILTER_DEFAULT;
    zval **filter_args = NULL,*data;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC,"z/|lZ",&data,&filter,&filter_args) == FAILURE) {
        return;
    }

    if (!PHP_FILTER_ID_EXISTS(filter)) {
        RETURN_FALSE;
    }

    MAKE_COPY_ZVAL(&data,return_value);

    php_filter_call(&return_value,filter,filter_args,1,FILTER_REQUIRE_SCALAR TSRMLS_CC);
}
/* }}} */



static void php_filter_call(zval **filtered,long filter,zval **filter_args,const int copy,long filter_flags TSRMLS_DC) /* {{{ */
{
    zval  *options = NULL;
    zval **option;
    char  *charset = NULL;

    if (filter_args && Z_TYPE_PP(filter_args) != IS_ARRAY) {
        long lval;

        PHP_FILTER_GET_LONG_OPT(filter_args,lval);

        if (filter != -1) { /* handler for array apply */
            /* filter_args is the filter_flags */
            filter_flags = lval;

            if (!(filter_flags & FILTER_REQUIRE_ARRAY ||  filter_flags & FILTER_FORCE_ARRAY)) {
                filter_flags |= FILTER_REQUIRE_SCALAR;
            }
        } else {
            filter = lval;
        }
    } else if (filter_args) {
        if (zend_hash_find(HASH_OF(*filter_args),"filter",sizeof("filter"),(void **)&option) == SUCCESS) {
            PHP_FILTER_GET_LONG_OPT(option,filter);
        }

        if (zend_hash_find(HASH_OF(*filter_args),"flags",sizeof("flags"),filter_flags);

            if (!(filter_flags & FILTER_REQUIRE_ARRAY ||  filter_flags & FILTER_FORCE_ARRAY)) {
                filter_flags |= FILTER_REQUIRE_SCALAR;
            }
        }

        if (zend_hash_find(HASH_OF(*filter_args),"options",sizeof("options"),(void **)&option) == SUCCESS) {
            if (filter != FILTER_CALLBACK) {
                if (Z_TYPE_PP(option) == IS_ARRAY) {
                    options = *option;
                }
            } else {
                options = *option;
                filter_flags = 0;
            }
        }
    }

    if (Z_TYPE_PP(filtered) == IS_ARRAY) {
        if (filter_flags & FILTER_REQUIRE_SCALAR) {
            if (copy) {
                SEPARATE_ZVAL(filtered);
            }
            zval_dtor(*filtered);
            if (filter_flags & FILTER_NULL_ON_FAILURE) {
                ZVAL_NULL(*filtered);
            } else {
                ZVAL_FALSE(*filtered);
            }
            return;
        }
        php_zval_filter_recursive(filtered,filter_flags,options,charset,copy TSRMLS_CC);
        return;
    }
    if (filter_flags & FILTER_REQUIRE_ARRAY) {
        if (copy) {
            SEPARATE_ZVAL(filtered);
        }
        zval_dtor(*filtered);
        if (filter_flags & FILTER_NULL_ON_FAILURE) {
            ZVAL_NULL(*filtered);
        } else {
            ZVAL_FALSE(*filtered);
        }
        return;
    }

    php_zval_filter(filtered,copy TSRMLS_CC);
    if (filter_flags & FILTER_FORCE_ARRAY) {
        zval *tmp;

        ALLOC_ZVAL(tmp);
        MAKE_COPY_ZVAL(filtered,tmp);

        zval_dtor(*filtered);

        array_init(*filtered);
        add_next_index_zval(*filtered,tmp);
    }
}

这里是您有效的电子邮件常规：
– 这回答了你的问题.是的,它由内部正则表达式完成.

void php_filter_validate_email(PHP_INPUT_FILTER_PARAM_DECL) /* {{{ */
{
    /*
     * The regex below is based on a regex by Michael Rushton.
     * However,it is not identical.  I changed it to only consider routeable
     * addresses as valid.  Michael's regex considers a@b a valid address
     * which conflicts with section 2.3.5 of RFC 5321 which states that:
     *
     *   Only resolvable,fully-qualified domain names (FQDNs) are permitted
     *   when domain names are used in SMTP.  In other words,names that can
     *   be resolved to MX RRs or address (i.e.,A or AAAA) RRs (as discussed
     *   in Section 5) are permitted,as are CNAME RRs whose targets can be
     *   resolved,in turn,to MX or address RRs.  Local nicknames or
     *   unqualified names MUST NOT be used.
     *
     * This regex does not handle comments and folding whitespace.  While
     * this is technically valid in an email address,these parts aren't
     * actually part of the address itself.
     *
     * Michael's regex carries this copyright:
     *
     * Copyright ? Michael Rushton 2009-10
     * http://squiloople.com/
     * Feel free to use and redistribute this code. But please keep this copyright notice.
     *
     */
    const char regexp[] = "/^(?!(?:(?:x22?x5C[x00-x7E]x22?)|(?:x22?[^x5Cx22]x22?)){255,})(?!(?:(?:x22?x5C[x00-x7E]x22?)|(?:x22?[^x5Cx22]x22?)){65,}@)(?:(?:[x21x23-x27x2Ax2Bx2Dx2F-x39x3Dx3Fx5E-x7E]+)|(?:x22(?:[x01-x08x0Bx0Cx0E-x1Fx21x23-x5Bx5D-x7F]|(?:x5C[x00-x7F]))*x22))(?:.(?:(?:[x21x23-x27x2Ax2Bx2Dx2F-x39x3Dx3Fx5E-x7E]+)|(?:x22(?:[x01-x08x0Bx0Cx0E-x1Fx21x23-x5Bx5D-x7F]|(?:x5C[x00-x7F]))*x22)))*@(?:(?:(?!.*[^.]{64,})(?:(?:(?:xn--)?[a-z0-9]+(?:-[a-z0-9]+)*.){1,126}){1,}(?:(?:[a-z][a-z0-9]*)|(?:(?:xn--)[a-z0-9]+))(?:-[a-z0-9]+)*)|(?:[(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})|(?:(?!(?:.*[a-f0-9][:]]){7,})(?:[a-f0-9]{1,4}){0,5})?::(?:[a-f0-9]{1,5})?)))|(?:(?:IPv6:(?:(?:[a-f0-9]{1,4}){5}:)|(?:(?!(?:.*[a-f0-9]:){5,3})?::(?:[a-f0-9]{1,3}:)?)))?(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))(?:.(?:(?:25[0-5])|(?:2[0-4][0-9])|(?:1[0-9]{2})|(?:[1-9]?[0-9]))){3}))]))$/iD";

    pcre       *re = NULL;
    pcre_extra *pcre_extra = NULL;
    int preg_options = 0;
    int         ovector[150]; /* Needs to be a multiple of 3 */
    int         matches;


    /* The maximum length of an e-mail address is 320 octets,per RFC 2821. */
    if (Z_STRLEN_P(value) > 320) {
        RETURN_VALIDATION_FAILED
    }

    re = pcre_get_compiled_regex((char *)regexp,&pcre_extra,&preg_options TSRMLS_CC);
    if (!re) {
        RETURN_VALIDATION_FAILED
    }
    matches = pcre_exec(re,NULL,Z_STRVAL_P(value),Z_STRLEN_P(value),ovector,3);

    /* 0 means that the vector is too small to hold all the captured substring offsets */
    if (matches < 0) {
        RETURN_VALIDATION_FAILED
    }

}
/* }}} */